How to Make use of a MongoDB Database with the StatefulSets on Google Kubernetes Engine

John C TaylorSeptember 15th 2021, 11:55

You wish to run the MongoDB on the Google Cloud Kubernetes Engine that demands access to the persistent disk.

Given that MongoDB demands a persistent disk, you should deploy it as a stateful application. This demands that you make use of the StateFulSet controller to roll out the MongoDB for a persistent identity whenever the pods have to be rescheduled or started out afresh.

These steps will certainly help out:

Step 1 : Sign in to the console of Google Cloud

Step 2 : Set up the Google Cloud shell

Step 3 : Run the command below to initiate a hello-world cluster:

gcloud container clusters create hello-world \
    --region us-east1

Step 4 : The command takes quite some time to run

Step 5 : Run these commands to generate your StorageClass which instructs the Kubernetes the kind of disk you want for your MongoDB database:


mkdir StatefulSet
cd StatefulSet
cat >> googlecloud_ssd.yaml <<EOL
kind: StorageClass
apiVersion: storage.k8s.io/v1
metadata:
  name: fast
provisioner: kubernetes.io/gce-pd
parameters:
  type: pd-ssd
EOL

Step 6 : Run these commands to apply the StorageClass to the Kubernetes:

kubectl apply -f googlecloud_ssd.yaml

Step 7 : In the terms that govern the use of Kubernetes, ‘service’ denotes the set of rules or policies that oversee the access of specific pods. To summarize, a headless service is one that does not vouch for the servicing of the load.

Step 8 : When used alongside the StatefulSet, this grants the individual DNSs that you use to access the pods, and in return, a means by which you connect all your MongoDB nodes one at a time.

Step 9 : Run the command below to generate the mongo-statefulset.yaml file. You may also gain access to this code at:

cat >> mongo-statefulset.yaml <<EOL
apiVersion: v1
kind: Service
metadata:
  name: mongo
  labels:
    name: mongo
spec:
  ports:
  - port: 27017
    targetPort: 27017
  clusterIP: None
  selector:
    role: mongo
---
apiVersion: apps/v1
kind: StatefulSet
metadata:
  name: mongo
spec:
  serviceName: "mongo"
  replicas: 3
  selector:
    matchLabels:
      role: mongo
  template:
    metadata:
      labels:
        role: mongo
        environment: test
        replicaset: MainRepSet
    spec:
      terminationGracePeriodSeconds: 10
      containers:
        - name: mongo
          image: mongo
          command:
            - "mongod"
            - "--bind_ip"
            - "0.0.0.0"
            - "--replSet"
            - "MainRepSet"
          resources:
            requests:
              cpu: 0.2
              memory: 200Mi
          ports:
            - containerPort: 27017
          volumeMounts:
            - name: mongo-persistent-storage
              mountPath: /data/db
  volumeClaimTemplates:
  - metadata:
      name: mongo-persistent-storage
      annotations:
        volume.beta.kubernetes.io/storage-class: "fast"
    spec:
      accessModes: [ "ReadWriteOnce" ]
      resources:
        requests:
          storage: 10Gi
EOL

Step 10 : To set up the Headless Service and the StatefulSet, run this command:

kubectl apply -f mongo-statefulset.yaml

Step 11 : Before interconnecting the MongoDB replica set, you have to validate that it is indeed running by invoking the following command:

kubectl get statefulset

Step 12 : You shall receive this input:

Step 13 : To generate the list of the pods in your cluster, run the command below:

kubectl get pods

Step 14 : Interconnect it to the first set of the replica:

kubectl exec -it mongo-0 -c mongo bash

Step 15 : To operationalize the replica set, run this command below:

mongo
rs.initiate()
exit

Step 16 : Just if you may have to upscale the replica set, run the command below to up the replica set from 3 to 5

kubectl scale --replicas=5 statefulset mongo

Step 17 : If on the other hand, you need to downscale the replica set, run this command as it decreases the set from 5 to 3.

kubectl scale --replicas=3 statefulset mongo

Step 18 : You should now go-ahead to connect your MongoDB replica set by adopting the URI formatting below:

"mongodb://mongo-0.mongo,mongo-1.mongo,mongo-2.mongo:27017/dbname_?"

Step 19 : Each pod that constitutes the StatefulSet is backed by a Headless Service that possesses a stable DNS name. Its template follows this format : <pod-name >.< service-name>

In this instance, you deployed MongoDB as a form of stateful application. The use of the Headless service empowers you to delineate policies or instructions for accessing specific pods. Nonetheless, it does not recommend load balancing.