plugins: add tail (github.com/boz/kail)

[boz]

see boz/kail#34

Checklist for plugin developers:

• Read the Plugin Naming Guide (for new plugins)
• Verify the installation from URL or a local archive works (kubectl krew install --manifest=[...] --archive=[...])

[boz]

/assign @juanvallejo

[ahmetb]

/assign

looks like -h is failing for me on macOS

kubectl tail -h
usage: kubectl-tail [<flags>] <command> [<args> ...]

Tail for kubernetes pods

Flags:
  -h, --help                  Show context-sensitive help (also try --help-long and --help-man).
      --ignore=SELECTOR ...   ignore selector
  -l, --label=SELECTOR ...    label
  -p, --pod=NAME ...          pod
  -n, --ns=NAME ...           namespace
      --ignore-ns=NAME ...    ignore namespace
      --svc=NAME ...          service
      --rc=NAME ...           replication controller
      --rs=NAME ...           replica set
      --ds=NAME ...           daemonset
  -d, --deploy=NAME ...       deployment
      --node=NAME ...         node
      --ing=NAME ...          ingress
      --context=CONTEXT-NAME  kubernetes context
      --current-ns            use namespace from current context
  -c, --containers=NAME ...   containers
      --dry-run               print matching pods and exit
      --log-file=/dev/stderr  log file output
      --log-level=error       log level
      --since=DURATION        Display logs generated since given duration, like 5s, 2m, 1.5h or 2h45m. Defaults to 1s.panic: template: usage:30:53: executing "usage" at <
>: write /dev/stderr: resource temporarily unavailable

goroutine 1 [running]:
github.com/boz/kail/vendor/gopkg.in/alecthomas/kingpin%2ev2.(*Application).writeUsage(0xc420276000, 0xc42010b680, 0x0, 0x0)
	/home/travis/gopath/src/github.com/boz/kail/vendor/gopkg.in/alecthomas/kingpin.v2/app.go:235 +0x11b
github.com/boz/kail/vendor/gopkg.in/alecthomas/kingpin%2ev2.(*Application).maybeHelp(0xc420276000, 0xc42010b680)
	/home/travis/gopath/src/github.com/boz/kail/vendor/gopkg.in/alecthomas/kingpin.v2/app.go:249 +0xd0
github.com/boz/kail/vendor/gopkg.in/alecthomas/kingpin%2ev2.(*Application).Parse(0xc420276000, 0xc4200be010, 0x1, 0x1, 0xc420276000, 0x1d2e41b, 0x7, 0x1d3a53b)
	/home/travis/gopath/src/github.com/boz/kail/vendor/gopkg.in/alecthomas/kingpin.v2/app.go:213 +0x18a
github.com/boz/kail/vendor/gopkg.in/alecthomas/kingpin%2ev2.Parse(0x1d2e41b, 0x7)
	/home/travis/gopath/src/github.com/boz/kail/vendor/gopkg.in/alecthomas/kingpin.v2/global.go:37 +0x77
main.main()
	/home/travis/gopath/src/github.com/boz/kail/cmd/kail/main.go:97 +0x121

[boz]

Thanks @ahmetb. Fixed in v0.9.1.

/assign @ahmetb

[ahmetb]

/cc @corneliusweig

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[corneliusweig]

Thanks for your contribution!

Please also add a caveats field. It is shown post-install which gives you the opportunity to show

• how your tool is invoked
• where to find usage instructions

---

When I run tail (linux,amd64) and end it with Ctrl+C, it gives the following error:

E0517 11:42:07.325821   20111 streamwatcher.go:109] Unable to decode an event from the watch stream: context canceled

Is that expected behavior?

[boz]

Thanks for the feedback @corneliusweig. I'll address these things when I have a chance.

E0517 11:42:07.325821 20111 streamwatcher.go:109] Unable to decode an event from the watch stream: context canceled
Is that expected behavior?

It's from glog somewhere inside k8s.io/{client-go,apimachinery,etc...}. I tried to suppress these but apparently they're still showing up.

I don't see them when I run kail by itself. Is kubectl adding glog configuration? Does your environment have glog settings?

Anyways... it's somewhat expected because a context is indeed cancelled to shut things down, but of course ideally the message wouldn't be shown 🤷‍♂️

[corneliusweig]

@boz I haven't checked where exactly the error is logged. But if you have it under control, do you already do a check like

if err ! = nil && ctx.Err() == context.Cancelled { return nil } 

(beware, typed on phone)

[ahmetb]

If you’re seeing some weird behavior when process ran as a plugin vs standalone, this is totally worth filing a bug to kubectl.
Plugins are executed with execve(2) syscall, which would replace the kubectl process with your executable, so it shouldn't behave differently than running your executable standalone.

[boz]

@boz I haven't checked where exactly the error is logged. But if you have it under control, do you already do a check like
[snip]

I don't use glog. I'm... not a fan ;)

[snip]
Plugins are executed with execve(2) syscall, which would replace the kubectl process with your executable, so it shouldn't behave differently than running your executable standalone.

I don't know of any other way of executing new programs. It could still be that kubectl is adding environment variables that govern glog behavior.

It could be a lot of things, tho - including recent changes to kail. I'll look into it when I have a chance. I'm also in the middle of bumping the k8s lib dependencies, which might resolve the issue.

@corneliusweig, @ahmetb: thanks for the help!

[ahmetb]

OK no rush. Let’s hold until the issue is fixed.
/hold

[boz]

Looks like glog has been removed from k8s.io libs 🎊 🎊 🎊

I've updated the various manifest fields and bumped to a version of kail that uses up-to-date k8s.io libs. Let me know what you guys think.

[corneliusweig]

Looks like some examples in the caveats section are duplicated. I think three are fine anyway.

[boz]

bump @ahmetb

[ahmetb]

Sorry just got back from kubecon!

The only problem I'm seeing so far is a discrepancy with the potential style guide we'll be adding (#152): kail uses --ns flag whereas the recommended Kubernetes guideline is to use -n/--namespace (via git.k8s.io/cli-runtime).

But I think we can make an exception since the tool was existing before and has a broad user base that is not easy to break. @corneliusweig any input?

[boz]

Right on.

FWIW -n NAMESPACE works and --namespace NAMESPACE can be added. Note that the default is all namespaces sans kube-system; this can be overridden with --current-ns or KAIL_CURRENT_NS=true.

If it's a huge problem, adding cmd/kubectl-tail next to cmd/kail that conforms to some standard set of flags/behaviors is doable but something I'd like to avoid if at all possible.

[ahmetb]

SG. I guess you can add —namespace later.
/lgtm
/approve

We don’t strictly enforce the flags etc for now. So I think we can have this.

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[ahmetb]

/hold cancel

[corneliusweig]

Sorry, for being so slow to respond.

I think it would be a great idea to also add --namespace. Having --ns in addition won't hurt anyone, but conforming to the k8s standard -n/--namespace is in general a good idea. I opened boz/kail#38 so it is tracked.