So, I set a new k8s cluster on DigitalOcean recently, and I want to share the way I deploy my MongoDB Replica Set on the k8s cluster. Let’s start it.
Storage Class
I use Longhorn instead of the default do-block-storage provided by DigitalOcean as the default. I set up the longhorn using the helm chart. Since I use Rancher to manage my cluster, I install Longhorn from the App menu and choose Longhorn with the default value. super simple!
Cluster IP Service
To create a statefulset, we will need to provide the serviceName so, let’s create a ClusterIP service for our MongoDB. The mongodb-clusterip.yaml file looks like this.
kind: Service
metadata:
annotations:
field.cattle.io/description: MongoDB Cluster IP
name: mongodb-clusterip
namespace: default
spec:
ports:
– name: mongo
port: 27017
protocol: TCP
targetPort: 27017
selector:
app: mongodb
type: ClusterIP
Then execute the kubectl apply command
kubectl apply -f mongodb-clusterip.yaml
Secret
We will save the mongodb root user and mongodb root password in the Secret, so we need to create a new Secret for our MongoDB.
The mongodb-secret.yaml file looks like this
data:
password: base6StringVersionOfpassword
user: base6StringVersionOfuser
kind: Secret
metadata:
name: mongodb-secret
namespace: default
Then execute the kubectl apply command
kubectl apply -f mongodb-secret.yaml
StatefulSet
Now the last thing that we need to execute is the statefulset for our MongoDB. The mongodb-statefulset.yaml file looks like this
kind: StatefulSet
metadata:
name: mongodb
namespace: default
spec:
replicas: 2
selector:
matchLabels:
app: mongodb
serviceName: mongodb-clusterip
template:
metadata:
namespace: default
labels:
app: mongodb
spec:
containers:
– args:
– ‘–dbpath’
– /data/db
command:
– mongod
– ‘–bind_ip_all’
– ‘–replSet’
– rs0
env:
– name: MONGO_INITDB_ROOT_USERNAME
valueFrom:
secretKeyRef:
key: user
name: mongodb-secret
– name: MONGO_INITDB_ROOT_PASSWORD
valueFrom:
secretKeyRef:
key: password
name: mongodb-secret
image: mongo:6.0.11
imagePullPolicy: IfNotPresent
name: mongodb-c
volumeMounts:
– mountPath: /data/db
name: mongodb-pvc
volumeClaimTemplates:
– apiVersion: v1
kind: PersistentVolumeClaim
metadata:
name: mongodb-pvc
spec:
accessModes:
– ReadWriteOnce
resources:
requests:
storage: 8Gi
storageClassName: longhorn
Then execute the kubectl apply command
kubectl apply -f mongodb-statefulset.yaml
you can change the replica number with your own. I use 2 here.
After a few minutes, you should see the statefulset created. You can see it in your Rancher or using the kubectl get command.
Let’s make sure that the Mongodb is running using kubectl exec command below.
kubectl –namespace=default exec -ti mongodb-0 — mongosh
Then you should get the mongosh prompt opened. For the second replica, you can do the same by changing the mongodb-0 with mongodb-1 instead.
Configure Replica Set
To configure MongoDB replica set. First we need to open the mongodb-0 (first pod of the MongoDb) using above command.
Then we use the rs.initiate() command as below
{
_id: “rs0”,
members: [
{ _id: 0, host: “mongodb-0.mongodb-clusterip.default.svc.cluster.local:27017” },
{ _id: 1, host: “mongodb-1.mongodb-clusterip.default.svc.cluster.local:27017” }
]
}
)
if you notice that the pattern is <pod>.<service>.<namespace>.svc.cluster.local:port
Then try to add some data to the test db using the query
db.test.insertOne({ testFromMaster: “true” })
Now, exit from the master replica and open the mongosh in the secondary replica using the same command
kubectl –namespace=default exec -ti mongodb-1 — mongosh
You will notice that the prompt is displaying the secondary. To start reading the data changes from the primary replica, we need to run the command
db.getMongo().setReadPref(“primaryPreferred”)
Then we can test to query the test data that we create before using the query
db.test.find({})
Now, you should see the secondary also has the test data.
That’s it. hopefully, you found this useful. Cheers.
