Fixing a kubelet memory leak in Kubernetes 1.36

compumike•about 17 hours ago

Author here! If you're running a Kubernetes cluster, I recommend you check `kubectl version` and see if you're running "Server Version: v1.36.[0,1,2]". If so, you may want to use the one-liner at the end of the article to check your "process_resident_memory_bytes" on each node, and consider restarting kubelet as a temporary workaround to tame the memory leak until v1.36.3 is released.

CamouflagedKiwi•about 3 hours ago

Nice find.

Can't help but feel this is one of the subtle traps hidden beneath the advice that contexts aren't supposed to be stored. I know it's not always that easy, of course.

compumike•about 2 hours ago

Thanks. I know there's a `go vet` tool that's run as part of Kubernetes CI, and one of its checks is:

  lostcancel: check cancel func returned by context.WithCancel is called

I'm not 100% sure why `go vet` didn't catch this issue, but storing the cancelFn in the struct is probably part of the reason. Any Go experts know if that's the case?

cyberax•about 1 hour ago

The cancel function escapes the function body, so static analysis can't detect it. There's another lint for that (containedctx), but I think it's off in K8s.

This is a serious tripping point with Go. There's no way to express: "this is a root context that I _want_ to store and only use to create derived contexts". Goroutines are also a source of problems, you can't easily say "I'm passing the ownership of this context to a goroutine".

compumike•44 minutes ago

It does seem like a serious tripping point.

I took a quick look at "containedctx" and it seems like for this case, it would almost be backwards: it would flag the (not-memory-leaking) struct-stored "status.ctx", but wouldn't flag when there is a stored "status.cancelFn" only (which resulted in the memory leak).

Could Go implement a runtime leaked-context detector, like the data race detector? https://go.dev/doc/articles/race_detector

rirze•about 3 hours ago

Very cool. It's often daunting to contribute to such a well-established and recognizable project, but this is exactly how it should work.

__turbobrew__•about 2 hours ago

A good reason to health check the kubelet process and restart it when the checks fail.

compumike•about 2 hours ago

What kind of health checks? In my case, the kubelet process was staying alive and responsive to queries, I believe due to:

  # cat /proc/$(pgrep kubelet)/oom_score_adj
  -999
  
  (from OOMScoreAdjust=-999 in /etc/systemd/system/kubelet.service)

With this score, the Linux OOM killer wouldn't touch it, but any of my Pods were fair game.

nijave•40 minutes ago

At the metrics level, you can compare old vs new release. Have been bitten before by resource requirements dramatically change (regardless of whether it's a bug or functionality change)

fsuts•about 2 hours ago

Not all heroes wear capes! Well done

Fixing a kubelet memory leak in Kubernetes 1.36

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