Allow adding extraVolumes in ClusterConfiguration for local etcd manifests

[frittentheke]

What keywords did you search in kubeadm issues before filing this one?

etcd, localEtcd, extraVolumes

Is this a BUG REPORT or FEATURE REQUEST?

FEATURE REQUEST

Versions

kubeadm version (use kubeadm version):

Environment:

• Kubernetes version (use kubectl version): kubeadm version: &version.Info{Major:"1", Minor:"13", GitVersion:"v1.13.4", GitCommit:"c27b913fddd1a6c480c229191a087698aa92f0b1", GitTreeState:"clean", BuildDate:"2019-02-28T13:35:32Z", GoVersion:"go1.11.5", Compiler:"gc", Platform:"linux/amd64"}
• Cloud provider or hardware configuration: AWS
• OS (e.g. from /etc/os-release): Container Linux
• Kernel (e.g. uname -a): 4.19
• Others: -

What happened?

I required to mount the hosts' /etc/hosts file to the etcd container / pod as the etcd peers are referenced by their names and those are updated automatically there.
With the etcd manifest file kubeadm init creates out of a provided ClusterConfiguration adding extraVolumes to the local etcd section throws a schema validation varning.

What you expected to happen?

Looking at the extraVolumes parameter that can be used for all other ControlPlaneComponents (https://godoc.org/k8s.io/kubernetes/cmd/kubeadm/app/apis/kubeadm#ControlPlaneComponent)
I expected the same to be possible to do so for etcd as well, but until now this is unfortunately not the case.

How to reproduce it (as minimally and precisely as possible)?

          apiVersion: "kubeadm.k8s.io/v1beta1"
          kind: ClusterConfiguration
          etcd:
            local:
              serverCertSANs:
                - "etcd-0"
              peerCertSANs:
                - "etcd-0"
              extraArgs:
                initial-cluster: etcd-0=https://etcd-0:2380
                initial-cluster-state: new
                name: etcd-0
                listen-peer-urls: https://0.0.0.0:2380
                listen-client-urls: https://0.0.0.0:2379
                advertise-client-urls: https://etcd-0:2379
                initial-advertise-peer-urls: https://etcd-0:2380
            extraVolumes:
                - name: hosts-file
                  hostPath: /etc/hosts
                  mountPath: /etc/hosts

[neolit123]

this seems like the first time someone requests this @frittentheke
we should probably discuss it at some point, thus i've added it to the Next milestone.

thanks

cc @kubernetes/sig-cluster-lifecycle

[timothysc]

We've decided against support of this feature, but it may be possible with future kustomize options in the future.