When run SparkSubmit --class [mainClass], SparkSubmit will call a childMainClass which is
1. client mode, childMainClass = mainClass
2. standalone cluster mde, childMainClass = org.apache.spark.deploy.Client
3. yarn cluster mode, childMainClass = org.apache.spark.deploy.yarn.Client
The childMainClass is a wrapper of mainClass. The childMainClass will be called in SparkSubmit, and if cluster mode, the childMainClass will talk to the the cluster and launch a process on one woker to run the mainClass.
ps. use "spark-submit -v" to print debug infos.
Yarn client: spark-submit -v --class "org.apache.spark.examples.JavaWordCount" --master yarn JavaWordCount.jar
childMainclass: org.apache.spark.examples.JavaWordCount
Yarn cluster: spark-submit -v --class "org.apache.spark.examples.JavaWordCount" --master yarn-cluster JavaWordCount.jar
childMainclass: org.apache.spark.deploy.yarn.Client
Standalone client: spark-submit -v --class "org.apache.spark.examples.JavaWordCount" --master spark://aa01:7077 JavaWordCount.jar
childMainclass: org.apache.spark.examples.JavaWordCount
Stanalone cluster: spark-submit -v --class "org.apache.spark.examples.JavaWordCount" --master spark://aa01:7077 --deploy-mode cluster JavaWordCount.jar
childMainclass: org.apache.spark.deploy.rest.RestSubmissionClient (if rest, else org.apache.spark.deploy.Client)
Taking standalone spark as example, here is the client mode workflow. The mainclass run in the driver application which could be reside out of the cluster.
On cluster mode showed as below, SparkSubmit will register driver in the cluster, and a driver process launched in one work running the main class.
There are also two deploy modes that can be used to launch Spark applications on YARN. In yarn-cluster mode, the Spark driver runs inside an application master process which is managed by YARN on the cluster, and the client can go away after initiating the application. In yarn-client mode, the driver runs in the client process, and the application master is only used for requesting resources from YARN.
Cluster deploy mode is not applicable to Spark shells.