Apache Hadoop Azure support – Hadoop Azure Support: ABFS - Azure Data Lake Storage Gen2

##### General

- Overview
- Single Node Setup
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- FileSystem Shell
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##### Common

- CLI Mini Cluster
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- Secure Mode
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- HTTP Authentication
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##### HDFS

- Architecture
- User Guide
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- NameNode HA With QJM
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- Observer NameNode
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- libhdfs (C API)
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- Provided Storage

##### MapReduce

- Tutorial
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##### MapReduce REST APIs

- MR Application Master
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##### YARN

- Architecture
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##### YARN REST APIs

- Introduction
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##### YARN Service

- Overview
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##### Hadoop Compatible File Systems

- Aliyun OSS
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##### Auth

- Overview
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##### Tools

- Hadoop Streaming
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##### Reference

- Changelog and Release Notes
- Java API docs
- Unix Shell API
- Metrics

##### Configuration

- core-default.xml
- hdfs-default.xml
- hdfs-rbf-default.xml
- mapred-default.xml
- yarn-default.xml
- kms-default.xml
- httpfs-default.xml
- Deprecated Properties

# Hadoop Azure Support: ABFS - Azure Data Lake Storage Gen2

- Introduction
- Features of the ABFS connector.
- Getting started
  - Concepts
- Hierarchical Namespaces (and WASB Compatibility)
- Non-Hierarchical Namespaces
  - Creating an Azure Storage Account
    - Creation through the Azure Portal
  - Creating a new container
  - Listing and examining containers of a Storage Account.
- Configuring ABFS
- Authentication
  - AAD Token fetch retries
  - Default: Shared Key
  - OAuth 2.0 Authentication
    - Client Credentials
    - Username and Password
    - Refresh Token
    - Azure Managed Identity
    - Azure Workload Identity
  - Custom OAuth 2.0 Token Provider
  - Delegation Token Provider
  - Shared Access Signature (SAS) Token Provider
    - Known Issues With SAS
    - Using User Delegation SAS with ABFS
    - Using Account/Service SAS with ABFS
  - User-bound SAS
- Technical notes
  - Proxy setup
  - Security
  - Limitations of the ABFS connector
  - Consistency and Concurrency
  - Performance and Scalability
  - Extensibility
  - Networking Layer:
    - ApacheHttpClient networking layer configuration Options:
    - ApacheHttpClient classpath requirements:
- Other configuration options
  - Client Correlation Options
    - 1. Client CorrelationId Option
    - 1. Correlation IDs Display Options
  - Flush Options
    - 1. Azure Blob File System Flush Options
    - 2. OutputStream Flush Options
  - Hundred Continue Options
  - Account level throttling Options
  - HNS Check Options
  - Access Options
  - Operation Idempotency
  - Primary User Group Options
  - IO Options
  - Security Options
  - Encryption Options
    - Customer-Provided Global Key
    - Encryption Context Provider
  - Server Options
  - Throttling Options
  - Rename Options
  - Infinite Lease Options
  - Perf Options
    - 1. HTTP Request Tracking Options
  - Driver Metric Options
- Troubleshooting
  - ClassNotFoundException: org.apache.hadoop.fs.azurebfs.AzureBlobFileSystem
  - ClassNotFoundException: com.microsoft.azure.storage.StorageErrorCode
  - Server failed to authenticate the request
  - Configuration property _something_.dfs.core.windows.net not found
  - No such file or directory when trying to list a container
  - “HTTP connection to https://login.microsoftonline.com/something failed for getting token from AzureAD. Http response: 200 OK”
  - java.io.IOException: The ownership on the staging directory /tmp/hadoop-yarn/staging/user1/.staging is not as expected. It is owned by <principal_id>. The directory must be owned by the submitter user1 or user1
- Known Issues
- Testing ABFS

## Introduction

The `hadoop-azure` module provides support for the Azure Data Lake Storage Gen2 storage layer through the “abfs” connector

To make it part of Apache Hadoop’s default classpath, make sure that `HADOOP_OPTIONAL_TOOLS` environment variable has `hadoop-azure` in the list, on every machine in the cluster

    export HADOOP_OPTIONAL_TOOLS=hadoop-azure

You can set this locally in your `.profile`/`.bashrc`, but note it won’t propagate to jobs running in-cluster.

See also: * ABFS Driver for FNS (non-HNS) Accounts * Deprecated WASB Driver for FNS (non-HNS) Accounts * Testing of ABFS Driver * WASB Migration Config Support

## Features of the ABFS connector.

- Supports reading and writing data stored in an Azure Blob Storage account.
- Fully Consistent view of the storage across all clients.
- Can read data written through the `deprecated wasb:` connector.
- Presents a hierarchical file system view by implementing the standard Hadoop `FileSystem` interface.
- Supports configuration of multiple Azure Blob Storage accounts.
- Can act as a source or destination of data in Hadoop MapReduce, Apache Hive, Apache Spark.
- Tested at scale on both Linux and Windows by Microsoft themselves.
- Can be used as a replacement for HDFS on Hadoop clusters deployed in Azure infrastructure.

For details on ABFS, consult the following documents:

- A closer look at Azure Data Lake Storage Gen2; MSDN Article from June 28, 2018.
- Storage Tiers

## Getting started

### Concepts

The Azure Storage data model presents 3 core concepts:

- Storage Account: All access is done through a storage account.
- Container: A container is a grouping of multiple blobs. A storage account may have multiple containers. In Hadoop, an entire file system hierarchy is stored in a single container.
- Blob: A file of any type and size. In Hadoop, files are stored in blobs. The internal implementation also uses blobs to persist the file system hierarchy and other metadata.

The ABFS connector connects to classic containers, or those created with Hierarchical Namespaces.

## Hierarchical Namespaces (and WASB Compatibility)

A key aspect of ADLS Gen 2 is its support for hierarchical namespaces These are effectively directories and offer high performance rename and delete operations — something which makes a significant improvement in performance in query engines writing data to, including MapReduce, Spark, Hive, as well as DistCp.

This feature is only available if the container was created with “namespace” support.

You enable namespace support when creating a new Storage Account, by checking the “Hierarchical Namespace” option in the Portal UI, or, when creating through the command line, using the option `--hierarchical-namespace true`

You cannot enable Hierarchical Namespaces on an existing storage account

Containers in a storage account with Hierarchical Namespaces are not (currently) readable through the `deprecated wasb:` connector.

Some of the `az storage` command line commands fail too, for example:

    $ az storage container list --account-name abfswales1

Output:

    Blob API is not yet supported for hierarchical namespace accounts. ErrorCode: BlobApiNotYetSupportedForHierarchicalNamespaceAccounts

## Non-Hierarchical Namespaces

The ABFS driver also has support for non-hierarchical namespace (FNS) accounts to help users migrating from the legacy WASB driver. See FNS-Blob for more details. The service does not recommend using the DFS endpoint for FNS accounts. DFS endpoint over FNS account has now been REMOVED. All requests detected over FNS account are automatically switched to Blob endpoint.

### Creating an Azure Storage Account

The best documentation on getting started with Azure Datalake Gen2 with the abfs connector is Using Azure Data Lake Storage Gen2 with Azure HDInsight clusters

It includes instructions to create it from the Azure command line tool, which can be installed on Windows, MacOS (via Homebrew) and Linux (apt or yum).

The az storage subcommand handles all storage commands, az storage account create does the creation.

