Add info about mirror pods in FAQ

[vadasambar]

We use the wording mirror pods in our flags but don't really talk about what they mean anywhere. e.g.,

More can be found in the FAQ here
This can be confusing for end users.

[vadasambar]

/kind documentation

[vadasambar]

kind/bug is not correct here but I am not sure how to remove it yet.

[gregth]

Maybe a reference to the Kubernetes documentation would help: https://kubernetes.io/docs/tasks/configure-pod-container/static-pod/

[Shubham82]

/remove-kind bug

[Shubham82]

Maybe a reference to the Kubernetes documentation would help: https://kubernetes.io/docs/tasks/configure-pod-container/static-pod/

It seems good!
I'm up for it.

[Shubham82]

/assign

[Shubham82]

Fixed it here: #5609

[vadasambar]

@Shubham82 thanks for picking this up. Note that we have some additional TODOs:

From the comment here

1. add link to official definition of mirror pod OR static pod docs in FAQ wherever mirror pod is mentioned
2. add link to static pod docs wherever mirror pod is mentioned in the code
3. add a section around how CA treats mirror/static pods when draining a node

[Shubham82]

Hi @vadasambar, I didn't know about that about your PR that was closed
Thanks for mentioning it here.

add a section around how CA treats mirror/static pods when draining a node

In FAQ, there is mention about Mirror podes while scaling down the node, and its respective flags i.e. skip-nodes-with-system-pods and ignore-mirror-pods-utilization. i guess these flags explain what to do with mirror pods while draining a node.

https://github.com/kubernetes/autoscaler/blob/master/cluster-autoscaler/FAQ.md#how-does-scale-down-work

add link to official definition of mirror pod OR static pod docs in FAQ wherever mirror pod is mentioned

I will do that.

add link to static pod docs wherever mirror pod is mentioned in the code

I think not everywhere, which you mentioned in the comment here, I suggest mentioning it in the following place:
https://github.com/kubernetes/autoscaler/blob/master/cluster-autoscaler/utils/pod/pod.go#L45

[vadasambar]

In FAQ, there is mention about Mirror podes while scaling down the node

I guess you are talking about

The sum of cpu and memory requests of all pods running on this node (DaemonSet pods and Mirror pods are included by default but this is configurable with --ignore-daemonsets-utilization and --ignore-mirror-pods-utilization flags)

https://github.com/kubernetes/autoscaler/blob/master/cluster-autoscaler/FAQ.md#how-does-scale-down-work

As a user of CA(cluster-autoscaler), it is hard to understand how CA is going to treat mirror pods during (say) scale-down.

I think not everywhttps://github.com//pull/5565#discussion_r1133471107, which you mentioned in the comment here, I suggest mentioning it in the following place:

I think having it in all those places might be valuable because many of the places I mentioned don't refer to IsMirrorPod function directly. Open to other opinions here.

[Shubham82]

@vadasambar, If someone knows about Mirror Pods, before understanding the code. Mention everywhere I don't think it makes sense. but let's wait for other opinions.

[Shubham82]

cc @MaciekPytel