---
title: Configuration
layout: documentation
documentation: true
---
Storm has a variety of configurations for tweaking the behavior of nimbus, supervisors, and running topologies. Some configurations are system configurations and cannot be modified on topology by topology basis, whereas other configurations can be modified per topology. 

Every configuration has a default value defined in [defaults.yaml]({{page.git-blob-base}}/conf/defaults.yaml) in the Storm codebase. You can override these configurations by defining a storm.yaml in the classpath of Nimbus and the supervisors. Finally, you can define a topology-specific configuration that you submit along with your topology when using [StormSubmitter](https://javadoc.io/doc/org.apache.storm/storm-client/2.8.8/org/apache/storm/StormSubmitter.html). However, the topology-specific configuration can only override configs prefixed with "TOPOLOGY".

Storm 0.7.0 and onwards lets you override configuration on a per-bolt/per-spout basis. The only configurations that can be overridden this way are:

1. "topology.debug"
2. "topology.max.spout.pending"
3. "topology.max.task.parallelism"
4. "topology.kryo.register": This works a little bit differently than the other ones, since the serializations will be available to all components in the topology. More details on [Serialization](Serialization.html). 

The Java API lets you specify component specific configurations in two ways:

1. *Internally:* Override `getComponentConfiguration` in any spout or bolt and return the component-specific configuration map.
2. *Externally:* `setSpout` and `setBolt` in `TopologyBuilder` return an object with methods `addConfiguration` and `addConfigurations` that can be used to override the configurations for the component.

The preference order for configuration values is defaults.yaml < storm.yaml < topology specific configuration < internal component specific configuration < external component specific configuration. 

# Bolts, Spouts, and Plugins
In almost all cases configuration for a bolt or a spout should be done through setters on the bolt or spout implementation and not the topology conf.  In some rare cases, it may make sense to
expose topology wide configurations that are not currently a part of [Config](https://javadoc.io/doc/org.apache.storm/storm-client/2.8.8/org/apache/storm/Config.html) or [DaemonConfig](https://javadoc.io/doc/org.apache.storm/storm-client/2.8.8/org/apache/storm/DaemonConfig.html) such as
when writing a custom scheduler or a plugin to some part of storm.  In those
cases you can create your own class like Config but implements [Validated](https://javadoc.io/doc/org.apache.storm/storm-client/2.8.8/org/apache/storm/validation/Validated.html). Any `public static final String` field declared in this
class will be treated as a config and annotations from the `org.apache.storm.validation.ConfigValidationAnnotations` class can be used to enforce what is stored in that config.
To let the validator know about this class you need to treat the class
like a service that will be loaded through a ServiceLoader for the Validated class and include a `META-INF/services/org.apache.storm.validation.Validated` file in your jar that holds
the name of your Config class.

**Resources:**

* [Config](https://javadoc.io/doc/org.apache.storm/storm-client/2.8.8/org/apache/storm/Config.html): a listing of client configurations as well as a helper class for creating topology specific configurations
* [DaemonConfig](https://javadoc.io/doc/org.apache.storm/storm-client/2.8.8/org/apache/storm/DaemonConfig.html): a listing of Storm Daemon configurations.
* [defaults.yaml]({{page.git-blob-base}}/conf/defaults.yaml): the default values for all configurations
* [Setting up a Storm cluster](Setting-up-a-Storm-cluster.html): explains how to create and configure a Storm cluster
* [Running topologies on a production cluster](Running-topologies-on-a-production-cluster.html): lists useful configurations when running topologies on a cluster
* [Local mode](Local-mode.html): lists useful configurations when using local mode
