Create and connect to a MongoDB cluster

This tutorial shows how to create and connect to a MongoDB cluster.

Create a MongoDB cluster

Before you start

• Install KubeBlocks.

• View all the database types and versions available for creating a cluster.

  Make sure the mongodb cluster definition is installed. If the cluster definition is not available, refer to this doc to enable it first.

  kubectl get clusterdefinition mongodb
  >
  NAME      TOPOLOGIES   SERVICEREFS   STATUS      AGE
  mongodb                              Available   30m

  View all available versions for creating a cluster.

  kubectl get clusterversions -l clusterdefinition.kubeblocks.io/name=mongodb

• To keep things isolated, create a separate namespace called demo throughout this tutorial.

  kubectl create namespace demo

Create a cluster

KubeBlocks supports creating two types of MongoDB clusters: Standalone and ReplicaSet. Standalone only supports one replica and can be used in scenarios with lower requirements for availability. For scenarios with high availability requirements, it is recommended to create a ReplicaSet, which creates a cluster with three replicas to support automatic failover.

To ensure high availability, all replicas are distributed on different nodes by default. If you only have one node for deploying a ReplicaSet Cluster, set spec.affinity.topologyKeys as null.

KubeBlocks implements a Cluster CRD to define a cluster. Here is an example of creating a MongoDB Standalone.

cat <<EOF | kubectl apply -f -
apiVersion: apps.kubeblocks.io/v1alpha1
kind: Cluster
metadata:
  name: mycluster
  namespace: demo
spec:
  clusterDefinitionRef: mongodb
  clusterVersionRef: mongodb-6.0
  terminationPolicy: Delete
  affinity:
    podAntiAffinity: Preferred
    topologyKeys:
    - kubernetes.io/hostname
  tolerations:
    - key: kb-data
      operator: Equal
      value: 'true'
      effect: NoSchedule
  componentSpecs:
  - name: mongodb
    componentDefRef: mongodb
    enabledLogs:
    - running
    disableExporter: true
    serviceAccountName: kb-mongo-cluster
    replicas: 1
    resources:
      limits:
        cpu: '0.5'
        memory: 0.5Gi
      requests:
        cpu: '0.5'
        memory: 0.5Gi
    volumeClaimTemplates:
    - name: data
      spec:
        accessModes:
        - ReadWriteOnce
        resources:
          requests:
            storage: 20Gi
EOF

Field	Definition
spec.clusterDefinitionRef	It specifies the name of the ClusterDefinition for creating a specific type of cluster.
spec.clusterVersionRef	It is the name of the cluster version CRD that defines the cluster version.
spec.terminationPolicy	It is the policy of cluster termination. The default value is Delete. Valid values are DoNotTerminate, Halt, Delete, WipeOut. - DoNotTerminate blocks deletion operation. - Halt deletes workload resources such as statefulset and deployment workloads but keep PVCs. - Delete is based on Halt and deletes PVCs. - WipeOut is based on Delete and wipe out all volume snapshots and snapshot data from a backup storage location.
spec.affinity	It defines a set of node affinity scheduling rules for the cluster's Pods. This field helps control the placement of Pods on nodes within the cluster.
spec.affinity.podAntiAffinity	It specifies the anti-affinity level of Pods within a component. It determines how pods should spread across nodes to improve availability and performance.
spec.affinity.topologyKeys	It represents the key of node labels used to define the topology domain for Pod anti-affinity and Pod spread constraints.
spec.tolerations	It is an array that specifies tolerations attached to the cluster's Pods, allowing them to be scheduled onto nodes with matching taints.
spec.componentSpecs	It is the list of components that define the cluster components. This field allows customized configuration of each component within a cluster.
spec.componentSpecs.componentDefRef	It is the name of the component definition that is defined in the cluster definition and you can get the component definition names with kubectl get clusterdefinition mongodb -o json \| jq '.spec.componentDefs[].name'.
spec.componentSpecs.name	It specifies the name of the component.
spec.componentSpecs.disableExporter	It defines whether the monitoring function is enabled.
spec.componentSpecs.replicas	It specifies the number of replicas of the component.
spec.componentSpecs.resources	It specifies the resource requirements of the component.