Until the ADLS gen2 API support is finalized, you need to add an extension to the ADLS command.

    az extension add --name storage-preview

Check that all is well by verifying that the usage command includes `--hierarchical-namespace`:

    $  az storage account

Output:

    usage: az storage account create [-h] [--verbose] [--debug]
         [--output {json,jsonc,table,tsv,yaml,none}]
         [--query JMESPATH] --resource-group
         RESOURCE_GROUP_NAME --name ACCOUNT_NAME
         [--sku {Standard_LRS,Standard_GRS,Standard_RAGRS,Standard_ZRS,Premium_LRS,Premium_ZRS}]
         [--location LOCATION]
         [--kind {Storage,StorageV2,BlobStorage,FileStorage,BlockBlobStorage}]
         [--tags [TAGS [TAGS ...]]]
         [--custom-domain CUSTOM_DOMAIN]
         [--encryption-services {blob,file,table,queue} [{blob,file,table,queue} ...]]
         [--access-tier {Hot,Cool}]
         [--https-only [{true,false}]]
         [--file-aad [{true,false}]]
         **[--hierarchical-namespace [{true,false}]]**
         [--bypass {None,Logging,Metrics,AzureServices} [{None,Logging,Metrics,AzureServices} ...]]
         [--default-action {Allow,Deny}]
         [--assign-identity]
         [--subscription _SUBSCRIPTION]

You can list locations from `az account list-locations`, which lists the name to refer to in the `--location` argument:

    $ az account list-locations -o table

It would list locations in a table format.

Sample output:

    DisplayName          Latitude    Longitude    Name
    -------------------  ----------  -----------  ------------------
    East Asia            22.267      114.188      eastasia
    Southeast Asia       1.283       103.833      southeastasia
    ....                  ....        ......         .......

Once a location has been chosen, create the account

    az storage account create --verbose \
        --name abfswales1 \
        --resource-group devteam2 \
        --kind StorageV2 \
        --hierarchical-namespace true \
        --location ukwest \
        --sku Standard_LRS \
        --https-only true \
        --encryption-services blob \
        --access-tier Hot \
        --tags owner=engineering \
        --assign-identity \
        --output jsonc

The output of the command is a JSON file, whose `primaryEndpoints` command includes the name of the store endpoint:

    {
      "primaryEndpoints": {
        "blob": "https://abfswales1.blob.core.windows.net/",
        "dfs": "https://abfswales1.dfs.core.windows.net/",
        "file": "https://abfswales1.file.core.windows.net/",
        "queue": "https://abfswales1.queue.core.windows.net/",
        "table": "https://abfswales1.table.core.windows.net/",
        "web": "https://abfswales1.z35.web.core.windows.net/"
      }
    }

The `abfswales1.dfs.core.windows.net` account is the name by which the storage account will be referred to.

Now ask for the connection string to the store, which contains the account key

    az storage account  show-connection-string --name abfswales1
    {
      "connectionString": "DefaultEndpointsProtocol=https;EndpointSuffix=core.windows.net;AccountName=abfswales1;AccountKey=ACCOUNT_KEY_VALUE"
    }

You then need to add the access key to your `core-site.xml`, JCEKs file or use your cluster management tool to set it the option `fs.azure.account.key.STORAGE-ACCOUNT` to this value.

    <property>
      <name>fs.azure.account.key.abfswales1.dfs.core.windows.net</name>
      <value>ACCOUNT_KEY_VALUE</value>
    </property>

#### Creation through the Azure Portal

Creation through the portal is covered in Quickstart: Create an Azure Data Lake Storage Gen2 storage account

Key Steps

1. Create a new Storage Account in a location which suits you.
2. “Basics” Tab: select “StorageV2”.
3. “Advanced” Tab: enable “Hierarchical Namespace”.

You have now created your storage account. Next, get the key for “Shared Key” authentication (default authentication type).

1. Go to the Azure Portal.
2. Select “Storage Accounts”
3. Select the newly created storage account.
4. In the list of settings, locate “Access Keys” and select that.
5. Copy one of the access keys to the clipboard, add to the XML option, set in cluster management tools, Hadoop JCEKS file or KMS store.

### Creating a new container

An Azure storage account can have multiple containers, each with the container name as the userinfo field of the URI used to reference it.

For example, the container “container1” in the storage account just created will have the URL `abfs://container1@abfswales1.dfs.core.windows.net/`

You can create a new container through the ABFS connector, by setting the option `fs.azure.createRemoteFileSystemDuringInitialization` to `true`. Though the same is not supported when AuthType is SAS.

If the container does not exist, an attempt to list it with `hadoop fs -ls` will fail

    $ hadoop fs -ls abfs://container1@abfswales1.dfs.core.windows.net/

    ls: `abfs://container1@abfswales1.dfs.core.windows.net/': No such file or directory

Enable remote FS creation and the second attempt succeeds, creating the container as it does so:

    $ hadoop fs -D fs.azure.createRemoteFileSystemDuringInitialization=true \
     -ls abfs://container1@abfswales1.dfs.core.windows.net/

This is useful for creating accounts on the command line, especially before the `az storage` command supports hierarchical namespaces completely.

### Listing and examining containers of a Storage Account.

You can use the Azure Storage Explorer

## Configuring ABFS

Any configuration can be specified generally (or as the default when accessing all accounts) or can be tied to a specific account. For example, an OAuth identity can be configured for use regardless of which account is accessed with the property `fs.azure.account.oauth2.client.id` or you can configure an identity to be used only for a specific storage account with `fs.azure.account.oauth2.client.id.<account_name>.dfs.core.windows.net`.

This is shown in the Authentication section.

## Authentication

Authentication for ABFS is ultimately granted by Azure Active Directory.

The concepts covered there are beyond the scope of this document to cover; developers are expected to have read and understood the concepts therein to take advantage of the different authentication mechanisms.

What is covered here, briefly, is how to configure the ABFS client to authenticate in different deployment situations.

The ABFS client can be deployed in different ways, with its authentication needs driven by them.

1. With the storage account’s authentication secret in the configuration: “Shared Key”.
2. Using OAuth 2.0 tokens of one form or another.
3. Deployed in-Azure with the Azure VMs providing OAuth 2.0 tokens to the application, “Managed Instance”.
4. Using Shared Access Signature (SAS) tokens provided by a custom implementation of the SASTokenProvider interface.
5. By directly configuring a fixed Shared Access Signature (SAS) token in the account configuration settings files.
6. Using user-bound SAS auth type, which requires both OAuth 2.0 setup (point 2 above) and SAS setup (point 4 above)

Note: While user-bound SAS Authentication is only supported with HNS Enabled accounts, we recommend using HNS Enabled accounts with SAS authentication as well.

What can be changed is what secrets/credentials are used to authenticate the caller.

The authentication mechanism is set in `fs.azure.account.auth.type` (or the account specific variant). The possible values are SharedKey, OAuth, Custom and SAS. For the various OAuth options use the config `fs.azure.account.oauth.provider.type`. Following are the implementations supported ClientCredsTokenProvider, UserPasswordTokenProvider, MsiTokenProvider, RefreshTokenBasedTokenProvider and WorkloadIdentityTokenProvider. An IllegalArgumentException is thrown if the specified provider type is not one of the supported.

All secrets can be stored in JCEKS files. These are encrypted and password protected —use them or a compatible Hadoop Key Management Store wherever possible

### AAD Token fetch retries

The exponential retry policy used for the AAD token fetch retries can be tuned with the following configurations. * `fs.azure.oauth.token.fetch.retry.max.retries`: Sets the maximum number of retries. Default value is 5. * `fs.azure.oauth.token.fetch.retry.min.backoff.interval`: Minimum back-off interval. Added to the retry interval computed from delta backoff. By default this is set as 0. Set the interval in milli seconds. * `fs.azure.oauth.token.fetch.retry.max.backoff.interval`: Maximum back-off interval. Default value is 60000 (sixty seconds). Set the interval in milli seconds. * `fs.azure.oauth.token.fetch.retry.delta.backoff`: Back-off interval between retries. Multiples of this timespan are used for subsequent retry attempts . The default value is 2000 (two seconds). Set the interval in milliseconds.

