Create and connect to a MongoDB cluster

1. Create a MongoDB cluster.

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

   If you only have one node for deploying a ReplicaSet Cluster, set spec.affinity.topologyKeys as null. But for a production environment, it is not recommended to deploy all replicas on one node, which may decrease the cluster availability.

   cat <<EOF | kubectl apply -f -
   apiVersion: apps.kubeblocks.io/v1alpha1
   kind: Cluster
   metadata:
     name: mycluster
     namespace: demo
   spec:
     terminationPolicy: Delete
     affinity:
       podAntiAffinity: Preferred
       topologyKeys:
       - kubernetes.io/hostname
     tolerations:
       - key: kb-data
         operator: Equal
         value: 'true'
         effect: NoSchedule
     componentSpecs:
     - name: mongodb
       componentDef: mongodb
       replicas: 3
       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.terminationPolicy	It is the policy of cluster termination. The default value is Delete. Valid values are DoNotTerminate, Delete, WipeOut. For the detailed definition, you can refer to Termination Policy.
   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.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
   

2. Verify whether this cluster is created successfully.

   kubectl get cluster mycluster -n demo
   >
   NAME        CLUSTER-DEFINITION   VERSION           TERMINATION-POLICY   STATUS    AGE
   mycluster   mongodb              mongodb-5.0       Delete               Running   12m
   

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