15. Kubernetes Operator

15. Kubernetes Operator#

        flowchart TB
    User[User] -->|create CR| API[API Server]
    API -->|watch| Controller[Operator Controller]
    Controller -->|reconcile| API
    API --> Deploy[Deployment]
    API --> Svc[Service]
    API --> CM[ConfigMap]
    API --> PVC[PVC]
    CRD[Custom Resource Definition] -->|register| API

Operator 模式#

Operator 通过定义**自定义资源(Custom Resource, CR)和控制器(Controller)**来扩展 Kubernetes 的能力。控制器持续监听自定义资源的变化，并通过协调(Reconcile)循环将实际状态调整为期望状态。

        flowchart LR
    A[Observe] --> B[Diff]
    B --> C[Act]
    C --> A
    style A fill:#9cf
    style B fill:#fc9
    style C fill:#9f9

自定义资源定义(CRD)#

apiVersion: apiextensions.k8s.io/v1
kind: CustomResourceDefinition
metadata:
  name: databases.example.com
spec:
  group: example.com
  versions:
    - name: v1
      served: true
      storage: true
      schema:
        openAPIV3Schema:
          type: object
          properties:
            spec:
              type: object
              properties:
                engine:
                  type: string
                  enum: ["mysql", "postgres"]
                version:
                  type: string
                replicas:
                  type: integer
                  minimum: 1
                  maximum: 5
                storage:
                  type: string
              required: ["engine", "version"]
            status:
              type: object
              properties:
                phase:
                  type: string
                ready:
                  type: boolean
      subresources:
        status: {}
      additionalPrinterColumns:
        - name: Engine
          type: string
          jsonPath: .spec.engine
        - name: Version
          type: string
          jsonPath: .spec.version
        - name: Ready
          type: boolean
          jsonPath: .status.ready
  scope: Namespaced
  names:
    plural: databases
    singular: database
    kind: Database
    shortNames:
      - db

自定义资源(CR)#

apiVersion: example.com/v1
kind: Database
metadata:
  name: my-mysql
spec:
  engine: mysql
  version: "8.0"
  replicas: 3
  storage: "50Gi"

# Use like any K8s resource
kubectl apply -f my-database.yaml
kubectl get databases
kubectl get db    # short name
kubectl describe db my-mysql
kubectl delete db my-mysql

Operator SDK#

# Install Operator SDK
brew install operator-sdk

# Scaffold a Go operator
operator-sdk init --domain example.com --repo github.com/myuser/db-operator
operator-sdk create api --group example --version v1 --kind Database --resource --controller

# Project structure
# ├── api/v1/database_types.go       # CR type definition
# ├── controllers/database_controller.go  # Reconciliation logic
# ├── config/                         # K8s manifests
# ├── Dockerfile
# ├── Makefile
# └── main.go

协调循环(Reconciliation Loop)简化示例#

func (r *DatabaseReconciler) Reconcile(ctx context.Context, req ctrl.Request) (ctrl.Result, error) {
    log := log.FromContext(ctx)

    // Fetch the Database CR
    var db examplev1.Database
    if err := r.Get(ctx, req.NamespacedName, &db); err != nil {
        return ctrl.Result{}, client.IgnoreNotFound(err)
    }

    // Create or update StatefulSet
    sts := &appsv1.StatefulSet{}
    err := r.Get(ctx, types.NamespacedName{Name: db.Name, Namespace: db.Namespace}, sts)
    if errors.IsNotFound(err) {
        sts = r.buildStatefulSet(&db)
        if err := r.Create(ctx, sts); err != nil {
            return ctrl.Result{}, err
        }
        log.Info("Created StatefulSet", "name", sts.Name)
    }

    // Update status
    db.Status.Ready = sts.Status.ReadyReplicas == *sts.Spec.Replicas
    db.Status.Phase = "Running"
    if err := r.Status().Update(ctx, &db); err != nil {
        return ctrl.Result{}, err
    }

    return ctrl.Result{RequeueAfter: 30 * time.Second}, nil
}

常用 Operator#

Operator

用途

安装方式

MySQL Operator

MySQL InnoDB 集群

helm install mysql-operator mysql/mysql-operator

CloudNativePG

PostgreSQL

helm install cnpg cloudnative-pg/cloudnative-pg

Redis Operator

Redis 集群

helm install redis-operator ot-helm/redis-operator

Prometheus Operator

监控体系

helm install kube-prometheus prometheus/kube-prometheus-stack

Strimzi

Apache Kafka

helm install strimzi strimzi/strimzi-kafka-operator

cert-manager

TLS 证书管理

helm install cert-manager jetstack/cert-manager

ECK

Elasticsearch

helm install eck elastic/eck-operator

Operator 生命周期管理器(OLM)#

# Install OLM
operator-sdk olm install

# Browse OperatorHub
# https://operatorhub.io

# Install an operator from OperatorHub
kubectl create -f https://operatorhub.io/install/prometheus.yaml
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