Provide a way to retrieve logs for previous pod instances (similar to --previous option on kubectl)

[longwa]

Kubectl allows for the --previous option to logs to view previous instance of the logs.

You can use kubectl logs to retrieve logs from a previous instantiation of a container with --previous flag, in case the container has crashed. If your pod has multiple containers, you should specify which container's logs you want to access by appending a container name to the command. See the kubectl logs documentation for more details

I can't seem to find a way to do that in the fabric8 API.

Also, I'm not sure how to retrieve logs for a specific container within the pod in cases where there are multiple. Maybe this exists in the API, but I can't find an example of how to do it.

[rohanKanojia]

Do you know what api is hit behind the scenes with --previous? Could you please share output of kubectl logs --previous pod/your-pod -v=8?

For latter part, Could you please check if this works for you?

kubernetes-client/kubernetes-tests/src/test/java/io/fabric8/kubernetes/client/mock/PodTest.java

Lines 286 to 290 in 653c79e

	log = client.pods().withName("pod3").inContainer("cnt3").getLog();
	assertEquals(pod3Log, log);
	log = client.pods().inNamespace("test4").withName("pod4").inContainer("cnt4").withPrettyOutput().getLog();
	assertEquals(pod4Log, log);

[longwa]

Looks like it just passes the previous=true:

I0818 19:57:11.540778   81327 round_trippers.go:420] GET https://<ip>:6443/api/v1/namespaces/playarea-52688c/pods/tcs-6db8ff5bbc-fqzlg/log?previous=true
I0818 19:57:11.540802   81327 round_trippers.go:427] Request Headers:
I0818 19:57:11.540807   81327 round_trippers.go:431]     Accept: application/json, */*
I0818 19:57:11.540810   81327 round_trippers.go:431]     User-Agent: kubectl/v1.18.2 (darwin/amd64) kubernetes/52c56ce
I0818 19:57:11.587698   81327 round_trippers.go:446] Response Status: 200 OK in 46 milliseconds
I0818 19:57:11.587727   81327 round_trippers.go:449] Response Headers:
I0818 19:57:11.587731   81327 round_trippers.go:452]     Cache-Control: no-cache, private
I0818 19:57:11.587734   81327 round_trippers.go:452]     Content-Type: text/plain
I0818 19:57:11.587738   81327 round_trippers.go:452]     Date: Tue, 18 Aug 2020 23:57:11 GMT

Not sure the best approach, I guess either adding a getPreviousLog() method or maybe a boolean (previous = true) for the getLog() method (it already has pretty print option).

I'll try the specific container approach, I didn't realize that inContainer method existed. Thanks!

[rohanKanojia]

Sorry, I think I said we don't support it without checking. I checked the code and seems like this flag is being passed:

kubernetes-client/kubernetes-client/src/main/java/io/fabric8/kubernetes/client/dsl/internal/core/v1/PodOperationsImpl.java

Lines 159 to 161 in a007adf

	if (withTerminatedStatus) {
	sb.append("&previous=true");
	}

I think this should do the trick for you:

client.pods().inNamespace(namespace).withName("test-pod1").terminated().getLog();

[rohanKanojia]

The only thing we're missing is adding some documentation about these supported flags

[longwa]

Thanks, that's what I was looking for, just didn't see it initially.

[rohanKanojia]

@longwa : No worries. I think one of the main problems in this project is that there is not much documentation present for users. I'll try adding documentation for Pod log options here: https://github.com/fabric8io/kubernetes-client/blob/master/doc/CHEATSHEET.md

[longwa]

@rohanKanojia Most of the API is very intuitive and easy to discover. It's is much easier to use than the official client.

[rohanKanojia]

@longwa : Thanks a lot for your feedback. I also think our API is more friendly to java developers(I used to think I was biased 🙄 )