# PodPreset

PodPreset 用来给指定标签的 Pod 注入额外的信息，如环境变量、存储卷等。这样，Pod 模板就不需要为每个 Pod 都显式设置重复的信息。

当然，你也可以给 Pod 增加注解 `podpreset.admission.kubernetes.io/exclude: "true"` 来避免它们被 PodPreset 修改。

## API 版本对照表

| Kubernetes 版本 | API 版本                   | 默认开启 |
| ------------- | ------------------------ | ---- |
| v1.6+         | settings.k8s.io/v1alpha1 | 否    |

### 开启 PodPreset

* 开启 API `kube-apiserver --runtime-config=settings.k8s.io/v1alpha1=true`
* 开启准入控制 `--enable-admission-plugins=..,PodPreset`

## PodPreset 示例

增加环境变量和存储卷的 PodPreset

```yaml
kind: PodPreset
apiVersion: settings.k8s.io/v1alpha1
metadata:
  name: allow-database
  namespace: myns
spec:
  selector:
    matchLabels:
      role: frontend
  env:
    - name: DB_PORT
      value: "6379"
  volumeMounts:
    - mountPath: /cache
      name: cache-volume
  volumes:
    - name: cache-volume
      emptyDir: {}
```

用户提交 Pod

```yaml
apiVersion: v1
kind: Pod
metadata:
  name: website
  labels:
    app: website
    role: frontend
spec:
  containers:
    - name: website
      image: ecorp/website
      ports:
        - containerPort: 80
```

经过准入控制 `PodPreset` 后，Pod 会自动增加环境变量和存储卷

```yaml
apiVersion: v1
kind: Pod
metadata:
  name: website
  labels:
    app: website
    role: frontend
  annotations:
    podpreset.admission.kubernetes.io/allow-database: "resource version"
spec:
  containers:
    - name: website
      image: ecorp/website
      volumeMounts:
        - mountPath: /cache
          name: cache-volume
      ports:
        - containerPort: 80
      env:
        - name: DB_PORT
          value: "6379"
  volumes:
    - name: cache-volume
      emptyDir: {}
```

## ConfigMap 示例

ConfigMap

```yaml
apiVersion: v1
kind: ConfigMap
metadata:
  name: etcd-env-config
data:
  number_of_members: "1"
  initial_cluster_state: new
  initial_cluster_token: DUMMY_ETCD_INITIAL_CLUSTER_TOKEN
  discovery_token: DUMMY_ETCD_DISCOVERY_TOKEN
  discovery_url: http://etcd_discovery:2379
  etcdctl_peers: http://etcd:2379
  duplicate_key: FROM_CONFIG_MAP
  REPLACE_ME: "a value"
```

PodPreset

```yaml
kind: PodPreset
apiVersion: settings.k8s.io/v1alpha1
metadata:
  name: allow-database
  namespace: myns
spec:
  selector:
    matchLabels:
      role: frontend
  env:
    - name: DB_PORT
      value: 6379
    - name: duplicate_key
      value: FROM_ENV
    - name: expansion
      value: $(REPLACE_ME)
  envFrom:
    - configMapRef:
        name: etcd-env-config
  volumeMounts:
    - mountPath: /cache
      name: cache-volume
    - mountPath: /etc/app/config.json
      readOnly: true
      name: secret-volume
  volumes:
    - name: cache-volume
      emptyDir: {}
    - name: secret-volume
      secretName: config-details
```

用户提交的 Pod

```yaml
apiVersion: v1
kind: Pod
metadata:
  name: website
  labels:
    app: website
    role: frontend
spec:
  containers:
    - name: website
      image: ecorp/website
      ports:
        - containerPort: 80
```

经过准入控制 `PodPreset` 后，Pod 会自动增加 ConfigMap 环境变量

```yaml
apiVersion: v1
kind: Pod
metadata:
  name: website
  labels:
    app: website
    role: frontend
  annotations:
    podpreset.admission.kubernetes.io/allow-database: "resource version"
spec:
  containers:
    - name: website
      image: ecorp/website
      volumeMounts:
        - mountPath: /cache
          name: cache-volume
        - mountPath: /etc/app/config.json
          readOnly: true
          name: secret-volume
      ports:
        - containerPort: 80
      env:
        - name: DB_PORT
          value: "6379"
        - name: duplicate_key
          value: FROM_ENV
        - name: expansion
          value: $(REPLACE_ME)
      envFrom:
        - configMapRef:
          name: etcd-env-config
  volumes:
    - name: cache-volume
      emptyDir: {}
    - name: secret-volume
      secretName: config-details
```

## 修改 Pod 时区示例

下面的示例会把带有标签 `tz: shanghai`的所有Pod都自动改成上海时区：

```yaml
kind: PodPreset
apiVersion: settings.k8s.io/v1alpha1
metadata:
  name: tz-shanghai
  namespace: default
spec:
  selector:
    matchLabels:
      tz: shanghai
  volumeMounts:
    - mountPath: /etc/localtime
      name: tz-config
  volumes:
    - name: tz-config
      hostPath:
        path: /usr/share/zoneinfo/Asia/Shanghai
```


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