feature request: "currentState.replicas" count in replicationController API

[sym3tri]

Similar to how the current desiredState section specifies the number of replicas, it would be useful to show how many pods are currently satisfying that desired state. ie:

"desiredState": {
  "replicas": 3,
  ...
},
"currentState": {
  "replicas": 2
}

Effectively this would provide a "status" for the RC.
The only way (I am aware of) to do this now is by getting the RC's selector query, polling the pod list with that label query, and counting the results.

[kelseyhightower]

I would love to work on this one.

[kelseyhightower]

@brendanburns @smarterclayton Thoughts on adding support for this? I would like to hack on it if people thinks it's a good idea.

[lavalamp]

@kelseyhightower go for it. The only way to implement it right now is to have the replicationController storage object (in pkg/registry), when it gets a GET request for a rep. Controller, list the pods matching the label selector, count the result, and place that in current state. Currently it'll be extremely inefficient, but we can fix that when we have some concept of indexes or something.

[brendandburns]

+1 Go for it!

We can add a caching layer for pod listing (I've been thinking this is a good idea anyway), which can watch the pod list, and update the cache dynamically.

[brendandburns]

Is this underway? If there's no work on it, I'll work on getting it done.

[lavalamp]

Before doing this consider that a naive implementation will currently make listing rep. controllers an O(rep controller count * pod count operation).

[brendandburns]

Done in #1248