<p>I have updated my AKS Azure Kubernetes cluster to version 1.11.5, in this cluster a MongoDB Statefulset is running:</p>

<p>The statefulset is created with this file:</p>

<pre><code>---
apiVersion: rbac.authorization.k8s.io/v1beta1
kind: ClusterRoleBinding
metadata:
  name: default-view
roleRef:
  apiGroup: rbac.authorization.k8s.io
  kind: ClusterRole
  name: view
subjects:
  - kind: ServiceAccount
    name: default
    namespace: default
---
apiVersion: v1
kind: Service
metadata:
  name: mongo
  labels:
    name: mongo
spec:
  ports:
  - port: 27017
    targetPort: 27017
  clusterIP: None
  selector:
    role: mongo
---
apiVersion: apps/v1beta1
kind: StatefulSet
metadata:
  name: mongo
spec:
  serviceName: "mongo"
  replicas: 2
  template:
    metadata:
      labels:
        role: mongo
        environment: test
    spec:
      terminationGracePeriodSeconds: 10
      containers:
        - name: mongo
          image: mongo
          command:
            - mongod
            - "--replSet"
            - rs0
            - "--bind_ip"
            - 0.0.0.0            
            - "--smallfiles"
            - "--noprealloc"
          ports:
            - containerPort: 27017
          volumeMounts:
            - name: mongo-persistent-storage
              mountPath: /data/db
        - name: mongo-sidecar
          image: cvallance/mongo-k8s-sidecar
          env:
            - name: MONGO_SIDECAR_POD_LABELS
              value: "role=mongo,environment=test"
  volumeClaimTemplates:
  - metadata:
      name: mongo-persistent-storage
      annotations:
        volume.beta.kubernetes.io/storage-class: "managed-premium"
    spec:
      accessModes: [ "ReadWriteOnce" ]
      resources:
        requests:
          storage: 32Gi
</code></pre>

<p>after the mentioned update of the cluster to the new k8s version I get this error:</p>

<pre><code>mongo-0                        1/2     CrashLoopBackOff   6          9m
mongo-1                        2/2     Running            0          1h
</code></pre>

<p>the detailed log from the pod is the following:</p>

<pre><code>2018-12-18T14:28:44.281+0000 W STORAGE  [initandlisten] Detected configuration for non-active storage engine mmapv1 when current storage engine is wiredTiger
2018-12-18T14:28:44.281+0000 I CONTROL  [initandlisten]
2018-12-18T14:28:44.281+0000 I CONTROL  [initandlisten] ** WARNING: Access control is not enabled for the database.
2018-12-18T14:28:44.281+0000 I CONTROL  [initandlisten] **          Read and write access to data and configuration is unrestricted.
2018-12-18T14:28:44.281+0000 I CONTROL  [initandlisten] ** WARNING: You are running this process as the root user, which is not recommended.
2018-12-18T14:28:44.281+0000 I CONTROL  [initandlisten]
2018-12-18T14:28:44.281+0000 I CONTROL  [initandlisten]
2018-12-18T14:28:44.281+0000 I CONTROL  [initandlisten] ** WARNING: /sys/kernel/mm/transparent_hugepage/enabled is 'always'.
2018-12-18T14:28:44.281+0000 I CONTROL  [initandlisten] **        We suggest setting it to 'never'
2018-12-18T14:28:44.281+0000 I CONTROL  [initandlisten]
2018-12-18T14:28:44.477+0000 I FTDC     [initandlisten] Initializing full-time diagnostic data capture with directory '/data/db/diagnostic.data'
2018-12-18T14:28:44.478+0000 I REPL     [initandlisten] Rollback ID is 7
2018-12-18T14:28:44.479+0000 I REPL     [initandlisten] Recovering from stable timestamp: Timestamp(1545077719, 1) (top of oplog: { ts: Timestamp(1545077349, 1), t: 5 }, appliedThrough: { ts: Timestamp(1545077719, 1), t: 6 }, TruncateAfter: Timestamp(0, 0))
2018-12-18T14:28:44.480+0000 I REPL     [initandlisten] Starting recovery oplog application at the stable timestamp: Timestamp(1545077719, 1)
2018-12-18T14:28:44.480+0000 F REPL     [initandlisten] Applied op { : Timestamp(1545077719, 1) } not found. Top of oplog is { : Timestamp(1545077349, 1) }.
2018-12-18T14:28:44.480+0000 F -        [initandlisten] Fatal Assertion 40313 at src/mongo/db/repl/replication_recovery.cpp 361
2018-12-18T14:28:44.480+0000 F -        [initandlisten]

***aborting after fassert() failure
</code></pre>

<p>it seems the two instances went out of sync and are not able to recover. Can someone help?</p>

<p>I have workaround this issue:</p>

<ol>
<li>adding a MongoDB container to the cluster to dump and restore the MongoDB data</li>
<li>dumping the current database</li>
<li>deleting the MongoDB instance</li>
<li>recreating a new MongoDB instance</li>
<li>restoring the data to the new instance</li>
</ol>

<p>yes unfortunately this comes with  a downtime</p>