### Default: Shared Key

This is the simplest authentication mechanism of account + password.

The account name is inferred from the URL; the password, “key”, retrieved from the XML/JCECKs configuration files.

    <property>
      <name>fs.azure.account.auth.type.ACCOUNT_NAME.dfs.core.windows.net</name>
      <value>SharedKey</value>
      <description>
      </description>
    </property>
    <property>
      <name>fs.azure.account.key.ACCOUNT_NAME.dfs.core.windows.net</name>
      <value>ACCOUNT_KEY</value>
      <description>
      The secret password. Never share these.
      </description>
    </property>

Note: The source of the account key can be changed through a custom key provider; one needs to execute a shell script to retrieve it.

A custom key provider class can be provided with the config `fs.azure.account.keyprovider`. If a key provider class is specified the same will be used to get account key. Otherwise the Simple key provider will be used which will use the key specified for the config `fs.azure.account.key`.

To retrieve using shell script, specify the path to the script for the config `fs.azure.shellkeyprovider.script`. ShellDecryptionKeyProvider class use the script specified to retrieve the key.

### OAuth 2.0 Authentication

The below are the main options of identity configurations for OAuth settings. All of these would have OAuth set as the auth type

    <property>
      <name>fs.azure.account.auth.type</name>
      <value>OAuth</value>
      <description>
        Use OAuth authentication
      </description>
    </property>

#### Client Credentials

OAuth 2.0 credentials of (client id, client secret, endpoint) are provided in the configuration/JCEKS file.

The specifics of this process is covered in hadoop-azure-datalake; the key names are slightly different here.

    <property>
      <name>fs.azure.account.auth.type</name>
      <value>OAuth</value>
      <description>
      Use OAuth authentication
      </description>
    </property>
    <property>
      <name>fs.azure.account.oauth.provider.type</name>
      <value>org.apache.hadoop.fs.azurebfs.oauth2.ClientCredsTokenProvider</value>
      <description>
      Use client credentials
      </description>
    </property>
    <property>
      <name>fs.azure.account.oauth2.client.endpoint</name>
      <value>TOKEN_ENDPOINT</value>
      <description>
      URL of OAuth endpoint
      </description>
    </property>
    <property>
      <name>fs.azure.account.oauth2.client.id</name>
      <value>CLIENT_ID</value>
      <description>
      Client ID
      </description>
    </property>
    <property>
      <name>fs.azure.account.oauth2.client.secret</name>
      <value>CLIENT_SECRET</value>
      <description>
      Secret
      </description>
    </property>

#### Username and Password

An OAuth 2.0 endpoint, username and password are provided in the configuration/JCEKS file.

    <property>
      <name>fs.azure.account.auth.type</name>
      <value>OAuth</value>
      <description>
      Use OAuth authentication
      </description>
    </property>
    <property>
      <name>fs.azure.account.oauth.provider.type</name>
      <value>org.apache.hadoop.fs.azurebfs.oauth2.UserPasswordTokenProvider</value>
      <description>
      Use user and password
      </description>
    </property>
    <property>
      <name>fs.azure.account.oauth2.client.endpoint</name>
      <value>TOKEN_ENDPOINT</value>
      <description>
      URL of OAuth 2.0 endpoint
      </description>
    </property>
    <property>
      <name>fs.azure.account.oauth2.user.name</name>
      <value>USERNAME_VALUE</value>
      <description>
      username
      </description>
    </property>
    <property>
      <name>fs.azure.account.oauth2.user.password</name>
      <value>USER_PASSWORD</value>
      <description>
      password for account
      </description>
    </property>

#### Refresh Token

With an existing Oauth 2.0 token, make a request to the Active Directory endpoint `https://login.microsoftonline.com/Common/oauth2/token` for this token to be refreshed.

    <property>
      <name>fs.azure.account.auth.type</name>
      <value>OAuth</value>
      <description>
      Use OAuth 2.0 authentication
      </description>
    </property>
    <property>
      <name>fs.azure.account.oauth.provider.type</name>
      <value>org.apache.hadoop.fs.azurebfs.oauth2.RefreshTokenBasedTokenProvider</value>
      <description>
      Use the Refresh Token Provider
      </description>
    </property>
    <property>
      <name>fs.azure.account.oauth2.refresh.token</name>
      <value>REFRESH_TOKEN</value>
      <description>
      Refresh token
      </description>
    </property>
    <property>
      <name>fs.azure.account.oauth2.refresh.endpoint</name>
      <value>REFRESH_ENDPOINT</value>
      <description>
      Refresh token endpoint
      </description>
    </property>
    <property>
      <name>fs.azure.account.oauth2.client.id</name>
      <value>CLIENT_ID</value>
      <description>
      Optional Client ID
      </description>
    </property>

#### Azure Managed Identity

Azure Managed Identities, formerly “Managed Service Identities”.

OAuth 2.0 tokens are issued by a special endpoint only accessible from the executing VM (`http://169.254.169.254/metadata/identity/oauth2/token`). The issued credentials can be used to authenticate.

The Azure Portal/CLI is used to create the service identity.

    <property>
      <name>fs.azure.account.auth.type</name>
      <value>OAuth</value>
      <description>
      Use OAuth authentication
      </description>
    </property>
    <property>
      <name>fs.azure.account.oauth.provider.type</name>
      <value>org.apache.hadoop.fs.azurebfs.oauth2.MsiTokenProvider</value>
      <description>
      Use MSI for issuing OAuth tokens
      </description>
    </property>
    <property>
      <name>fs.azure.account.oauth2.msi.tenant</name>
      <value>MSI_TENANT_VALUE</value>
      <description>
      Optional MSI Tenant ID
      </description>
    </property>
    <property>
      <name>fs.azure.account.oauth2.msi.endpoint</name>
      <value>TOKEN_ENDPOINT</value>
      <description>
       MSI endpoint
      </description>
    </property>
    <property>
      <name>fs.azure.account.oauth2.client.id</name>
      <value>CLIENT_ID</value>
      <description>
      Optional Client ID
      </description>
    </property>

#### Azure Workload Identity

Azure Workload Identities, formerly “Azure AD pod identity”.

OAuth 2.0 tokens are written to a file that is only accessible from the executing pod (`/var/run/secrets/azure/tokens/azure-identity-token`). The issued credentials can be used to authenticate.

The Azure Portal/CLI is used to create the service identity.

    <property>
      <name>fs.azure.account.auth.type</name>
      <value>OAuth</value>
      <description>
      Use OAuth authentication
      </description>
    </property>
    <property>
      <name>fs.azure.account.oauth.provider.type</name>
      <value>org.apache.hadoop.fs.azurebfs.oauth2.WorkloadIdentityTokenProvider</value>
      <description>
      Use Workload Identity for issuing OAuth tokens
      </description>
    </property>
    <property>
      <name>fs.azure.account.oauth2.msi.tenant</name>
      <value>${env.AZURE_TENANT_ID}</value>
      <description>
      Optional MSI Tenant ID
      </description>
    </property>
    <property>
      <name>fs.azure.account.oauth2.client.id</name>
      <value>${env.AZURE_CLIENT_ID}</value>
      <description>
      Optional Client ID
      </description>
    </property>
    <property>
      <name>fs.azure.account.oauth2.token.file</name>
      <value>${env.AZURE_FEDERATED_TOKEN_FILE}</value>
      <description>
      Token file path
      </description>
    </property>

### Custom OAuth 2.0 Token Provider

A Custom OAuth 2.0 token provider supplies the ABFS connector with an OAuth 2.0 token when its `getAccessToken()` method is invoked.

