Running Spark Applications on YARN

In YARN, each application instance has an ApplicationMaster process, which is the first container started for that application. The application is responsible for requesting resources from the ResourceManager. Once the resources are allocated, the application instructs NodeManagers to start containers on its behalf. ApplicationMasters eliminate the need for an active client: the process starting the application can terminate, and coordination continues from a process managed by YARN running on the cluster.

For the option to specify the deployment mode, see spark-submit Options.

Cluster Deployment Mode

In cluster mode, the Spark driver runs in the ApplicationMaster on a cluster host. A single process in a YARN container is responsible for both driving the application and requesting resources from YARN. The client that launches the application does not need to run for the lifetime of the application.

Cluster mode is not well suited to using Spark interactively. Spark applications that require user input, such as spark-shell and pyspark, require the Spark driver to run inside the client process that initiates the Spark application.

Client Deployment Mode

In client mode, the Spark driver runs on the host where the job is submitted. The ApplicationMaster is responsible only for requesting executor containers from YARN. After the containers start, the client communicates with the containers to schedule work.

Deployment Mode Summary

Mode	YARN Client Mode	YARN Cluster Mode
Driver runs in	Client	ApplicationMaster
Requests resources	ApplicationMaster	ApplicationMaster
Starts executor processes	YARN NodeManager	YARN NodeManager
Persistent services	YARN ResourceManager and NodeManagers	YARN ResourceManager and NodeManagers
Supports Spark Shell	Yes	No

Spark requires that the HADOOP_CONF_DIR or YARN_CONF_DIR environment variable point to the directory containing the client-side configuration files for the cluster. These configurations are used to write to HDFS and connect to the YARN ResourceManager. If you are using a Cloudera Manager deployment, these variables are configured automatically. If you are using an unmanaged deployment, ensure that you set the variables as described in Running Spark on YARN.

To run the spark-shell or pyspark client on YARN, use the --master yarn --deploy-mode client flags when you start the application.

If you are using a Cloudera Manager deployment, these properties are configured automatically.

To submit an application to YARN, use the spark-submit script and specify the --master yarn flag. For other spark-submit options, see spark-submit Arguments.

To obtain information about Spark application behavior you can consult YARN logs and the Spark web application UI. These two methods provide complementary information. For information how to view logs created by Spark applications and the Spark web application UI, see Monitoring Spark Applications.

These examples demonstrate how to use spark-submit to submit the SparkPi Spark example application with various options. In the examples, the argument passed after the JAR controls how close to pi the approximation should be.

In a CDH deployment, SPARK_HOME defaults to /usr/lib/spark in package installations and /opt/cloudera/parcels/CDH/lib/spark in parcel installations. In a Cloudera Manager deployment, the shells are also available from /usr/bin.

In addition to spark-submit Options, options for running Spark applications on YARN are listed in spark-submit on YARN Options.

During initial installation, Cloudera Manager tunes properties according to your cluster environment.

In addition to the command-line options, the following properties are available:

Dynamic allocation allows Spark to dynamically scale the cluster resources allocated to your application based on the workload. When dynamic allocation is enabled and a Spark application has a backlog of pending tasks, it can request executors. When the application becomes idle, its executors are released and can be acquired by other applications.

Starting with CDH 5.5, dynamic allocation is enabled by default. Dynamic Allocation Properties describes properties to control dynamic allocation.

If you set spark.dynamicAllocation.enabled to false or use the --num-executors command-line argument or set the spark.executor.instances property when running a Spark application, dynamic allocation is disabled. For more information on how dynamic allocation works, see resource allocation policy.

When Spark dynamic resource allocation is enabled, all resources are allocated to the first submitted job available causing subsequent applications to be queued up. To allow applications to acquire resources in parallel, allocate resources to pools and run the applications in those pools and enable applications running in pools to be preempted. See Dynamic Resource Pools.

If you are using Spark Streaming, see the recommendation in Spark Streaming and Dynamic Allocation.

In CDH deployments not managed by Cloudera Manager, Spark copies the Spark assembly JAR file to HDFS each time you run spark-submit. You can avoid this copying by doing one of the following:

• Set spark.yarn.jar to the local path to the assembly JAR: local:/usr/lib/spark/lib/spark-assembly.jar.
• Upload the JAR and configure the JAR location:
  1. Manually upload the Spark assembly JAR file to HDFS:

     $ hdfs dfs -mkdir -p /user/spark/share/lib
     $ hdfs dfs -put SPARK_HOME/assembly/lib/spark-assembly_*.jar /user/spark/share/lib/spark-assembly.jar

     You must manually upload the JAR each time you upgrade Spark to a new minor CDH release.
  2. Set spark.yarn.jar to the HDFS path:

     spark.yarn.jar=hdfs://namenode:8020/user/spark/share/lib/spark-assembly.jar