[ZEPPELIN-6143] Add Interpreter Event Server Port configuration option

[tbonelee]

What is this PR for?

This PR introduces the ZEPPELIN_EVENT_SERVER_PORT configuration option.
When this option is set, the Event server that communicates with interpreters will listen on the specified port.

The ZEPPELIN_EVENT_SERVER_PORT option takes precedence over ZEPPELIN_SERVER_RPC_PORTRANGE option.
If ZEPPELIN_EVENT_SERVER_PORT is set, the ZEPPELIN_SERVER_RPC_PORTRANGE range will be ignored.

This option is particularly useful when running individual Zeppelin components in container orchestration environments like Kubernetes.
By explicitly specifying the port, it allows for a more declarative and clearer configuration of service resources compared to ZEPPELIN_SERVER_RPC_PORTRANGE.

What type of PR is it?

Improvement

Todos

• - Task

What is the Jira issue?

• Open an issue on Jira https://issues.apache.org/jira/browse/ZEPPELIN-6143

How should this be tested?

• Run Zeppelin with and without this configuration and check zeppelin-server logs for the message "InterpreterEventServer is starting at ". Verify that the specified port is used as intended(If the option is set).

Questions:

• Does the license files need to update? No
• Is there breaking changes for older versions? No
• Does this needs documentation? Yes

[Reamer]

I understand your approach. Currently I use the ZEPPELIN_SERVER_RPC_PORTRANGE 12320:12320 in my K8s landscape to configure a K8s-Service cleanly.
Why did you decide on the name ZEPPELIN_EVENT_SERVER_PORT, wouldn't ZEPPELIN_SERVER_RPC_PORT be better?

[tbonelee]

@Reamer
I considered both ZEPPELIN_EVENT_SERVER_PORT and ZEPPELIN_SERVER_RPC_PORT. I chose the former because the term "SERVER" in the latter could be too general, making it unclear which server it refers to, and ZEPPELIN_SERVER_RPC_PORT may be easily confused with ZEPPELIN_SERVER_RPC_PORTRANGE due to the similarity in names.

However, aligning with previous variable names might improve predictability as well, which is why I didn't have a strong preference for the former option from the beginning. What do you think?

[Reamer]

I favor ZEPPELIN_SERVER_RPC_PORT. Can you remove portRange as a class variable of RemoteInterpreterEventServer and perform the evaluation of the port or portrange in the start()-method.
Furthermore, I do not see any documentation for ZEPPELIN_SERVER_RPC_PORTRANGE you can also add it near the documentation for ZEPPELIN_SERVER_RPC_PORT .

[tbonelee]

@Reamer Thanks for the feedback. I've added some commits based on your suggestions:

• Renamed the ZEPPELIN_EVENT_SERVER_PORT variable to ZEPPELIN_SERVER_RPC_PORT.
• Removed portRange variable from RemoteInterpreterEventServer.
• Added documentation for the ZEPPELIN_SERVER_RPC_PORTRANGE and ZEPPELIN_INTERPRETER_RPC_PORTRANGE variables.