[FLINK-11787] Update Kubernetes resources: workaround to make TM reachable from JM in Kubernetes

[1u0]

What is the purpose of the change

• This PR adds configuration update (Kubernetes resource definitions) as workaround for [FLINK-11127] for Flink 1.7 release branch. With this change, the TMs should be advertising themselves to JM using their k8s pods' ip addresses instead of (by default) hostnames.

NB: this patch is supposed only for Flink 1.7 release branch. Flink 1.8 and higher have introduced a new configuration option to mitigate this (taskmanager.network.bind-policy).

Brief change log

• Example Kubernetes resources are updated to use pods ip address as TMs host address

Verifying this change

This change is a trivial rework / code cleanup without any test coverage.

• Manually verified the change by running a cluser with 1 JobManagers and 2 TaskManagers in a minikube.

Does this pull request potentially affect one of the following parts:

• Dependencies (does it add or upgrade a dependency): (yes / no)
• The public API, i.e., is any changed class annotated with @Public(Evolving): (yes / no)
• The serializers: (yes / no / don't know)
• The runtime per-record code paths (performance sensitive): (yes / no / don't know)
• Anything that affects deployment or recovery: JobManager (and its components), Checkpointing, Yarn/Mesos, ZooKeeper: (yes / no / don't know)
• The S3 file system connector: (yes / no / don't know)

Documentation

• Does this pull request introduce a new feature? (yes / no)
• If yes, how is the feature documented? (not applicable / docs / JavaDocs / not documented)

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Review Progress

• ✅ 1. The [description] looks good.
  • Approved by @tillrohrmann [PMC]
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  • Approved by @tillrohrmann [PMC]
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• ✅ 4. The change fits into the overall [architecture].
  • Approved by @tillrohrmann [PMC]
• ✅ 5. Overall code [quality] is good.
  • Approved by @tillrohrmann [PMC]

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[tillrohrmann]

Thanks for opening this PR @1u0. I think we should create a separate issue for this workaround since this PR does not solve FLINK-11127 which has the goal to reverse the connection pattern of the MetricFetcher and the MetricQueryServices.

[1u0]

@tillrohrmann thanks for comment.
Yes, I agree that it doesn't address a proper fix of FLINK-11127, but just a (temporal) workaround.
I was not sure if in such cases the convention is to open an another ticket. I can create a new ticket if so.

Regarding this PR, should I close it and reopen a new one (under the new ticket) OR just update it and re-link (to the new ticket)?

[1u0]

Update: I've changed the PR title and commit message to point to the new [FLINK-11787] ticket.

[tillrohrmann]

Thanks for the fix @1u0. LGTM. Merging into release-1.7 branch.

[tillrohrmann]

@flinkbot approve all

[tillrohrmann]

Manually merged.

[tarmazakov]

Hi, thank you for this WA.

I downloaded the flink.tgz from
http://apache-mirror.rbc.ru/pub/apache/flink/flink-1.7.2/flink-1.7.2-bin-scala_2.12.tgz
that corresponding docker image flink:latest (flink:1.7)

You pass 2 args to the docker-entrypoint.sh:

args:
        - taskmanager
        - "-Dtaskmanager.host=$(K8S_POD_IP)"

But in docker-entrypoint.sh you did't pass argument -Dtaskmanager.host.. to the taskmanager.sh:
exec $(drop_privs_cmd) "$FLINK_HOME/bin/taskmanager.sh" start-foreground

Tell me how it will work?

[tillrohrmann]

The script needs to be updated to call exec $(drop_privs_cmd) "$FLINK_HOME/bin/taskmanager.sh" start-foreground "$@". Do you want to open a PR for this feature @tarmazakov.

[tarmazakov]

If you add "$@", then the taskmanager argument will be passed to taskmanager.sh, which is passed to docker-entrypoint.sh earlier. I think you need to add to the script

docker-entrypoint.sh

...
ARGS=("${@:2}")
...
elif [ "$1" = "taskmanager" ]; then
  ...
  exec $(drop_privs_cmd) "$FLINK_HOME/bin/taskmanager.sh" start-foreground "${ARGS[@]}"
fi