ability to run a local command with port-forward

[carlory]

What type of PR is this?

/kind feature

What this PR does / why we need it:

This would allow scripting around port-forwarding. That will be especially useful for developers, but can also be useful in production. Currently, we can do that, but we have to use one terminal to create the port-forwarding, use another to run any tool that uses the port, then finally go back to the first terminal and terminate the forwarding. This is not scriptable.

Which issue(s) this PR fixes:

Fixes #97549

Special notes for your reviewer:

Does this PR introduce a user-facing change?:

Support exec in `kubectl port-forward`. For example, kubectl port-forward service/postgres 5432 -- psql -h localhost -p 5432 -c "select 1"

Additional documentation e.g., KEPs (Kubernetes Enhancement Proposals), usage docs, etc.:

[k8s-ci-robot]

@carlory: This issue is currently awaiting triage.

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[k8s-ci-robot]

Hi @carlory. Thanks for your PR.

I'm waiting for a kubernetes member to verify that this patch is reasonable to test. If it is, they should reply with /ok-to-test on its own line. Until that is done, I will not automatically test new commits in this PR, but the usual testing commands by org members will still work. Regular contributors should join the org to skip this step.

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[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: carlory
To complete the pull request process, please assign deads2k after the PR has been reviewed.
You can assign the PR to them by writing /assign @deads2k in a comment when ready.

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[carlory]

Example:

➜  kubernetes git:(feature-kubectl-port-forward) ✗ _output/bin/kubectl  port-forward backend-mysql-55c8958756-b6sh2 3306 -- mysql -h 127.0.0.1 -uroot -p
Forwarding from 127.0.0.1:3306 -> 3306
Forwarding from [::1]:3306 -> 3306
Enter password:
Handling connection for 3306
Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is 18
Server version: 5.7.22 MySQL Community Server (GPL)

Copyright (c) 2000, 2020, Oracle and/or its affiliates. All rights reserved.

Oracle is a registered trademark of Oracle Corporation and/or its
affiliates. Other names may be trademarks of their respective
owners.

Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.

mysql> show databases;
+--------------------+
| Database           |
+--------------------+
| information_schema |
| mysql              |
| performance_schema |
| sys                |
+--------------------+
6 rows in set (0.21 sec)

mysql> exit
Bye

[carlory]

/assign @deads2k @FranciscoKurpiel

[k8s-ci-robot]

@carlory: GitHub didn't allow me to assign the following users: FranciscoKurpiel.

Note that only kubernetes members, repo collaborators and people who have commented on this issue/PR can be assigned. Additionally, issues/PRs can only have 10 assignees at the same time.
For more information please see the contributor guide

In response to this:

/assign @deads2k @FranciscoKurpiel

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[FranciscoKurpiel]

@carlory, while trying your PR I come up with a few considerations regarding the standard streams (stdin/oiut/err). I described the considerations here the original ticket, so that they can be taken into consideration for the consideration on sig.

edit: durp!

[carlory]

@FranciscoKurpiel

Thanks for your guide. It is a good idea. I will try to implement it this week.

[carlory]

@FranciscoKurpiel suppress kubectl is implemented.

case 1:

➜  kubernetes git:(feature-kubectl-port-forward) ./_output/bin/kubectl port-forward -q backend-mysql-55c8958756-b6sh2 3306 -- mysql -h 127.0.0.1 -uroot -pdangerous -e "select version();"
mysql: [Warning] Using a password on the command line interface can be insecure.
+-----------+
| version() |
+-----------+
| 5.7.22    |
+-----------+

case 2:

➜  kubernetes git:(feature-kubectl-port-forward) ./_output/bin/kubectl port-forward -q backend-mysql-55c8958756-b6sh2 3306 -- mysql -h 127.0.0.1 -uroot -pdangerous -e "select version();" > /tmp/out.log 2> /tmp/err.log

➜  kubernetes git:(feature-kubectl-port-forward) cat /tmp/out.log
version()
5.7.22

➜  kubernetes git:(feature-kubectl-port-forward) cat /tmp/err.log
mysql: [Warning] Using a password on the command line interface can be insecure.

case 3:

➜  kubernetes git:(feature-kubectl-port-forward) ./_output/bin/kubectl port-forward -q backend-mysql-55c8958756-b6sh2 3306 -- mysql -h 127.0.0.1 -uroot -pdangerous -e "select version();" 2> /tmp/err.log | grep -v "version"
5.7.22

➜  kubernetes git:(feature-kubectl-port-forward) ./_output/bin/kubectl port-forward -q backend-mysql-55c8958756-b6sh2 3306 -- mysql -h 127.0.0.1 -uroot -pdangerous -e "select version();" | grep -v "version"
mysql: [Warning] Using a password on the command line interface can be insecure.
5.7.22

[carlory]

There is still a problem to be considered here.

If during the execution of the local command, the goroutine responsible for forwarding the network traffic exits suddenly, immediately returns the error of the goroutine, and exit the executing command, is it really reasonable?

go func() {
 	errChan <- o.PortForwarder.ForwardPorts("POST", req.URL(), o)
 }()

It may be a good idea to only print the port-forwarder error to stderr without interrupting the execution of the local command.

@FranciscoKurpiel Any ideas about it?

[FranciscoKurpiel]

If during the execution of the local command, the goroutine responsible for forwarding the network traffic exits suddenly, immediately returns the error of the goroutine, and exit the executing command, is it really reasonable?

That should be handled a broken pipe, we should send a SIGPIPE. Unfortunately there might be some platform-specific details there.

I'm just a bit worried with the fact that we are moving quite a lot before the ticket being accepted or discussed on the sig. I provided the ticket and I'm providing my input, but the actual specification will come from the special group.

[carlory]

/ok-to-test

[k8s-ci-robot]

@carlory: Cannot trigger testing until a trusted user reviews the PR and leaves an /ok-to-test message.

In response to this:

/ok-to-test

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[carlory]

/ok-to-test

[carlory]

/test pull-kubernetes-bazel-test

[carlory]

/retest

[k8s-ci-robot]

@carlory: The following tests failed, say /retest to rerun all failed tests:

Test name	Commit	Details	Rerun command
pull-kubernetes-bazel-test	71b4994	link	/test pull-kubernetes-bazel-test
pull-kubernetes-verify	71b4994	link	/test pull-kubernetes-verify
pull-kubernetes-bazel-build	71b4994	link	/test pull-kubernetes-bazel-build

Full PR test history. Your PR dashboard. Please help us cut down on flakes by linking to an open issue when you hit one in your PR.

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[fejta-bot]

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