    <property>
      <name>fs.azure.account.auth.type</name>
      <value>Custom</value>
      <description>
      Custom Authentication
      </description>
    </property>
    <property>
      <name>fs.azure.account.oauth.provider.type</name>
      <value>PROVIDER_TYPE</value>
      <description>
      classname of Custom Authentication Provider
      </description>
    </property>

The declared class must implement `org.apache.hadoop.fs.azurebfs.extensions.CustomTokenProviderAdaptee` and optionally `org.apache.hadoop.fs.azurebfs.extensions.BoundDTExtension`.

The declared class also holds responsibility to implement retry logic while fetching access tokens.

### Delegation Token Provider

A delegation token provider supplies the ABFS connector with delegation tokens, helps renew and cancel the tokens by implementing the CustomDelegationTokenManager interface.

    <property>
      <name>fs.azure.enable.delegation.token</name>
      <value>true</value>
      <description>Make this true to use delegation token provider</description>
    </property>
    <property>
      <name>fs.azure.delegation.token.provider.type</name>
      <value>{fully-qualified-class-name-for-implementation-of-CustomDelegationTokenManager-interface}</value>
    </property>

In case delegation token is enabled, and the config `fs.azure.delegation.token .provider.type` is not provided then an IlleagalArgumentException is thrown.

### Shared Access Signature (SAS) Token Provider

A shared access signature (SAS) provides secure delegated access to resources in your storage account. With a SAS, you have granular control over how a client can access your data. To know more about how SAS Authentication works refer to Grant limited access to Azure Storage resources using shared access signatures (SAS)

There are three types of SAS supported by Azure Storage: - User Delegation SAS: SAS-based authentication works with HNS-enabled ADLS Gen2 accounts (recommended for use with ABFS) and is also supported with non-HNS (FNS) Blob accounts. However, it is NOT SUPPORTED with FNS-DFS accounts. - Service SAS: Global and works at container level. - Account SAS: Global and works at account level.

#### Known Issues With SAS

- SAS Based Authentication works with HNS Enabled ADLS Gen2 Accounts (which is a recommended account type to be used with ABFS). It is also supported with non-HNS (FNS) Blob accounts. It is NOT SUPPORTED with FNS-DFS accounts.
- Certain root level operations are known to fail with SAS Based Authentication.

#### Using User Delegation SAS with ABFS

- Description: ABFS allows you to implement your custom SAS Token Provider that uses your identity to create a user delegation key which then can be used to create SAS instead of storage account key. The declared class must implement `org.apache.hadoop.fs.azurebfs.extensions.SASTokenProvider`.

- Configuration: To use this method with ABFS Driver, specify the following properties in your `core-site.xml` file:

  1. Authentication Type:

         <property>
           <name>fs.azure.account.auth.type</name>
           <value>SAS</value>
         </property>

  2. Custom SAS Token Provider Class:

         <property>
           <name>fs.azure.sas.token.provider.type</name>
           <value>CUSTOM_SAS_TOKEN_PROVIDER_CLASS</value>
         </property>

  Replace `CUSTOM_SAS_TOKEN_PROVIDER_CLASS` with fully qualified class name of your custom token provider implementation. Depending upon the implementation you might need to specify additional configurations that are required by your custom implementation.

- Example: ABFS Hadoop Driver provides a MockDelegationSASTokenProvider implementation that can be used as an example on how to implement your own custom SASTokenProvider. This requires the Application credentials to be specifed using the following configurations apart from above two:

  1. App Service Principle Tenant Id:

         <property>
           <name>fs.azure.test.app.service.principal.tenant.id</name>
           <value>TENANT_ID</value>
         </property>

  2. App Service Principle Object Id:

         <property>
           <name>fs.azure.test.app.service.principal.object.id</name>
           <value>OBJECT_ID</value>
         </property>

  3. App Id:

         <property>
           <name>fs.azure.test.app.id</name>
           <value>APPLICATION_ID</value>
         </property>

  4. App Secret:

         <property>
           <name>fs.azure.test.app.secret</name>
           <value>APPLICATION_SECRET</value>
         </property>

- Security: More secure than Shared Key and allows granting limited access to data without exposing the access key. Recommended to be used only with HNS Enabled, ADLS Gen 2 storage accounts.

#### Using Account/Service SAS with ABFS

- Description: ABFS allows user to use Account/Service SAS for authenticating requests. User can specify them as fixed SAS Token to be used across all the requests.

- Configuration: To use this method with ABFS Driver, specify the following properties in your `core-site.xml` file:

  1. Authentication Type:

         <property>
           <name>fs.azure.account.auth.type</name>
           <value>SAS</value>
         </property>

1. Account SAS (Fixed SAS Token at Account Level): `xml <property> <name>fs.azure.sas.fixed.token.ACCOUNT_NAME</name> <value>FIXED_ACCOUNT_SAS_TOKEN</value> </property>`
   - Replace `FIXED_ACCOUNT_SAS_TOKEN` with fixed Account/Service SAS. You can also generate SAS from Azure portal. Account -> Security + Networking -> Shared Access Signature
   1. Service SAS (Fixed SAS Token at Container Level):

             <property>
               <name>fs.azure.sas.fixed.token.CONTAINER_NAME.ACCOUNT_NAME</name>
               <value>FIXED_SAS_TOKEN</value>
             </property>

   - Replace `FIXED_SERVICE_SAS_TOKEN` with fixed Service SAS. You can also generate SAS from Azure portal. Account -> Data storage -> Containers -> right click on your container and select generate SAS -> Give valid permissions and expiry time -> Click on generate SAS and copy the SAS token.

- Security: Account/Service SAS requires account keys to be used which makes them less secure. There is no scope of having delegated access to different users.

Note: - Preference order for SAS will be: - fs.azure.sas.token.provider.type - fs.azure.sas.fixed.token.CONTAINER_NAME.ACCOUNT_NAME - fs.azure.sas.fixed.token.ACCOUNT_NAME - fs.azure.sas.fixed.token

### User-bound SAS

- Description: The user-bound SAS auth type allows to track the usage of the SAS token generated- something that was not possible in user-delegation SAS authentication type. Reach out to us at ‘askabfs@microsoft.com’ for more information.
- To use this authentication type, both custom SAS token provider class as well as OAuth 2.0 provider type need to be specified.
  - Read the section below for SAS Token Provider class details and example class implementation.
  - There are multiple identity configurations for OAuth Token Provider settings. Listing the main ones below:
    - Client Credentials
    - Custom token provider
    - Managed Identity
    - Workload Identity

  Refer to respective OAuth 2.0 sections above to correctly choose the OAuth provider type - NOTE: User-bound SAS Authentication is only supported with HNS Enabled accounts.

