# Configure applications
<a name="emr-configure-apps"></a>

To override the default configurations for an application, you can supply a configuration object. You can either use a shorthand syntax to provide the configuration, or you can reference the configuration object in a JSON file. Configuration objects consist of a classification, properties, and optional nested configurations. Properties correspond to the application settings you want to change. You can specify multiple classifications for multiple applications in a single JSON object.

**Warning**  
Amazon EMR Describe and List API operations emit custom and configurable settings, which are used as a part of Amazon EMR job flows, in plaintext. To provide sensitive information, such as passwords, in these settings, see [Store sensitive configuration data in AWS Secrets Manager](https://docs.aws.amazon.com/emr/latest/ReleaseGuide/storing-sensitive-data.html).

The configuration classifications that are available vary by Amazon EMR release version. For a list of configuration classifications that are supported in a particular release version, refer to the page for that release version under [About Amazon EMR Releases](emr-release-components.md).

The following is example JSON file for a list of configurations.

```
[
  {
    "Classification": "core-site",
    "Properties": {
      "hadoop.security.groups.cache.secs": "250"
    }
  },
  {
    "Classification": "mapred-site",
    "Properties": {
      "mapred.tasktracker.map.tasks.maximum": "2",
      "mapreduce.map.sort.spill.percent": "0.90",
      "mapreduce.tasktracker.reduce.tasks.maximum": "5"
    }
  }
]
```

A configuration classification often maps to an application-specific configuration file. For example, the `hive-site` classification maps to settings in the `hive-site.xml` configuration file for Hive. An exception to this is the no longer supported bootstrap action `configure-daemons`, which is used to set environment parameters such as `--namenode-heap-size`. Options like this are subsumed into the `hadoop-env` and `yarn-env` classifications with their own nested export classifications. If any classification ends in `env`, use the export sub-classification. 

Another exception is `s3get`, which is used to place a customer `EncryptionMaterialsProvider` object on each node in a cluster for use in client-side encryption. An option was added to the `emrfs-site` classification for this purpose.

The following is an example of the `hadoop-env` classification.

```
[
  {
    "Classification": "hadoop-env",
    "Properties": {
      
    },
    "Configurations": [
      {
        "Classification": "export",
        "Properties": {
          "HADOOP_DATANODE_HEAPSIZE": "2048",
          "HADOOP_NAMENODE_OPTS": "-XX:GCTimeRatio=19"
        },
        "Configurations": [
          
        ]
      }
    ]
  }
]
```

The following is an example of the yarn-env classification.

```
[
  {
    "Classification": "yarn-env",
    "Properties": {
      
    },
    "Configurations": [
      {
        "Classification": "export",
        "Properties": {
          "YARN_RESOURCEMANAGER_OPTS": "-Xdebug -Xrunjdwp:transport=dt_socket"
        },
        "Configurations": [
          
        ]
      }
    ]
  }
]
```

The following settings do not belong to a configuration file but are used by Amazon EMR to potentially configure multiple settings on your behalf.


**Settings curated by Amazon EMR**  

| Application | Release label classification | Valid properties | When to use | 
| --- | --- | --- | --- | 
| Spark | spark | maximizeResourceAllocation | Configure executors to utilize the maximum resources of each node. | 

**Topics**
+ [Configure applications when you create a cluster](emr-configure-apps-create-cluster.md)
+ [Reconfigure an instance group in a running cluster](emr-configure-apps-running-cluster.md)
+ [Store sensitive configuration data in AWS Secrets Manager](storing-sensitive-data.md)
+ [Configure applications to use a specific Java Virtual Machine](configuring-java8.md)