Adds featureGates to already templated services

[asiegman]

what

• Allows kops to configure feature gates on the kubernetes API server, kubelet, and kube-proxy
• Will look for KOPS_KUBE_API_SERVER_FEATURE_GATES as a comma separated list of key=value pairs for kube api server
• kubelet looks for KOPS_KUBE_KUBELET_FEATURE_GATES
• kubeproxy looks for KOPS_KUBE_PROXY_FEATURE_GATES

Of note, I did not add support for scheduler or controller manager since you're currently not deviating from defaults there. I could add those if you'd like.

Also of note: I don't do error checking on input formatting here, as I felt it would overly complicate the template. I'm also not sure the best way to do that, so there's also that. Things will fail if the environment variables are not set as feature1="false",feature2="true" and so on.

why

• to enable/disable alpha and beta features

example parsing

$ gomplate -f /localhost/work/cloudposse/reference-architectures/templates/kops/kops-private-topology.yaml.gotmpl | grep -C5 feature
# no output, note added for clarity
$ export KOPS_KUBE_API_SERVER_FEATURE_GATES="ExpandInUsePersistentVolumes=true,SomeOtherFeature=false"
$ gomplate -f /localhost/work/cloudposse/reference-architectures/templates/kops/kops-private-topology.yaml.gotmpl | grep -C5 feature
      type: Public
      idleTimeoutSeconds: 600
  kubeAPIServer:
    anonymousAuth: false
    authorizationMode: RBAC
    featureGates:
      ExpandInUsePersistentVolumes: true
      SomeOtherFeature: false
    admissionControl:
    - NamespaceLifecycle
    - LimitRanger

references

• https://kubernetes.io/docs/reference/command-line-tools-reference/feature-gates/#feature-gates-for-alpha-or-beta-features
• https://github.com/kubernetes/kops/blob/master/docs/cluster_spec.md#feature-gates

[asiegman]

Refactored the variables I use and how they are applied. Now a single variable. Will make it easier if we want to add the other sections feature gates can apply to.

[maximmi]

@Nuru could you please check and approve?

[osterman]

We're going to deprecate this version of the reference architecture in favor of a simpler one.