- Configuration: To use this method with ABFS Driver, specify the following properties in your `core-site.xml` file:

  1. Authentication Type:

         <property>
           <name>fs.azure.account.auth.type</name>
           <value>UserboundSASWithOAuth</value>
         </property>

  2. OAuth 2.0 Provider Type:

         <property>
           <name>fs.azure.account.oauth.provider.type</name>
           <value>org.apache.hadoop.fs.azurebfs.oauth2.ADD_CHOSEN_OAUTH_IDENTITY_CONFIGURATION</value>
         </property>

      3. Custom SAS Token Provider Class:
       ```xml
       <property>
         <name>fs.azure.sas.token.provider.type</name>
         <value>CUSTOM_SAS_TOKEN_PROVIDER_CLASS</value>
       </property>
       ```

      - ABFS allows you to implement your custom SAS Token Provider. The declared class must implement
      `org.apache.hadoop.fs.azurebfs.extensions.SASTokenProvider`.
      ABFS Hadoop Driver provides
      a [MockUserBoundSASTokenProvider](https://github.com/apache/hadoop/blob/trunk/hadoop-tools/hadoop-azure/src/test/java/org/apache/hadoop/fs/azurebfs/extensions/MockUserBoundSASTokenProvider.java)
      implementation that can be used as an example on how to implement your own custom
      SASTokenProvider. This requires the Application credentials to be specifed using
      the following configurations apart from above three:
      4. Delegator App Service Principal Tenant Id:
       ```xml
       <property>
         <name>fs.azure.test.app.service.principal.tenant.id</name>
         <value>DELEGATOR_TENANT_ID</value>
       </property>
       ```
      5. Delegator App Service Principal Object Id:
       ```xml
       <property>
         <name>fs.azure.test.app.service.principal.object.id</name>
         <value>DELEGATOR_OBJECT_ID</value>
       </property>
       ```
      6. End-user App Service Principal Tenant Id:
      ```xml
       <property>
         <name>fs.azure.test.end.user.tenant.id</name>
         <value>DELEGATED_TENANT_ID</value>
       </property>
       ```
      7. End-user App Service Principal Object Id:
      ```xml
      <property>
        <name>fs.azure.test.end.user.object.id</name>
        <value>DELEGATED_OBJECT_ID</value>
      </property>

  1. Delegator App Id:

      <property>
      <name>fs.azure.test.app.id</name>
      <value>APPLICATION_ID</value>
      </property>

  1. Delegator App Secret:

      <property>
        <name>fs.azure.test.app.secret</name>
        <value>APPLICATION_SECRET</value>
      </property>

  - Add all additional configs required by the chosen OAuth Token provider from the sections above as well.

## Technical notes

### Proxy setup

The connector uses the JVM proxy settings to control its proxy setup.

See The Oracle Java documentation for the options to set.

As the connector uses HTTPS by default, the `https.proxyHost` and `https.proxyPort` options are those which must be configured.

In MapReduce jobs, including distcp, the proxy options must be set in both the `mapreduce.map.java.opts` and `mapreduce.reduce.java.opts`.

    # this variable is only here to avoid typing the same values twice.
    # It's name is not important.
    export DISTCP_PROXY_OPTS="-Dhttps.proxyHost=web-proxy.example.com -Dhttps.proxyPort=80"

    hadoop distcp \
      -D mapreduce.map.java.opts="$DISTCP_PROXY_OPTS" \
      -D mapreduce.reduce.java.opts="$DISTCP_PROXY_OPTS" \
      -update -skipcrccheck -numListstatusThreads 40 \
      hdfs://namenode:8020/users/alice abfs://backups@account.dfs.core.windows.net/users/alice

Without these settings, even though access to ADLS may work from the command line, `distcp` access can fail with network errors.

### Security

As with other object stores, login secrets are valuable pieces of information. Organizations should have a process for safely sharing them.

### Limitations of the ABFS connector

- File last access time is not tracked.
- Extended attributes are not supported.
- File Checksums are not supported.
- The `Syncable` interfaces `hsync()` and `hflush()` operations are supported if `fs.azure.enable.flush` is set to true (default=true). With the Wasb connector, this limited the number of times either call could be made to 50,000 HADOOP-15478. If abfs has the a similar limit, then excessive use of sync/flush may cause problems.

### Consistency and Concurrency

As with all Azure storage services, the Azure Datalake Gen 2 store offers a fully consistent view of the store, with complete Create, Read, Update, and Delete consistency for data and metadata.

### Performance and Scalability

For containers with hierarchical namespaces, the scalability numbers are, in Big-O-notation, as follows:

Operation | Scalability
--- | ---
File Rename | `O(1)`
File Delete | `O(1)`
Directory Rename: | `O(1)`
Directory Delete | `O(1)`

For non-namespace stores, the scalability becomes:

Operation | Scalability
--- | ---
File Rename | `O(1)`
File Delete | `O(1)`
Directory Rename: | `O(files)`
Directory Delete | `O(files)`

That is: the more files there are, the slower directory operations get.

Further reading: Azure Storage Scalability Targets

### Extensibility

The ABFS connector supports a number of limited-private/unstable extension points for third-parties to integrate their authentication and authorization services into the ABFS client.

- `CustomDelegationTokenManager` : adds ability to issue Hadoop Delegation Tokens.
- `SASTokenProvider`: allows for custom provision of Azure Storage Shared Access Signature (SAS) tokens.
- `CustomTokenProviderAdaptee`: allows for custom provision of Azure OAuth tokens.
- `KeyProvider`.

Consult the source in `org.apache.hadoop.fs.azurebfs.extensions` and all associated tests to see how to make use of these extension points.

Warning These extension points are unstable.

### Networking Layer:

ABFS Driver can use the following networking libraries: - ApacheHttpClient: - Library Documentation. - JDK networking library: - Library documentation. - Default networking library.

The networking library can be configured using the configuration `fs.azure.networking.library` while initializing the filesystem. Following are the supported values: - `JDK_HTTP_URL_CONNECTION` : Use JDK networking library - `APACHE_HTTP_CLIENT` : Use Apache HttpClient [Default]

#### ApacheHttpClient networking layer configuration Options:

Following are the configuration options for ApacheHttpClient networking layer that can be provided at the initialization of the filesystem: 1. `fs.azure.apache.http.client.idle.connection.ttl`: 1. Maximum idle time in milliseconds for a connection to be kept alive in the connection pool. If the connection is not reused within the time limit, the connection shall be closed. 2. Default value: 5000 milliseconds. 2. `fs.azure.apache.http.client.max.cache.connection.size`: 1. Maximum number of connections that can be cached in the connection pool for a filesystem instance. Total number of concurrent connections has no limit. 2. Default value: 5. 3. `fs.azure.apache.http.client.max.io.exception.retries`: 1. Maximum number of times the client will retry on IOExceptions for a single request with ApacheHttpClient networking-layer. Breach of this limit would turn off the future uses of the ApacheHttpClient library in the current JVM instance. 2. Default value: 3.

#### ApacheHttpClient classpath requirements:

ApacheHttpClient is a `compile` maven dependency in hadoop-azure and would be included in the hadoop-azure jar. For using hadoop-azure with ApacheHttpClient no additional information is required in the classpath.

## Other configuration options

Consult the javadocs for `org.apache.hadoop.fs.azurebfs.constants.ConfigurationKeys`, `org.apache.hadoop.fs.azurebfs.constants.FileSystemConfigurations` and `org.apache.hadoop.fs.azurebfs.AbfsConfiguration` for the full list of configuration options and their default values.

### Client Correlation Options

#### 1. Client CorrelationId Option

Config `fs.azure.client.correlationid` provides an option to correlate client requests using this client-provided identifier. This Id will be visible in Azure Storage Analytics logs in the `request-id-header` field. Reference: Storage Analytics log format

This config accepts a string which can be maximum of 72 characters and should contain alphanumeric characters and/or hyphens only. Defaults to empty string if input is invalid.

