MongoDB Cluster on Kubernetes 🍃

Kubernetes Operators are application-specific controllers that extend the Kubernetes API to create, configure, and manage instances of stateful applications such as databases. Using the MongoDB Kubernetes Operator, you have full control over your MongoDB deployment from a single Kubernetes control plane, with a consistent experience across different deployment environments.

The Kubernetes Operator manages the typical lifecycle events for a MongoDB cluster: provisioning storage and computing power, configuring network connections, setting up users, and changing these settings as needed.

Prerequisites:

• Kubernetes cluster
• Kubectl
• Helm
• Dynamic volume provisioning

1. Install the Operator

• Add the MongoDB Helm Charts for Kubernetes repository

  helm repo add mongodb https://mongodb.github.io/helm-charts

• Update helm repo

  helm repo update

• By default, this Operator is using cluster name cluster.local, so we want to make sure that we use the correct cluster name or domain. Create a new file values.yaml. Add extra env CLUSTER_DOMAIN inside values.yaml

  operator:
    extraEnvs:
      - name: CLUSTER_DOMAIN
        value: cluster.local

• Finally we install the Operator on namespace 'mongodb'

  helm install community-operator mongodb/community-operator --namespace mongodb --create-namespace -f values.yaml

• Wait untill all resources are running

  # List all resource in ns mongodb
  kubectl get all -n mongodb
  
  # Output
  NAME                                               READY   STATUS    RESTARTS   AGE
  pod/mongodb-kubernetes-operator-77cd5c7c66-xwhx4   1/1     Running   0          39m
  
  NAME                                          READY   UP-TO-DATE   AVAILABLE   AGE
  deployment.apps/mongodb-kubernetes-operator   1/1     1            1           49m
  
  NAME                                                     DESIRED   CURRENT   READY   AGE
  replicaset.apps/mongodb-kubernetes-operator-77cd5c7c66   1         1         1       39m

2. Deploy MongoDB Replica Set Cluster

• Clone mongodb github repository

  git clone https://github.com/mongodb/mongodb-kubernetes-operator.git

• Change directory into mongodb-kubernetes-operator

  cd mongodb-kubernetes-operator/

• Replace <your-password-here> in config/samples/mongodb.com_v1_mongodbcommunity_cr.yaml to the password you wish to use

  [...]
  ---
  apiVersion: v1
  kind: Secret
  metadata:
    name: my-user-password
  type: Opaque
  stringData:
    password: <your-password-here>

• Apply the manifest

  kubectl apply -f config/samples/mongodb.com_v1_mongodbcommunity_cr.yaml --namespace mongodb

• Verify that the MongoDBCommunity resource deployed

  # List all resources in ns mongodb
  watch -d kubectl get all -n mongodb
  
  # Output
  NAME                                               READY   STATUS    RESTARTS   AGE
  pod/example-mongodb-0                              2/2     Running   0          49m
  pod/example-mongodb-1                              2/2     Running   0          49m
  pod/example-mongodb-2                              2/2     Running   0          48m
  pod/mongodb-kubernetes-operator-77cd5c7c66-xwhx4   1/1     Running   0          50m
  
  NAME                          TYPE        CLUSTER-IP   EXTERNAL-IP   PORT(S)     AGE
  service/example-mongodb-svc   ClusterIP   None         <none>        27017/TCP   49m
  
  NAME                                          READY   UP-TO-DATE   AVAILABLE   AGE
  deployment.apps/mongodb-kubernetes-operator   1/1     1            1           60m
  
  NAME                                                     DESIRED   CURRENT   READY   AGE
  replicaset.apps/mongodb-kubernetes-operator-77cd5c7c66   1         1         1       50m
  
  NAME                                   READY   AGE
  statefulset.apps/example-mongodb       3/3     49m
  statefulset.apps/example-mongodb-arb   0/0     49m

• Obtain the MongoDB connection string

  The following command requires jq version 1.6 or higher.

  # Invoke the following kubectl command
  kubectl get secret example-mongodb-admin-my-user -n mongodb -o json | jq -r '.data | with_entries(.value |= @base64d)'
  
  # Output
  {
      "connectionString.standard": "mongodb://<username>:<password>@example-mongodb-0.example-mongodb-svc.mongodb.svc.cluster.local:27017,example-mongodb-1.example-mongodb-svc.mongodb.svc.cluster.local:27017,example-mongodb-2.example-mongodb-svc.mongodb.svc.cluster.local:27017/admin?ssl=true",
      "connectionString.standardSrv": "mongodb+srv://<username>:<password>@example-mongodb-svc.mongodb.svc.cluster.local/admin?ssl=true",
      "password": "<password>",
      "username": "<username>"
  }

• Try connecting to your MongoDB cluster with connectionString.standard above using mongosh from control-plane node. If mongosh not installed on your machine, follow this.

  mongosh "mongodb://<username>:<password>@example-mongodb-0.example-mongodb-svc.mongodb.svc.cluster.local:27017,example-mongodb-1.example-mongodb-svc.mongodb.svc.cluster.local:27017,example-mongodb-2.example-mongodb-svc.mongodb.svc.cluster.local:27017/admin?replicaSet=example-mongodb&ssl=false"
  
  # Output
  Current Mongosh Log ID: 667a7b5e10ee02719a149f47
  Connecting to:          mongodb://<credentials>@example-mongodb-0.example-mongodb-svc.mongodb.svc.cluter.simple:27017,example-mongodb-1.example-mongodb-svc.mongodb.svc.cluter.simple:27017,example-mongodb-2.example-mongodb-svc.mongodb.svc.cluter.simple:27017/admin?replicaSet=example-mongodb&ssl=false&appName=mongosh+2.2.10
  Using MongoDB:          6.0.5
  Using Mongosh:          2.2.10
  
  For mongosh info see: https://docs.mongodb.com/mongodb-shell/
  
  ------
  The server generated these startup warnings when booting
  2024-06-25T07:11:13.373+00:00: Using the XFS filesystem is strongly recommended with the WiredTiger storage engine. See http://dochub.mongodb.org/core/prodnotes-filesystem
  2024-06-25T07:11:17.034+00:00: vm.max_map_count is too low
  ------
  
  example-mongodb [primary] admin>