Can not access a MongoDB datastore with multiple instances.

Working with Data Drivers
1

I tried to deploy MongoDB deployment with Kubernetes, having three replicas which are accessing the same storage(PVC). Here is the configuration.

apiVersion: v1
kind: PersistentVolume
metadata:
  name: mongo-pv
spec:
  persistentVolumeReclaimPolicy: Retain
  capacity:
    storage: 1Gi
  accessModes:
  - ReadWriteOnce
  hostPath:
    path: "/data/mongo"
---
apiVersion: v1
kind: PersistentVolumeClaim
metadata:
  name: mongo-pvc
spec:
  accessModes:
  - ReadWriteOnce
  resources:
    requests:
      storage: 1Gi
---
apiVersion: apps/v1
kind: Deployment
metadata:
  creationTimestamp: null
  labels:
    app: mongo
  name: mongo
spec:
  replicas: 3
  selector:
    matchLabels:
      app: mongo
  template:
    metadata:
      labels:
        app: mongo
    spec:
      containers:
      - image: mongo
        name: mongo
        command: ["mongod"]
        args: ["--dbpath", "/data/db"]
        env:
        - name: MONGO_INITDB_ROOT_USERNAME
          value: root
        - name: MONGO_INITDB_ROOT_PASSWORD
          value: pwd
        volumeMounts:
        - name: mongo-data-dir
          mountPath: /data/db
      volumes:
      - name: mongo-data-dir
        persistentVolumeClaim:
          claimName: mongo-pvc
---
apiVersion: v1
kind: Service
metadata:
  labels:
    app: mongo
  name: mongo-nodeport-svc
spec:
  ports:
  - port: 27017
    protocol: TCP
    targetPort: 27017
    nodePort: 32000
  selector:
    app: mongo
  type: NodePort

When you apply this configuration file kubectl apply -f file_name.yaml , you can create three pods, which are accessing the same storage for the databases. When you check the pods’ status kubectl get pods , you can see only one pod becomes running and others be in a CrashLoop state. What is happening is, when creating more than one instance to use a common storage, only one instance can acquire the lock of the mongod.loc (Unable to lock the lock file: /data/db/mongod.loc)

What’s why only one pod becomes healthy and others in CrashLoopBackOff.( you can see this using kubectl logs pod-name). What I want is,

  1. Can I release the lock of the mongod.loc file and use the storage for all the pods?(this mostly can not, because of consistency issues)
  2. If not, how can I create the proposed idea?( accessing a single storage/volume using multiple pod instances)?
  3. Would you suggest other ideas to achieve accessing a single storage using multiple pod instances?

Your answers and help are welcomed.

2

Hi,

This isn’t something we’d recommend trying to do - it undermines the benefit of having multiple members in the replica set in the first place by having a single point of failure at the storage level if the disk fails.

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