#### 1. Correlation IDs Display Options

Config `fs.azure.tracingcontext.format` provides an option to select the format of IDs included in the `request-id-header`. This config accepts a String value corresponding to the following enum options. `SINGLE_ID_FORMAT` : clientRequestId `ALL_ID_FORMAT` : all IDs (default) `TWO_ID_FORMAT` : clientCorrelationId:clientRequestId

### Flush Options

#### 1. Azure Blob File System Flush Options

Config `fs.azure.enable.flush` provides an option to render ABFS flush APIs - HFlush() and HSync() to be no-op. By default, this config will be set to true.

Both the APIs will ensure that data is persisted.

#### 2. OutputStream Flush Options

Config `fs.azure.disable.outputstream.flush` provides an option to render OutputStream Flush() API to be a no-op in AbfsOutputStream. By default, this config will be set to true.

Hflush() being the only documented API that can provide persistent data transfer, Flush() also attempting to persist buffered data will lead to performance issues.

### Hundred Continue Options

`fs.azure.account.expect.header.enabled`: This configuration parameter is used to specify whether you wish to send a expect 100 continue header with each append request or not. It is configured to true by default. This flag configures the client to check with the Azure store before uploading a block of data from an output stream. This allows the client to throttle back gracefully -before actually attempting to upload the block. In experiments this provides significant throughput improvements under heavy load. For more information : - https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Expect

### Account level throttling Options

`fs.azure.account.operation.idle.timeout`: This value specifies the time after which the timer for the analyzer (read or write) should be paused until no new request is made again. The default value for the same is 60 seconds.

### HNS Check Options

Config `fs.azure.account.hns.enabled` provides an option to specify whether the storage account is HNS enabled or not. In case the config is not provided, a server call is made to check the same.

### Access Options

Config `fs.azure.enable.check.access` needs to be set true to enable the AzureBlobFileSystem.access().

### Operation Idempotency

Requests failing due to server timeouts and network failures will be retried. PUT/POST operations are idempotent and need no specific handling.

Delete is considered to be idempotent by default if the target does not exist on retry.

### Primary User Group Options

The group name which is part of FileStatus and AclStatus will be set the same as the username if the following config is set to true `fs.azure.skipUserGroupMetadataDuringInitialization`.

### IO Options

The following configs are related to read and write operations.

`fs.azure.io.retry.max.retries`: Sets the number of retries for IO operations. Currently this is used only for the server call retry logic. Used within `AbfsClient` class as part of the ExponentialRetryPolicy. The value should be greater than or equal to 0.

`fs.azure.io.retry.min.backoff.interval`: Sets the minimum backoff interval for retries of IO operations. Currently this is used only for the server call retry logic. Used within `AbfsClient` class as part of the ExponentialRetryPolicy. This value indicates the smallest interval (in milliseconds) to wait before retrying an IO operation. The default value is 500 milliseconds.

`fs.azure.io.retry.max.backoff.interval`: Sets the maximum backoff interval for retries of IO operations. Currently this is used only for the server call retry logic. Used within `AbfsClient` class as part of the ExponentialRetryPolicy. This value indicates the largest interval (in milliseconds) to wait before retrying an IO operation. The default value is 25000 (25 seconds).

`fs.azure.io.retry.backoff.interval`: Sets the default backoff interval for retries of IO operations. Currently this is used only for the server call retry logic. Used within `AbfsClient` class as part of the ExponentialRetryPolicy. This value is used to compute a random delta between 80% and 120% of the specified value. This random delta is then multiplied by an exponent of the current IO retry number (i.e., the default is multiplied by `2^(retryNum - 1)`) and then contstrained within the range of [`fs.azure.io.retry.min.backoff.interval`, `fs.azure.io.retry.max.backoff.interval`] to determine the amount of time to wait before the next IO retry attempt. The default value is 500 milliseconds.

`fs.azure.write.request.size`: To set the write buffer size. Specify the value in bytes. The value should be between 16384 to 104857600 both inclusive (16 KB to 100 MB). The default value will be 8388608 (8 MB).

`fs.azure.read.request.size`: To set the read buffer size.Specify the value in bytes. The value should be between 16384 to 104857600 both inclusive (16 KB to 100 MB). The default value will be 4194304 (4 MB).

`fs.azure.read.alwaysReadBufferSize`: Read request size configured by `fs.azure.read.request.size` will be honoured only when the reads done are in sequential pattern. When the read pattern is detected to be random, read size will be same as the buffer length provided by the calling process. This config when set to true will force random reads to also read in same request sizes as sequential reads. This is a means to have same read patterns as of ADLS Gen1, as it does not differentiate read patterns and always reads by the configured read request size. The default value for this config will be false, where reads for the provided buffer length is done when random read pattern is detected.

`fs.azure.readaheadqueue.depth`: Sets the readahead queue depth in AbfsInputStream. In case the set value is negative the read ahead queue depth will be set as Runtime.getRuntime().availableProcessors(). By default the value will be 2. To disable readaheads, set this value to 0. If your workload is doing only random reads (non-sequential) or you are seeing throttling, you may try setting this value to 0.

`fs.azure.read.readahead.blocksize`: To set the read buffer size for the read aheads. Specify the value in bytes. The value should be between 16384 to 104857600 both inclusive (16 KB to 100 MB). The default value will be 4194304 (4 MB).

`fs.azure.buffered.pread.disable`: By default the positional read API will do a seek and read on input stream. This read will fill the buffer cache in AbfsInputStream and update the cursor positions. If this optimization is true it will skip usage of buffer and do a lock free REST call for reading from blob. This optimization is very much helpful for HBase kind of short random read over a shared AbfsInputStream instance. Note: This is not a config which can be set at cluster level. It can be used as an option on FutureDataInputStreamBuilder. See FileSystem#openFile(Path path)

To run under limited memory situations configure the following. Especially when there are too many writes from the same process.

`fs.azure.write.max.concurrent.requests`: To set the maximum concurrent write requests from an AbfsOutputStream instance to server at any point of time. Effectively this will be the threadpool size within the AbfsOutputStream instance. Set the value in between 1 to 8 both inclusive.

`fs.azure.write.max.requests.to.queue`: To set the maximum write requests that can be queued. Memory consumption of AbfsOutputStream instance can be tuned with this config considering each queued request holds a buffer. Set the value 3 or 4 times the value set for s.azure.write.max.concurrent.requests.

`fs.azure.analysis.period`: The time after which sleep duration is recomputed after analyzing metrics. The default value for the same is 10 seconds.

### Security Options

`fs.azure.always.use.https`: Enforces to use HTTPS instead of HTTP when the flag is made true. Irrespective of the flag, `AbfsClient` will use HTTPS if the secure scheme (ABFSS) is used or OAuth is used for authentication. By default this will be set to true.

`fs.azure.ssl.channel.mode`: Initializing DelegatingSSLSocketFactory with the specified SSL channel mode. Value should be of the enum DelegatingSSLSocketFactory.SSLChannelMode. The default value will be DelegatingSSLSocketFactory.SSLChannelMode.Default.

### Encryption Options

Only one of the following two options can be configured. If config values of both types are set, ABFS driver will throw an exception. If using the global key type, ensure both pre-computed values are provided.

#### Customer-Provided Global Key

A global encryption key can be configured by providing the following pre-computed values. The key will be applied to any new files created post setting the configuration, and will be required in the requests to read ro modify the contents of the files.

`fs.azure.encryption.encoded.client-provided-key`: The Base64 encoded version of the 256-bit encryption key.

`fs.azure.encryption.encoded.client-provided-key-sha`: The Base64 encoded version of the SHA256 has of the 256-bit encryption key.

