Map horizontal-pod-autoscaler-use-rest-clients flag

[itskingori]

Maps --horizontal-pod-autoscaler-use-rest-clients flag which is required for Horizontal Pod Autoscaling. See Kubernetes code in kubernetes/kubernetes/blob/v1.7.11/cmd/kube-controller-manager/app/autoscaling.go#L36-L39.

Seems this is the missing piece for fulfilment of HPA pre-requisites, which are:

• ✅ Enable the Aggregation Layer via the following kube-apiserver flags
  • ✅ --requestheader-client-ca-file=<path to aggregator CA cert> (see Initial aggregation work #3679)
  • ✅ --requestheader-allowed-names=aggregator (see Initial aggregation work #3679)
  • ✅ --requestheader-extra-headers-prefix=X-Remote-Extra- (see Initial aggregation work #3679)
  • ✅ --requestheader-group-headers=X-Remote-Group (see Initial aggregation work #3679)
  • ✅ --requestheader-username-headers=X-Remote-User (see Initial aggregation work #3679)
  • ✅ --proxy-client-cert-file=<path to aggregator proxy cert> (see Add proxy client support #3165)
  • ✅ --proxy-client-key-file=<path to aggregator proxy key> (see Add proxy client support #3165)
• ❓ Horizontal Pod Scaling ... set the appropriate flags for kube-controller-manager:
  • ❎ --horizontal-pod-autoscaler-use-rest-clients should be true.
  • ✅ --kubeconfig <path-to-kubeconfig> (already set)

Relevant Documentation:

• https://v1-7.docs.kubernetes.io/docs/tasks/run-application/horizontal-pod-autoscale/
• https://v1-7.docs.kubernetes.io/docs/tasks/access-kubernetes-api/configure-aggregation-layer/

Relevant Issues & PRs:

• Initial aggregation work #3679
• Support Aggregation Layer #3152
• Proposal: APIServer fields for authenticating proxy #2691
• Custom metrics support #2652
• Add proxy client support #3165

[mikesplain]

@itskingori I believe you also need to run make apimachinery and checkin the results. See https://github.com/kubernetes/kops/blob/236cb0f188227e34dc09e246ef2f4c5682d64e39/docs/development/api_updates.md

/ok-to-test

[itskingori]

I believe you also need to run make apimachinery and checkin the results.

@mikesplain done in 28ff1bf.

[mikesplain]

/lgtm

Though, you'll have to wait for someone else to take a look as well. Thanks!

[itskingori]

@chrislovecnm @justinsb wondering if this should default to true if EnableCustomMetrics is true 🤔

[chrislovecnm]

Can we get all of that awesome stuff in the comments into documentation?

[justinsb]

/lgtm

I want to get the flag into beta2 (which I'm about to cut).

Honestly I don't know if we should default this to true if EnableCustomMetrics is true - I'm guessing yes, at least in 1.8 or 1.9. Is there someone we can ask?

[k8s-ci-robot]

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[k8s-github-robot]

/test all [submit-queue is verifying that this PR is safe to merge]

[k8s-github-robot]

Automatic merge from submit-queue.

[itskingori]

Honestly I don't know if we should default this to true if EnableCustomMetrics is true - I'm guessing yes, at least in 1.8 or 1.9. Is there someone we can ask?

@justinsb Maybe we could leave it off for now.

Can we get all of that awesome stuff in the comments into documentation?

@chrislovecnm I'll write something up for HPA ... currently trying to set it up in my cluster.