StatefulSet を使ってみる (kubernetes)

kubernetes

Published: 2020-12-31

やったこと

StatefulSet を使ってみます。

確認環境

$ k version
Client Version: version.Info{Major:"1", Minor:"16", GitVersion:"v1.16.2", GitCommit:"c97fe5036ef3df2967d086711e6c0c405941e14b", GitTreeState:"clean", BuildDate:"2019-10-15T19:18:23Z", GoVersion:"go1.12.10", Compiler:"gc", Platform:"darwin/amd64"}
Server Version: version.Info{Major:"1", Minor:"19", GitVersion:"v1.19.3", GitCommit:"1e11e4a2108024935ecfcb2912226cedeafd99df", GitTreeState:"clean", BuildDate:"2020-10-14T12:41:49Z", GoVersion:"go1.15.2", Compiler:"gc", Platform:"linux/amd64"}

調査

StatefulSetは下記の1つ以上の項目を要求するアプリケーションにおいて最適です。

安定した一意のネットワーク識別子

安定した永続ストレージ

規則的で安全なデプロイとスケーリング

規則的で自動化されたローリングアップデート

first-stateful.yaml

apiVersion: apps/v1
kind: StatefulSet
metadata:
  name: my-statefulset
spec:
  serviceName: nginx
  replicas: 2 # by default is 1
  selector:
    matchLabels:
      app: nginx
  template:
    metadata:
      labels:
        app: nginx # .spec.selector.matchLabelsの値と一致する必要があります
    spec:
      terminationGracePeriodSeconds: 10
      containers:
      - name: nginx-container
        image: nginx:1.17
        ports:
        - containerPort: 80
          name: web
        volumeMounts:
        - name: www
          mountPath: /usr/share/nginx/html
  volumeClaimTemplates:
  - metadata:
      name: www
    spec:
      accessModes:
      - ReadWriteOnce
      storageClassName: "my-storage-class"
      resources:
        requests:
          storage: 1Gi

$ k apply -f first-stateful.yaml
statefulset.apps/my-statefulset created

$ k get statefulsets
NAME             READY   AGE
my-statefulset   2/2     12m

$ k get pods -o wide
NAME               READY   STATUS    RESTARTS   AGE   IP           NODE             NOMINATED NODE   READINESS GATES
my-statefulset-0   1/1     Running   0          11m   10.1.0.180   docker-desktop   <none>           <none>
my-statefulset-1   1/1     Running   0          11m   10.1.0.181   docker-desktop   <none>           <none>

$ k get pv
NAME                                       CAPACITY   ACCESS MODES   RECLAIM POLICY   STATUS   CLAIM                          STORAGECLASS   REASON   AGE
pvc-0ec2bcbb-1a20-46b0-8930-5fe48601a180   1Gi        RWO            Delete           Bound    default/www-my-statefulset-1   hostpath                12m
pvc-dc6cf56f-2e32-4d53-ad5e-9fa0fd9bc365   1Gi        RWO            Delete           Bound    default/www-my-statefulset-0   hostpath                12m

$ k get pvc
NAME                   STATUS   VOLUME                                     CAPACITY   ACCESS MODES   STORAGECLASS   AGE
www-my-statefulset-0   Bound    pvc-dc6cf56f-2e32-4d53-ad5e-9fa0fd9bc365   1Gi        RWO            hostpath       12m
www-my-statefulset-1   Bound    pvc-0ec2bcbb-1a20-46b0-8930-5fe48601a180   1Gi        RWO            hostpath       12m

永続ボリュームの動作を確認

# ファイルを設置する
$ k exec -it my-statefulset-0 -- ls /usr/share/nginx/html
$ k exec -it my-statefulset-0 -- touch /usr/share/nginx/html/hoge
$ k exec -it my-statefulset-0 -- ls /usr/share/nginx/html
hoge

# Pod を削除する
$ k delete pod my-statefulset-0
pod "my-statefulset-0" deleted

$ k get pods
NAME               READY   STATUS    RESTARTS   AGE
my-statefulset-0   1/1     Running   0          47s
my-statefulset-1   1/1     Running   0          16m

# my-statefulset-0 でファイルがあることを確認する
$ k exec -it my-statefulset-0 -- ls /usr/share/nginx/html
hoge

参考

StatefulSet | Kubernetes