#### Encryption Context Provider

ABFS driver supports an interface called `EncryptionContextProvider` that can be used as a plugin for clients to provide custom implementations for the encryption framework. This framework allows for an `encryptionContext` and an `encryptionKey` to be generated by the EncryptionContextProvider for a file to be created. The server keeps track of the encryptionContext for each file. To perform subsequent operations such as read on the encrypted file, ABFS driver will fetch the corresponding encryption key from the EncryptionContextProvider implementation by providing the encryptionContext string retrieved from a GetFileStatus request to the server.

`fs.azure.encryption.context.provider.type`: The canonical name of the class implementing EncryptionContextProvider.

### Server Options

`fs.azure.io.read.tolerate.concurrent.append`: When the config is made true, the If-Match header sent to the server for read calls will be set as * otherwise the same will be set with ETag. This is basically a mechanism in place to handle the reads with optimistic concurrency. Please refer the following links for further information. 1. https://docs.microsoft.com/en-us/rest/api/storageservices/datalakestoragegen2/path/read 2. https://azure.microsoft.com/de-de/blog/managing-concurrency-in-microsoft-azure-storage-2/

`fs.azure.list.max.results`: listStatus API fetches the FileStatus information from server in a page by page manner. The config is used to set the maxResults URI param which sets the page size(maximum results per call). The value should be > 0. By default, this will be 5000. Server has a maximum value for this parameter as 5000. So even if the config is above 5000 the response will only contain 5000 entries. Please refer the following link for further information. https://docs.microsoft.com/en-us/rest/api/storageservices/datalakestoragegen2/path/list

`fs.azure.enable.checksum.validation`: When the config is set to true, Content-MD5 headers are sent to the server for read and append calls. This provides a way to verify the integrity of data during transport. This will have performance impact due to MD5 Hash re-computation on Client and Server side. Please refer to the Azure documentation for Read and Append APIs for more details

### Throttling Options

ABFS driver has the capability to throttle read and write operations to achieve maximum throughput by minimizing errors. The errors occur when the account ingress or egress limits are exceeded and, the server-side throttles requests. Server-side throttling causes the retry policy to be used, but the retry policy sleeps for long periods of time causing the total ingress or egress throughput to be as much as 35% lower than optimal. The retry policy is also after the fact, in that it applies after a request fails. On the other hand, the client-side throttling implemented here happens before requests are made and sleeps just enough to minimize errors, allowing optimal ingress and/or egress throughput. By default the throttling mechanism is enabled in the driver. The same can be disabled by setting the config `fs.azure.enable.autothrottling` to false.

### Rename Options

`fs.azure.atomic.rename.key`: Directories for atomic rename support can be specified comma separated in this config. The driver prints the following warning log if the source of the rename belongs to one of the configured directories. “The atomic rename feature is not supported by the ABFS scheme ; however, rename, create and delete operations are atomic if Namespace is enabled for your Azure Storage account.” The directories can be specified as comma separated values. By default the value is “/hbase”

### Infinite Lease Options

`fs.azure.infinite-lease.directories`: Directories for infinite lease support can be specified comma separated in this config. By default, multiple clients will be able to write to the same file simultaneously. When writing to files contained within the directories specified in this config, the client will obtain a lease on the file that will prevent any other clients from writing to the file. When the output stream is closed, the lease will be released. To revoke a client’s write access for a file, the AzureBlobFilesystem breakLease method may be called. If the client dies before the file can be closed and the lease released, breakLease will need to be called before another client will be able to write to the file.

`fs.azure.lease.threads`: This is the size of the thread pool that will be used for lease operations for infinite lease directories. By default the value is 0, so it must be set to at least 1 to support infinite lease directories.

### Perf Options

#### 1. HTTP Request Tracking Options

If you set `fs.azure.abfs.latency.track` to `true`, the module starts tracking the performance metrics of ABFS HTTP traffic. To obtain these numbers on your machine or cluster, you will also need to enable debug logging for the `AbfsPerfTracker` class in your `log4j` config. A typical perf log line appears like:

    h=KARMA t=2019-10-25T20:21:14.518Z a=abfstest01.dfs.core.windows.net
    c=abfs-testcontainer-84828169-6488-4a62-a875-1e674275a29f cr=delete ce=deletePath
    r=Succeeded l=32 ls=32 lc=1 s=200 e= ci=95121dae-70a8-4187-b067-614091034558
    ri=97effdcf-201f-0097-2d71-8bae00000000 ct=0 st=0 rt=0 bs=0 br=0 m=DELETE
    u=https%3A%2F%2Fabfstest01.dfs.core.windows.net%2Ftestcontainer%2Ftest%3Ftimeout%3D90%26recursive%3Dtrue

The fields have the following definitions:

`h`: host name `t`: time when this request was logged `a`: Azure storage account name `c`: container name `cr`: name of the caller method `ce`: name of the callee method `r`: result (Succeeded/Failed) `l`: latency (time spent in callee) `ls`: latency sum (aggregate time spent in caller; logged when there are multiple callees; logged with the last callee) `lc`: latency count (number of callees; logged when there are multiple callees; logged with the last callee) `s`: HTTP Status code `e`: Error code `ci`: client request ID `ri`: server request ID `ct`: connection time in milliseconds `st`: sending time in milliseconds `rt`: receiving time in milliseconds `bs`: bytes sent `br`: bytes received `m`: HTTP method (GET, PUT etc) `u`: Encoded HTTP URL

Note that these performance numbers are also sent back to the ADLS Gen 2 API endpoints in the `x-ms-abfs-client-latency` HTTP headers in subsequent requests. Azure uses these settings to track their end-to-end latency.

### Driver Metric Options

Config `fs.azure.metric.format` provides an option to select the format of IDs included in the `header` for metrics. This config accepts a String value corresponding to the following enum options. `INTERNAL_METRIC_FORMAT` : backoff + footer metrics `INTERNAL_BACKOFF_METRIC_FORMAT` : backoff metrics `INTERNAL_FOOTER_METRIC_FORMAT` : footer metrics `EMPTY` : default

`fs.azure.metric.account.name`: This configuration parameter is used to specify the name of the account which will be used to push the metrics to the backend. We can configure a separate account to push metrics to the store or use the same for as the existing account on which other requests are made.

    <property>
        <name>fs.azure.metric.account.name</name>
        <value>METRICACCOUNTNAME.dfs.core.windows.net</value>
    </property>

`fs.azure.metric.account.key`: This is the access key for the storage account used for pushing metrics to the store.

    <property>
        <name>fs.azure.metric.account.key</name>
        <value>ACCOUNTKEY</value>
    </property>

`fs.azure.metric.uri`: This configuration provides the uri in the format of ‘https://`<accountname>` .dfs.core.windows.net/`<containername>`’. This should be a part of the config in order to prevent extra calls to create the filesystem. We use an existing filsystem to push the metrics.

    <property>
        <name>fs.azure.metric.uri</name>
        <value>https://METRICACCOUNTNAME.dfs.core.windows.net/CONTAINERNAME</value>
    </property>

## Troubleshooting

The problems associated with the connector usually come down to, in order

1. Classpath.
2. Network setup (proxy etc.).
3. Authentication and Authorization.
4. Anything else.

If you log `org.apache.hadoop.fs.azurebfs.services` at `DEBUG` then you will see more details about any request which is failing.

One useful tool for debugging connectivity is the cloudstore storediag utility.

This validates the classpath, the settings, then tries to work with the filesystem.

    bin/hadoop jar cloudstore-0.1-SNAPSHOT.jar storediag abfs://container@account.dfs.core.windows.net/

1. If the `storediag` command cannot work with an abfs store, nothing else is likely to.
2. If the `storediag` store does successfully work, that does not guarantee that the classpath or configuration on the rest of the cluster is also going to work, especially in distributed applications. But it is at least a start.

