TakawaAkirayo created SPARK-47951:
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             Summary: Support retrieving the real SparkConnectService GRPC 
address and port programmatically when running on Yarn
                 Key: SPARK-47951
                 URL: https://issues.apache.org/jira/browse/SPARK-47951
             Project: Spark
          Issue Type: Story
          Components: Connect
    Affects Versions: 4.0.0
            Reporter: TakawaAkirayo


1. {*}User Story{*}:
Our data analysts and data scientists use Jupyter notebooks provisioned on 
Kubernetes (k8s) with limited CPU/memory resources to run Spark-shell/pyspark 
in the terminal via Yarn Client mode.
However, Yarn Client mode consumes significant local memory if the job is 
heavy, and the total resource pool of k8s for notebooks is limited.
To leverage the abundant resources of our Hadoop cluster for scalability 
purposes, we aim to utilize SparkConnect.
This allows the driver on Yarn with SparkConnectService started and uses 
SparkConnect client to connect to the remote driver.

To provide a seamless experience with one command startup for both server and 
client, we've wrapped the following processes in one script:

1). Start a local coordinator server (implemented by us internally, not in this 
PR) in the host of jupyter notebook.
2). Start SparkConnectServer by spark-submit via Yarn Cluster mode with 
user-input Spark configurations and the local coordinator server's address and 
port.
    Append an additional listener class in the configuration for 
SparkConnectService callback with the actual address and port on Yarn to the 
coordinator server.
3). Wait for the coordinator server to receive the address callback from the 
SparkConnectService on Yarn and export the real address.
4). Start the client (pyspark --remote $callback_address) with the remote 
address.

2. {*}Problem statement of this change{*}:
1). The specified port for the SparkConnectService GRPC server might be 
occupied on the node of the Hadoop Cluster.
    To increase the success rate of startup, it needs to retry on conflicts 
rather than fail directly.
2). Because the final binding port could be uncertain based on #1 when retry 
and the remote address is unpredictable on Yarn,
    we need to retrieve the address and port programmatically and inject it 
automatically on the start of `pyspark --remote`.
    To get the address of SparkConnectService on Yarn programmatically, The 
SparkConnectService needs to communicate its location back to the launcher side.



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