在使用service之前，首先利用deployment创建出3个pod，注意要为pod设置app=nginx-pod的标签
创建deployment.yaml，内容如下
apiVersion: apps/v1 kind: Deployment metadata: name: pc-deployment namespace: dev spec: replicas: 3 selector: matchLabels: app: nginx-pod template: metadata: labels: app: nginx-pod spec: containers: - name: nginx image: nginx:1.17.1 ports: - containerPort: 80