### `ClassNotFoundException: org.apache.hadoop.fs.azurebfs.AzureBlobFileSystem`

The `hadoop-azure` JAR is not on the classpah.

    java.lang.RuntimeException: java.lang.ClassNotFoundException:
        Class org.apache.hadoop.fs.azurebfs.AzureBlobFileSystem not found
      at org.apache.hadoop.conf.Configuration.getClass(Configuration.java:2625)
      at org.apache.hadoop.fs.FileSystem.getFileSystemClass(FileSystem.java:3290)
      at org.apache.hadoop.fs.FileSystem.createFileSystem(FileSystem.java:3322)
      at org.apache.hadoop.fs.FileSystem.access$200(FileSystem.java:136)
      at org.apache.hadoop.fs.FileSystem$Cache.getInternal(FileSystem.java:3373)
      at org.apache.hadoop.fs.FileSystem$Cache.get(FileSystem.java:3341)
      at org.apache.hadoop.fs.FileSystem.get(FileSystem.java:491)
      at org.apache.hadoop.fs.Path.getFileSystem(Path.java:361)
    Caused by: java.lang.ClassNotFoundException:
        Class org.apache.hadoop.fs.azurebfs.AzureBlobFileSystem not found
      at org.apache.hadoop.conf.Configuration.getClassByName(Configuration.java:2529)
      at org.apache.hadoop.conf.Configuration.getClass(Configuration.java:2623)
      ... 16 more

Tip: if this is happening on the command line, you can turn on debug logging of the hadoop scripts:

    export HADOOP_SHELL_SCRIPT_DEBUG=true

If this is happening on an application running within the cluster, it means the cluster (somehow) needs to be configured so that the `hadoop-azure` module and dependencies are on the classpath of deployed applications.

### `ClassNotFoundException: com.microsoft.azure.storage.StorageErrorCode`

The `azure-storage` JAR is not on the classpath.

### `Server failed to authenticate the request`

The request wasn’t authenticated while using the default shared-key authentication mechanism.

    Operation failed: "Server failed to authenticate the request.
     Make sure the value of Authorization header is formed correctly including the signature.",
     403, HEAD, https://account.dfs.core.windows.net/container2?resource=filesystem&timeout=90
      at org.apache.hadoop.fs.azurebfs.services.AbfsRestOperation.execute(AbfsRestOperation.java:135)
      at org.apache.hadoop.fs.azurebfs.services.AbfsClient.getFilesystemProperties(AbfsClient.java:209)
      at org.apache.hadoop.fs.azurebfs.AzureBlobFileSystemStore.getFilesystemProperties(AzureBlobFileSystemStore.java:259)
      at org.apache.hadoop.fs.azurebfs.AzureBlobFileSystem.fileSystemExists(AzureBlobFileSystem.java:859)
      at org.apache.hadoop.fs.azurebfs.AzureBlobFileSystem.initialize(AzureBlobFileSystem.java:110)

Causes include:

- Your credentials are incorrect.
- Your shared secret has expired. in Azure, this happens automatically
- Your shared secret has been revoked.
- host/VM clock drift means that your client’s clock is out of sync with the Azure servers —the call is being rejected as it is either out of date (considered a replay) or from the future. Fix: Check your clocks, etc.

### `Configuration property _something_.dfs.core.windows.net not found`

There’s no `fs.azure.account.key.` entry in your cluster configuration declaring the access key for the specific account, or you are using the wrong URL

    $ hadoop fs -ls abfs://container@abfswales2.dfs.core.windows.net/

    ls: Configuration property abfswales2.dfs.core.windows.net not found.

- Make sure that the URL is correct
- Add the missing account key.

### `No such file or directory when trying to list a container`

There is no container of the given name. Either it has been mistyped or the container needs to be created.

    $ hadoop fs -ls abfs://container@abfswales1.dfs.core.windows.net/

    ls: `abfs://container@abfswales1.dfs.core.windows.net/': No such file or directory

- Make sure that the URL is correct
- Create the container if needed

### “HTTP connection to https://login.microsoftonline.com/something failed for getting token from AzureAD. Http response: 200 OK”

- it has a content-type `text/html`, `text/plain`, `application/xml`

The OAuth authentication page didn’t fail with an HTTP error code, but it didn’t return JSON either

    $ bin/hadoop fs -ls abfs://container@abfswales1.dfs.core.windows.net/

     ...

    ls: HTTP Error 200;
      url='https://login.microsoftonline.com/02a07549-0a5f-4c91-9d76-53d172a638a2/oauth2/authorize'
      AADToken: HTTP connection to
      https://login.microsoftonline.com/02a07549-0a5f-4c91-9d76-53d172a638a2/oauth2/authorize
      failed for getting token from AzureAD.
      Unexpected response.
      Check configuration, URLs and proxy settings.
      proxies=none;
      requestId='dd9d526c-8b3d-4b3f-a193-0cf021938600';
      contentType='text/html; charset=utf-8';

Likely causes are configuration and networking:

1. Authentication is failing, the caller is being served up the Azure Active Directory signon page for humans, even though it is a machine calling.
2. The URL is wrong —it is pointing at a web page unrelated to OAuth2.0
3. There’s a proxy server in the way trying to return helpful instructions.

### `java.io.IOException: The ownership on the staging directory /tmp/hadoop-yarn/staging/user1/.staging is not as expected. It is owned by <principal_id>. The directory must be owned by the submitter user1 or user1`

When using Azure Managed Identities, the files/directories in ADLS Gen2 by default will be owned by the service principal object id i.e. principal ID & submitting jobs as the local OS user ‘user1’ results in the above exception.

The fix is to mimic the ownership to the local OS user, by adding the below properties to`core-site.xml`.

    <property>
      <name>fs.azure.identity.transformer.service.principal.id</name>
      <value>service principal object id</value>
      <description>
      An Azure Active Directory object ID (oid) used as the replacement for names contained
      in the list specified by “fs.azure.identity.transformer.service.principal.substitution.list”.
      Notice that instead of setting oid, you can also set $superuser here.
      </description>
    </property>
    <property>
      <name>fs.azure.identity.transformer.service.principal.substitution.list</name>
      <value>user1</value>
      <description>
      A comma separated list of names to be replaced with the service principal ID specified by
      “fs.azure.identity.transformer.service.principal.id”.  This substitution occurs
      when setOwner, setAcl, modifyAclEntries, or removeAclEntries are invoked with identities
      contained in the substitution list. Notice that when in non-secure cluster, asterisk symbol *
      can be used to match all user/group.
      </description>
    </property>

Once the above properties are configured, `hdfs dfs -ls abfs://container1@abfswales1.dfs.core.windows.net/` shows the ADLS Gen2 files/directories are now owned by ‘user1’.

## Known Issues

Following failures are known and expected to fail as of now. 1. AzureBlobFileSystem.setXAttr() and AzureBlobFileSystem.getXAttr() will fail when attempted on root (“/”) path with `Operation failed: "The request URI is invalid.", HTTP 400 Bad Request` 2. If you’re using user-delegation SAS authentication: - Listing operation for HNS accounts (on DFS endpoint) works with SAS token supporting either blob or directory scopes (Signed Resource Type as Blob or Directory), though it is intended to work only at the directory scope. It is a known bug. - AzureBlobFileSystem.getFileStatus() is expected to fail at root (“/”) path with `Operation failed: "Server failed to authenticate the request.", HTTP 401 Unauthorized Error`

## Testing ABFS

See the relevant section in Testing Azure.