<p>Consider the below PersistentVolumeClaim, as well as the Deployment using it.</p>

<p>Being ReadWriteOnce, the PVC can only be mounted by one node at the time. As there shall only be one replica of my deployment, I figured this should be fine. However, upon restarts/reloads, two Pods will co-exist during the switchover.</p>

<p>If Kubernetes decides to start the successor pod on the same node as the original pod, they will both be able to access the volume and the switchover goes fine. But - if it decides to start it on a new node, which it seems to prefer, my deployment ends up in a deadlock:</p>

<blockquote>
  <p>Multi-Attach error for volume "pvc-c474dfa2-9531-4168-8195-6d0a08f5df34" Volume is already used by pod(s) test-cache-5bb9b5d568-d9pmd</p>
</blockquote>

<p>The successor pod can't start because the volume is mounted on another node, while the original pod/node, of course, won't let go of the volume until the pod is taken out of service. Which it won't be until the successor is up.</p>

<p>What am I missing here?</p>

<hr>

<pre><code>apiVersion: v1
kind: PersistentVolumeClaim
metadata:
  name: vol-test
spec:
  accessModes:
  - ReadWriteOnce
  resources:
    requests:
      storage: 10Gi
  storageClassName: do-block-storage
---
apiVersion: apps/v1
kind: Deployment
metadata:
  name: test-cache
spec:
  selector:
    matchLabels:
      app: test-cache-deployment
  replicas: 1
  template:
    metadata:
      labels:
        app: test-cache-deployment
    spec:
      containers:
      - name: test-cache
        image: myrepo/test-cache:1.0-SNAPSHOT
        volumeMounts:
          - mountPath: "/test"
            name: vol-mount
        ports:
        - containerPort: 8080
        imagePullPolicy: Always
      volumes:
        - name: vol-mount
          persistentVolumeClaim:
            claimName: vol-name
      imagePullSecrets:
      - name: regcred
</code></pre>

John-Arne Boge
<p>I figured out a workaround:</p>

<p>While far from ideal, it's an acceptable compromise in my particular case.</p>

<p>ReadWriteOnce volumes apparently doesn't play well with Kubernetes default upgrade strategy: "Rolling" (even in the case of single replica deployments). If instead I use the "Recreate" upgrade strategy, Kubernetes will destroy the original pod before starting the successor, thus detaching the volume before it is mounted again.</p>

<pre><code>...
spec:
  selector:
    matchLabels:
      app: test-cache-deployment
  replicas: 1
  strategy:
    type: Recreate
...
</code></pre>

<p>This solution obviously comes with a major drawback: The deployment will be offline between shutdown and successful startup - which might take anywhere from a few seconds to eternity.</p>
