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kubeadmでEpehemeral Containerを有効にする

8 min read

kubernetes 1.22で kubectl debug コマンドを有効にするには --feature-gates で有効化をする必要があります.

k8s1% kubectl debug sample-pod --image=amsy810/tools:v2.0 -it -- bash
Defaulting debug container name to debugger-lc6mh.
error: ephemeral containers are disabled for this cluster (error from server: "the server could not find the requested resource").

環境は次の通り.

% kubeadm config images list
k8s.gcr.io/kube-apiserver:v1.22.1
k8s.gcr.io/kube-controller-manager:v1.22.1
k8s.gcr.io/kube-scheduler:v1.22.1
k8s.gcr.io/kube-proxy:v1.22.1
k8s.gcr.io/pause:3.5
k8s.gcr.io/etcd:3.5.0-0
k8s.gcr.io/coredns/coredns:v1.8.4

TL;DR

コンポーネントのConfigで --feature-gates=EphemeralContainers=true をControl plane, worker nodeの 全ノードで有効化 する必要があります.

Control plane

% sudo vim /var/lib/kubelet/kubeadm-flags.env
KUBELET_KUBEADM_ARGS="--container-runtime=remote --container-runtime-endpoint=/run/containerd/containerd.sock --pod-infra-container-image=k8s.gcr.io/pause:3.4.1 --feature-gates=EphemeralContainers=true"
% sudo vim  /etc/kubernetes/manifests/kube-apiserver.yaml
apiVersion: v1
kind: Pod
...
    - --etcd-servers=https://127.0.0.1:2379
    - --feature-gates=EphemeralContainers=true
    - --insecure-port=0
...
% sudo vim /etc/kubernetes/manifests/kube-scheduler.yaml
apiVersion: v1
kind: Pod
...
    - --bind-address=127.0.0.1
    - --feature-gates=EphemeralContainers=true
    - --kubeconfig=/etc/kubernetes/scheduler.conf
% sudo systemctl daemon-reload
% sudo systemctl restart kubelet

Worker nodes

% sudo vim /var/lib/kubelet/kubeadm-flags.env
KUBELET_KUBEADM_ARGS="--container-runtime=remote --container-runtime-endpoint=/run/containerd/containerd.sock --pod-infra-container-image=k8s.gcr.io/pause:3.4.1 --feature-gates=EphemeralContainers=true"
% sudo systemctl daemon-reload
% sudo systemctl restart kubelet

Ephemeral ContainerはAlpha

v1.22時点ではデフォルト無効化されており,明示的に有効化が必要です.

https://kubernetes.io/docs/reference/command-line-tools-reference/feature-gates/
Feature	                Default	Stage	Since	Until
EphemeralContainers	false	Alpha	1.16	

kubeadmの設定

how to enable resource EphemeralContainers in Rancher kubernetes
で設定例がありました.

最初はControl planeのコンポーネントだけに設定していましたが,worker nodesで動くkubeletコンポーネントにも設定することを忘れていました.

Control plane

% sudo vim /var/lib/kubelet/kubeadm-flags.env
KUBELET_KUBEADM_ARGS="--container-runtime=remote --container-runtime-endpoint=/run/containerd/containerd.sock --pod-infra-container-image=k8s.gcr.io/pause:3.4.1 --feature-gates=EphemeralContainers=true"
% sudo vim  /etc/kubernetes/manifests/kube-apiserver.yaml
apiVersion: v1
kind: Pod
...
    - --etcd-servers=https://127.0.0.1:2379
    - --feature-gates=EphemeralContainers=true
    - --insecure-port=0
...
% sudo vim /etc/kubernetes/manifests/kube-scheduler.yaml
apiVersion: v1
kind: Pod
...
    - --bind-address=127.0.0.1
    - --feature-gates=EphemeralContainers=true
    - --kubeconfig=/etc/kubernetes/scheduler.conf

Worker nodes

% sudo vim /var/lib/kubelet/kubeadm-flags.env
KUBELET_KUBEADM_ARGS="--container-runtime=remote --container-runtime-endpoint=/run/containerd/containerd.sock --pod-infra-container-image=k8s.gcr.io/pause:3.4.1 --feature-gates=EphemeralContainers=true"
% sudo systemctl daemon-reload
% sudo systemctl restart kubelet

kubectl debug

Debug Running Pods に従って試すと,シェルが取れるようになっています.

