Kubernetes yaml deployment - unable to create a symbolic link-CodePudding

I am trying to make an nginx deployment and during the container creation, I want to create multiply symbolic links. But for some reason, it doesn't work and the container crashes.

apiVersion: apps/v1
kind: Deployment
metadata:
  labels:
    app: tcc
    component: nginx
  name: tcc-nginx-deployment
  namespace: dev2
spec:
  replicas: 1
  selector:
    matchLabels:
      app: tcc
      component: nginx
  template:
    metadata:
      labels:
        app: tcc
        component: nginx
    spec:
      containers:
      - image: nginx
        name: nginx
        command:
              - /bin/sh
              - -c
              - |
                ln -s /shared/apps/ /var/www
                rm -r /etc/nginx/conf.d
                ln -s /shared/nginx-config/ /etc/nginx/conf.d

        ports:
        - containerPort: 80
          protocol: TCP
        volumeMounts:
        - mountPath: /shared
          name: efs-pvc
      volumes:
      - name: efs-pvc
        persistentVolumeClaim:
          claimName: tcc-efs-storage-claim

CodePudding user response：

That's because you are asking container just to create symbolic links. So once those
symbolic links are created container is getting exited.
To avoid that add "nginx" "-g" "daemon off;" as following:

apiVersion: apps/v1
kind: Deployment
metadata:
  labels:
    app: tcc
    component: nginx
  name: tcc-nginx-deployment
spec:
  replicas: 1
  selector:
    matchLabels:
      app: tcc
      component: nginx
  template:
    metadata:
      labels:
        app: tcc
        component: nginx
    spec:
      containers:
      - image: nginx
        name: nginx
        imagePullPolicy: IfNotPresent
        command:
              - /bin/sh
              - -c
              - |
                ln -s /shared/apps/ /var/www
                rm -r /etc/nginx/conf.d
                ln -s /shared/nginx-config/ /etc/nginx/conf.d
                "nginx" "-g" "daemon off;" ; # after creating above symbolic links it will start nginx daemon 
        ports:
        - containerPort: 80
          protocol: TCP
        volumeMounts:
        - mountPath: /shared
          name: efs-pvc
      volumes:
      - name: efs-pvc
        persistentVolumeClaim:
          claimName: tcc-efs-storage-claim

CodePudding user response：

The container is not running, because after the command block is executed, container is exiting, which is expected behaviour.

Instead of playing with symbolic links in command in yaml template (which is not the best practice solution), why just don't use solution builtin Kubernetes and do not use command block at all?

You should use subPath which is designed to share directories from one volume for multiple, different directories on the single pod:

Sometimes, it is useful to share one volume for multiple uses in a single pod. The volumeMounts.subPath property specifies a sub-path inside the referenced volume instead of its root.

In your case, the deployment yaml should look like this:

apiVersion: apps/v1
kind: Deployment
metadata:
  labels:
    app: tcc
    component: nginx
  name: tcc-nginx-deployment
  namespace: dev2
spec:
  replicas: 1
  selector:
    matchLabels:
      app: tcc
      component: nginx
  template:
    metadata:
      labels:
        app: tcc
        component: nginx
    spec:
      containers:
      - image: nginx
        name: nginx
        ports:
        - containerPort: 80
          protocol: TCP
        volumeMounts:
        - mountPath: /shared
          name: efs-pvc
        - mountPath: /etc/nginx/conf.d
          name: efs-pvc
          subPath: nginx-config
        - mountPath: /var/www
          name: efs-pvc
          subPath: apps
      volumes:
      - name: efs-pvc
        persistentVolumeClaim:
          claimName: tcc-efs-storage-claim

Also if you want to mount only config files for NGINX, you may use ConfigMap instead of volume - check this answer for more information.