client-go/transport: fix memory leak when using rest.Config Dial function

[lizardruss]

What type of PR is this?

/kind bug

What this PR does / why we need it:

When using a rest.Config Dial function and constructing a client with client.New() or kubernetes.NewForConfig(), the tlsConfigCache is ineffective because the Dial function is wrapped in a new DialHolder instance every time. This leads to a memory leak since the tlsConfigCache grows unbounded with unique keys. This change allows skipping the tlsConfigCache for this case.

Which issue(s) this PR fixes:

Fixes #118703

Special notes for your reviewer:

Here are graphs showing the change in memory usage before & after this fix. I have marked this as not having a user facing change, since unless the user has taken care to reuse DialHolder instances when creating clients, they would not have seen the benefits of the tlsConfigCache.

before

after

Does this PR introduce a user-facing change?

NONE

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

[k8s-ci-robot]

Welcome @lizardruss!

It looks like this is your first PR to kubernetes/kubernetes 🎉. Please refer to our pull request process documentation to help your PR have a smooth ride to approval.

You will be prompted by a bot to use commands during the review process. Do not be afraid to follow the prompts! It is okay to experiment. Here is the bot commands documentation.

You can also check if kubernetes/kubernetes has its own contribution guidelines.

You may want to refer to our testing guide if you run into trouble with your tests not passing.

If you are having difficulty getting your pull request seen, please follow the recommended escalation practices. Also, for tips and tricks in the contribution process you may want to read the Kubernetes contributor cheat sheet. We want to make sure your contribution gets all the attention it needs!

Thank you, and welcome to Kubernetes. 😃

[k8s-ci-robot]

Hi @lizardruss. 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.

Once the patch is verified, the new status will be reflected by the ok-to-test label.

I understand the commands that are listed here.

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes-sigs/prow repository.

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: lizardruss
Once this PR has been reviewed and has the lgtm label, please assign smarterclayton for approval. For more information see the Kubernetes Code Review Process.

The full list of commands accepted by this bot can be found here.

Needs approval from an approver in each of these files:

• staging/src/k8s.io/client-go/OWNERS

Approvers can indicate their approval by writing /approve in a comment
Approvers can cancel approval by writing /approve cancel in a comment

[seans3]

/ok-to-test

[liggitt]

/assign @enj

[k8s-ci-robot]

@lizardruss: The following tests failed, say /retest to rerun all failed tests or /retest-required to rerun all mandatory failed tests:

Test name	Commit	Details	Required	Rerun command
pull-kubernetes-verify	74ff449	link	true	/test pull-kubernetes-verify
pull-kubernetes-e2e-gce	74ff449	link	true	/test pull-kubernetes-e2e-gce

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.

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes-sigs/prow repository. I understand the commands that are listed here.

[aojea]

I didn't check in detail, is this related ot this #117258, we have added some metrics to have more visibility into these problems #117295, @lizardruss just curiosity, do you know if the metrics are useful in this case ?

[enj]

I think the problem with all of these types of changes is that they make assumptions about how the caller was using this code. A caller of this method could be re-using the return value, meaning they would correctly be getting the TLS cache benefits, which this PR would now disable. We allow for infinite flexibility, so every change has the potential to break someone in a subtle way.

[lizardruss]

I agree with your perspective, and originally I wanted to expose the DialHolder on the rest.Config struct, however that is a larger change. It would provide a more intentional way of re-using the DialHolder when the caching behavior is expected.

As things exist now, unless the caller takes care to re-use the returned DialHolder, it's not obvious that a memory leak occurs when the Dial function is configured. The places we most often encounter this issue are client.New() and kubernetes.NewForConfig(), which make re-using the DialHolder non-obvious.

[cici37]

/triage accepted