k8s1% kubectl run ephemeral-demo --image=k8s.gcr.io/pause:3.1 --restart=Never
pod/ephemeral-demo created
k8s1% kubectl exec -it ephemeral-demo -- sh
error: Internal error occurred: error executing command in container: failed to exec in container: failed to start exec "b3495e0398f0597e479e534be958ed8f254afc0e45052162cfb13847b3bee79a": OCI runtime exec failed: exec failed: container_linux.go:380: starting container process caused: exec: "sh": executable file not found in $PATH: unknown
k8s1% kubectl debug -it ephemeral-demo --image=busybox --target=ephemeral-demo
Targeting container "ephemeral-demo". If you don't see processes from this container it may be because the container runtime doesn't support this feature.
Defaulting debug container name to debugger-pgvbp.
If you don't see a command prompt, try pressing enter.
/ # hostname
ephemeral-demo

Epehmeral Containerが起動していることがわかります.

k8s1% k describe po ephemeral-demo
Name:         ephemeral-demo
Namespace:    default
Priority:     0
Node:         k8s3/192.168.5.112
Start Time:   Mon, 30 Aug 2021 22:01:23 +0900
Labels:       run=ephemeral-demo
Annotations:  cni.projectcalico.org/podIP: 10.244.219.11/32
              cni.projectcalico.org/podIPs: 10.244.219.11/32
Status:       Running
IP:           10.244.219.11
IPs:
  IP:  10.244.219.11
Containers:
  ephemeral-demo:
    Container ID:   containerd://1710d670716c4c480168cf1d76a6554739e591a00a99eed5f91fd783a8f526c7
    Image:          k8s.gcr.io/pause:3.1
    Image ID:       k8s.gcr.io/pause@sha256:f78411e19d84a252e53bff71a4407a5686c46983a2c2eeed83929b888179acea
    Port:           <none>
    Host Port:      <none>
    State:          Running
      Started:      Mon, 30 Aug 2021 22:01:23 +0900
    Ready:          True
    Restart Count:  0
    Environment:    <none>
    Mounts:
      /var/run/secrets/kubernetes.io/serviceaccount from kube-api-access-nv77s (ro)
Ephemeral Containers:
  debugger-pgvbp:
    Container ID:   containerd://ca669ac90de7852367c1977eef322d5388778e9d95db5a4c71d39f82523aa981
    Image:          busybox
    Image ID:       docker.io/library/busybox@sha256:b37dd066f59a4961024cf4bed74cae5e68ac26b48807292bd12198afa3ecb778
    Port:           <none>
    Host Port:      <none>
    State:          Terminated
      Reason:       Completed
      Exit Code:    0
      Started:      Mon, 30 Aug 2021 22:01:37 +0900
      Finished:     Mon, 30 Aug 2021 22:02:34 +0900
    Ready:          False
    Restart Count:  0
    Environment:    <none>
    Mounts:         <none>
Conditions:
  Type              Status
  Initialized       True
  Ready             True
  ContainersReady   True
  PodScheduled      True
Volumes:
  kube-api-access-nv77s:
    Type:                    Projected (a volume that contains injected data from multiple sources)
    TokenExpirationSeconds:  3607
    ConfigMapName:           kube-root-ca.crt
    ConfigMapOptional:       <nil>
    DownwardAPI:             true
QoS Class:                   BestEffort
Node-Selectors:              <none>
Tolerations:                 node.kubernetes.io/not-ready:NoExecute op=Exists for 300s
                             node.kubernetes.io/unreachable:NoExecute op=Exists for 300s
Events:
  Type    Reason     Age   From               Message
  ----    ------     ----  ----               -------
  Normal  Scheduled  83s   default-scheduler  Successfully assigned default/ephemeral-demo to k8s3
  Normal  Pulled     83s   kubelet            Container image "k8s.gcr.io/pause:3.1" already present on machine
  Normal  Created    83s   kubelet            Created container ephemeral-demo
  Normal  Started    83s   kubelet            Started container ephemeral-demo
  Normal  Pulling    71s   kubelet            Pulling image "busybox"
  Normal  Pulled     69s   kubelet            Successfully pulled image "busybox" in 1.755345903s
  Normal  Created    69s   kubelet            Created container debugger-pgvbp
  Normal  Started    69s   kubelet            Started container debugger-pgvbp

ref

https://github.com/kubernetes/kubernetes/blob/master/CHANGELOG/CHANGELOG-1.20.md#kubectl-debug-graduates-to-beta

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