My Kubernetes MongoDB service isn't persisting the data

Question

This is the mongodb yaml file.

apiVersion: apps/v1
kind: Deployment
metadata:
  name: auth-mongo-depl
spec:
  replicas: 1
  selector:
    matchLabels:
      app: auth-mongo
  template:
    metadata:
      labels:
        app: auth-mongo
    spec:
      containers:
        - name: auth-mongo
          image: mongo
          volumeMounts:
            - mountPath: "/data/db/auth"
              name: auth-db-storage
      volumes:
        - name: auth-db-storage
          persistentVolumeClaim:
            claimName: mongo-pvc
---
apiVersion: v1
kind: Service
metadata:
  name: auth-mongo-srv
spec:
  selector:
    app: auth-mongo
  ports:
    - name: db
      protocol: TCP
      port: 27017
      targetPort: 27017

And this is the persistent volume file.

apiVersion: v1
kind: PersistentVolume
metadata:
  name: mongo-pv
  labels:
    type: local
spec:
  storageClassName: mongo
  capacity:
    storage: 5Gi
  accessModes:
    - ReadWriteOnce
  hostPath:
    path: "/data/db"
---
apiVersion: v1
kind: PersistentVolumeClaim
metadata:
  name: mongo-pvc
spec:
  storageClassName: mongo
  accessModes:
    - ReadWriteOnce
  resources:
    requests:
      storage: 5Gi

I'm running this on Ubuntu using kubectl and minikube v1.25.1.

When I run describe pod, I see this on the mongodb pod.

Volumes:
  auth-db-storage:
    Type:       PersistentVolumeClaim (a reference to a PersistentVolumeClaim in the same namespace)
    ClaimName:  mongo-pvc
    ReadOnly:   false

I have a similar setup for other pods to store files, and it's working fine. But with mongodb, every time I restart the pods, the data is lost. Can someone help me?

EDIT: I noticed that if I change the mongodb mountPath to /data/db, it works fine. But if I have multiple mongodb pods running on /data/db, they don't work. So I need to have one persistent volume claim for EACH mongodb pod?

user_17739440 · Answer

When using these yaml files, you are mounting the /data/db dir on the minikube node to /data/db/auth in auth-mongo pods.

First, you should change /data/db/auth to /data/db in your k8s deployment so that your mongodb can read the database from the default db location.
Even if you delete the deployment, the db will stay in '/data/db' dir on the minikube node. And after running the new pod from this deployment, mongodb will open this existing db (all data saved).

Second, you can't use multiple mongodb pods like this by just scaling replicas in the deployment because the second mongodb in other Pod can't use already used by the first Pod db. Mongodb will throw this error:

Unable to lock the lock file: /data/db/mongod.lock (Resource temporarily unavailable). Another mongod instance is already running on the /data/db directory

So, the solution is either to use only 1 replica in your deployment or, for example, use MongoDB packaged by Bitnami helm chart. https://github.com/bitnami/charts/tree/master/bitnami/mongodb

This chart bootstraps a MongoDB(®) deployment on a Kubernetes cluster using the Helm package manager.

$ helm install my-release bitnami/mongodb --set architecture=replicaset --set replicaCount=2

Understand MongoDB Architecture Options.

Also, check this link MongoDB Community Kubernetes Operator.

This is a Kubernetes Operator which deploys MongoDB Community into Kubernetes clusters.

My Kubernetes MongoDB service isn't persisting the data

1 Answers