KubeBlocks operator watches for the Cluster CRD and creates the cluster and all dependent resources. You can get all the resources created by the cluster by running the command below.

kubectl get all,secret,rolebinding,serviceaccount -l app.kubernetes.io/instance=mycluster -n demo

Run the following command to view the created MongoDB cluster object.

kubectl get cluster mycluster -n demo -o yaml

Output

apiVersion: apps.kubeblocks.io/v1alpha1
kind: Cluster
metadata:
  annotations:
    kubectl.kubernetes.io/last-applied-configuration: |
      {"apiVersion":"apps.kubeblocks.io/v1alpha1","kind":"Cluster","metadata":{"annotations":{},"labels":{"app.kubernetes.io/instance":"mycluster","app.kubernetes.io/version":"5.0.14","helm.sh/chart":"mycluster-0.8.0"},"name":"mycluster","namespace":"demo"},"spec":{"affinity":{"podAntiAffinity":"Preferred","topologyKeys":["kubernetes.io/hostname"]},"clusterDefinitionRef":"mongodb","clusterVersionRef":"mongodb-5.0","componentSpecs":[{"componentDefRef":"mongodb","disableExporter":true,"name":"mongodb","replicas":1,"resources":{"limits":{"cpu":"0.5","memory":"0.5Gi"},"requests":{"cpu":"0.5","memory":"0.5Gi"}},"serviceAccountName":null,"services":null,"volumeClaimTemplates":[{"name":"data","spec":{"accessModes":["ReadWriteOnce"],"resources":{"requests":{"storage":"20Gi"}}}}]}],"terminationPolicy":"Delete"}}
  creationTimestamp: "2024-05-07T10:23:13Z"
  finalizers:
  - cluster.kubeblocks.io/finalizer
  generation: 1
  labels:
    app.kubernetes.io/instance: mycluster
    app.kubernetes.io/version: 5.0.14
    clusterdefinition.kubeblocks.io/name: mongodb
    clusterversion.kubeblocks.io/name: mongodb-5.0
    helm.sh/chart: mongodb-cluster-0.8.0
  name: mycluster
  namespace: demo
  resourceVersion: "560727"
  uid: 3fced3b6-34bf-4d3a-88e2-baf4e2d73b44
spec:
  affinity:
    podAntiAffinity: Preferred
    topologyKeys:
    - kubernetes.io/hostname
  clusterDefinitionRef: mongodb
  clusterVersionRef: mongodb-5.0
  componentSpecs:
  - componentDefRef: mongodb
    disableExporter: true
    name: mongodb
    replicas: 1
    resources:
      limits:
        cpu: "0.5"
        memory: 0.5Gi
      requests:
        cpu: "0.5"
        memory: 0.5Gi
    volumeClaimTemplates:
    - name: data
      spec:
        accessModes:
        - ReadWriteOnce
        resources:
          requests:
            storage: 20Gi
  terminationPolicy: Delete
status:
  clusterDefGeneration: 2
  components:
    mongodb:
      phase: Running
      podsReady: true
      podsReadyTime: "2024-05-07T10:23:55Z"
  conditions:
  - lastTransitionTime: "2024-05-07T10:23:13Z"
    message: 'The operator has started the provisioning of Cluster: mycluster'
    observedGeneration: 1
    reason: PreCheckSucceed
    status: "True"
    type: ProvisioningStarted
  - lastTransitionTime: "2024-05-07T10:23:13Z"
    message: Successfully applied for resources
    observedGeneration: 1
    reason: ApplyResourcesSucceed
    status: "True"
    type: ApplyResources
  - lastTransitionTime: "2024-05-07T10:23:55Z"
    message: all pods of components are ready, waiting for the probe detection successful
    reason: AllReplicasReady
    status: "True"
    type: ReplicasReady
  - lastTransitionTime: "2024-05-07T10:23:55Z"
    message: 'Cluster: mycluster is ready, current phase is Running'
    reason: ClusterReady
    status: "True"
    type: Ready
  observedGeneration: 1
  phase: Running

Connect to a MongoDB Cluster

kubectl

You can use kubectl exec to exec into a Pod and connect to a database.

KubeBlocks operator has created a new Secret called mycluster-conn-credential to store the connection credential of the MongoDB cluster. This secret contains the following keys:

• username: the root username of the MongoDB cluster.
• password: the password of the root user.
• port: the port of the MongoDB cluster.
• host: the host of the MongoDB cluster.
• endpoint: the endpoint of the MongoDB cluster and it is the same as host:port.

1. Get the username and password to connect to this MongoDB cluster for the kubectl exec command.

   kubectl get secrets -n demo mycluster-conn-credential -o jsonpath='{.data.\username}' | base64 -d
   >
   root
   
   kubectl get secrets -n demo mycluster-conn-credential -o jsonpath='{.data.\password}' | base64 -d
   >
   266zfqx5

2. Exec into the Pod mycluster-mongodb-0 and connect to the database using username and password.

   kubectl exec -ti -n demo mycluster-mongodb-0 -- bash
   
   root@mycluster-mongodb-0:/# mongo --username root --password 266zfqx5 --authenticationDatabase admin

port-forward

You can also port forward the service to connect to the database from your local machine.

1. Run the following command to port forward the service.

   kubectl port-forward -n demo svc/mycluster-mongodb 27017:27017  

2. Open a new terminal and run the following command to connect to the database.

   root@mycluster-mongodb-0:/# mongo --username root --password 266zfqx5 --authenticationDatabase admin

For the detailed database connection guide, refer to Connect database.