Service Account

Service account 是为了方便 Pod 里面的进程调用 Kubernetes API 或其他外部服务而设计的。它与 User account 不同

• User account 是为人设计的，而 service account 则是为 Pod 中的进程调用 Kubernetes API 而设计；
• User account 是跨 namespace 的，而 service account 则是仅局限它所在的 namespace；
• 每个 namespace 都会自动创建一个 default service account
• Token controller 检测 service account 的创建，并为它们创建 secret
• 开启 ServiceAccount Admission Controller 后
  • 每个 Pod 在创建后都会自动设置 spec.serviceAccountName 为 default（除非指定了其他 ServiceAccout）
  • 验证 Pod 引用的 service account 已经存在，否则拒绝创建
  • 如果 Pod 没有指定 ImagePullSecrets，则把 service account 的 ImagePullSecrets 加到 Pod 中
  • 每个 container 启动后都会挂载该 service account 的 token 和 ca.crt 到 /var/run/secrets/kubernetes.io/serviceaccount/

$ kubectl exec nginx-3137573019-md1u2 ls /var/run/secrets/kubernetes.io/serviceaccount
ca.crt
namespace
token

注：你可以使用 https://jwt.io/ 来查看 token 的详细信息（如 PAYLOAD、SIGNATURE 等）。

创建 Service Account

$ kubectl create serviceaccount jenkins
serviceaccount "jenkins" created
$ kubectl get serviceaccounts jenkins -o yaml
apiVersion: v1
kind: ServiceAccount
metadata:
  creationTimestamp: 2017-05-27T14:32:25Z
  name: jenkins
  namespace: default
  resourceVersion: "45559"
  selfLink: /api/v1/namespaces/default/serviceaccounts/jenkins
  uid: 4d66eb4c-42e9-11e7-9860-ee7d8982865f
secrets:
- name: jenkins-token-l9v7v

自动创建的 secret：

kubectl get secret jenkins-token-l9v7v -o yaml
apiVersion: v1
data:
  ca.crt: (APISERVER CA BASE64 ENCODED)
  namespace: ZGVmYXVsdA==
  token: (BEARER TOKEN BASE64 ENCODED)
kind: Secret
metadata:
  annotations:
    kubernetes.io/service-account.name: jenkins
    kubernetes.io/service-account.uid: 4d66eb4c-42e9-11e7-9860-ee7d8982865f
  creationTimestamp: 2017-05-27T14:32:25Z
  name: jenkins-token-l9v7v
  namespace: default
  resourceVersion: "45558"
  selfLink: /api/v1/namespaces/default/secrets/jenkins-token-l9v7v
  uid: 4d697992-42e9-11e7-9860-ee7d8982865f
type: kubernetes.io/service-account-token

添加 ImagePullSecrets

apiVersion: v1
kind: ServiceAccount
metadata:
  creationTimestamp: 2015-08-07T22:02:39Z
  name: default
  namespace: default
  selfLink: /api/v1/namespaces/default/serviceaccounts/default
  uid: 052fb0f4-3d50-11e5-b066-42010af0d7b6
secrets:
- name: default-token-uudge
imagePullSecrets:
- name: myregistrykey

授权

Service Account 为服务提供了一种方便的认证机制，但它不关心授权的问题。可以配合 RBAC 来为 Service Account 鉴权：

• 配置 --authorization-mode=RBAC 和 --runtime-config=rbac.authorization.k8s.io/v1alpha1
• 配置 --authorization-rbac-super-user=admin
• 定义 Role、ClusterRole、RoleBinding 或 ClusterRoleBinding

比如

# This role allows to read pods in the namespace "default"
kind: Role
apiVersion: rbac.authorization.k8s.io/v1alpha1
metadata:
  namespace: default
  name: pod-reader
rules:
  - apiGroups: [""] # The API group"" indicates the core API Group.
    resources: ["pods"]
    verbs: ["get", "watch", "list"]
    nonResourceURLs: []
---
# This role binding allows "default" to read pods in the namespace "default"
kind: RoleBinding
apiVersion: rbac.authorization.k8s.io/v1alpha1
metadata:
  name: read-pods
  namespace: default
subjects:
  - kind: ServiceAccount # May be "User", "Group" or "ServiceAccount"
    name: default
roleRef:
  kind: Role
  name: pod-reader
  apiGroup: rbac.authorization.k8s.io