New to KubeDB? Please start here.

MongoDB Sharding

This tutorial will show you how to use KubeDB to run a sharded MongoDB cluster.

Before You Begin

Before proceeding:

  • Read mongodb sharding concept to learn about MongoDB Sharding clustering.

  • You need to have a Kubernetes cluster, and the kubectl command-line tool must be configured to communicate with your cluster. If you do not already have a cluster, you can create one by using kind.

  • Now, install KubeDB cli on your workstation and KubeDB operator in your cluster following the steps here.

  • To keep things isolated, this tutorial uses a separate namespace called demo throughout this tutorial. Run the following command to prepare your cluster for this tutorial:

    $ kubectl create ns demo
    namespace/demo created
    

Note: The yaml files used in this tutorial are stored in docs/examples/mongodb folder in GitHub repository kubedb/docs.

Deploy Sharded MongoDB Cluster

To deploy a MongoDB Sharding, user have to specify spec.replicaSet option in Mongodb CRD.

The following is an example of a Mongodb object which creates MongoDB Sharding of three members.

apiVersion: kubedb.com/v1alpha2
kind: MongoDB
metadata:
  name: mongo-sh
  namespace: demo
spec:
  version: 4.2.3
  shardTopology:
    configServer:
      replicas: 3
      storage:
        resources:
          requests:
            storage: 1Gi
        storageClassName: standard
    mongos:
      replicas: 2
    shard:
      replicas: 3
      shards: 2
      storage:
        resources:
          requests:
            storage: 1Gi
        storageClassName: standard
$ kubectl create -f https://github.com/kubedb/docs/raw/v2021.04.16//docs/examples/mongodb/clustering/mongo-sharding.yaml
mongodb.kubedb.com/mongo-sh created

Here,

  • spec.shardTopology represents the topology configuration for sharding.
    • shard represents configuration for Shard component of mongodb.
      • shards represents number of shards for a mongodb deployment. Each shard is deployed as a replicaset.
      • replicas represents number of replicas of each shard replicaset.
      • prefix represents the prefix of each shard node.
      • configSecret is an optional field to provide custom configuration file for shards (i.e mongod.cnf). If specified, this file will be used as configuration file otherwise a default configuration file will be used.
      • podTemplate is an optional configuration for pods.
      • storage to specify pvc spec for each node of sharding. You can specify any StorageClass available in your cluster with appropriate resource requests.
    • configServer represents configuration for ConfigServer component of mongodb.
      • replicas represents number of replicas for configServer replicaset. Here, configServer is deployed as a replicaset of mongodb.
      • prefix represents the prefix of configServer nodes.
      • configSecret is an optional field to provide custom configuration file for configSource (i.e mongod.cnf). If specified, this file will be used as configuration file otherwise a default configuration file will be used.
      • podTemplate is an optional configuration for pods.
      • storage to specify pvc spec for each node of configServer. You can specify any StorageClass available in your cluster with appropriate resource requests.
    • mongos represents configuration for Mongos component of mongodb. Mongos instances run as stateless components (deployment).
      • replicas represents number of replicas of Mongos instance. Here, Mongos is not deployed as replicaset.
      • prefix represents the prefix of mongos nodes.
      • configSecret is an optional field to provide custom configuration file for mongos (i.e mongod.cnf). If specified, this file will be used as configuration file otherwise a default configuration file will be used.
      • podTemplate is an optional configuration for pods.
  • spec.keyFileSecret (optional) is a secret name that contains keyfile (a random string)against key.txt key. Each mongod instances in the replica set and shardTopology uses the contents of the keyfile as the shared password for authenticating other members in the replicaset. Only mongod instances with the correct keyfile can join the replica set. User can provide the keyFileSecret by creating a secret with key key.txt. See here to create the string for keyFileSecret. If keyFileSecret is not given, KubeDB operator will generate a keyFileSecret itself.

KubeDB operator watches for MongoDB objects using Kubernetes api. When a MongoDB object is created, KubeDB operator will create a new StatefulSet and a Service with the matching MongoDB object name. KubeDB operator will also create governing services for StatefulSets with the name <mongodb-name>-<node-type>-gvr.

MongoDB mongo-sh state,

$ kubectl get mg -n demo
NAME       VERSION   STATUS    AGE
mongo-sh   4.2.3     Ready     9m41s

All the types of nodes Shard, ConfigServer & Mongos are deployed as statefulset.

$ kubectl get statefulset -n demo
NAME                 READY   AGE
mongo-sh-configsvr   3/3     11m
mongo-sh-mongos      3/3     8m41s
mongo-sh-shard0      3/3     10m
mongo-sh-shard1      3/3     8m59s

All PVCs and PVs for MongoDB mongo-sh,

$ kubectl get pvc -n demo
NAME                           STATUS   VOLUME                                     CAPACITY   ACCESS MODES   STORAGECLASS   AGE
datadir-mongo-sh-configsvr-0   Bound    pvc-1db4185e-6a5f-11e9-a871-080027a851ba   1Gi        RWO            standard       16m
datadir-mongo-sh-configsvr-1   Bound    pvc-330cc6ee-6a5f-11e9-a871-080027a851ba   1Gi        RWO            standard       16m
datadir-mongo-sh-configsvr-2   Bound    pvc-3db2d3f5-6a5f-11e9-a871-080027a851ba   1Gi        RWO            standard       15m
datadir-mongo-sh-shard0-0      Bound    pvc-49b7cc3b-6a5f-11e9-a871-080027a851ba   1Gi        RWO            standard       15m
datadir-mongo-sh-shard0-1      Bound    pvc-5b781770-6a5f-11e9-a871-080027a851ba   1Gi        RWO            standard       15m
datadir-mongo-sh-shard0-2      Bound    pvc-6ba3263e-6a5f-11e9-a871-080027a851ba   1Gi        RWO            standard       14m
datadir-mongo-sh-shard1-0      Bound    pvc-75feb227-6a5f-11e9-a871-080027a851ba   1Gi        RWO            standard       14m
datadir-mongo-sh-shard1-1      Bound    pvc-89bb7bb3-6a5f-11e9-a871-080027a851ba   1Gi        RWO            standard       13m
datadir-mongo-sh-shard1-2      Bound    pvc-98c96ae4-6a5f-11e9-a871-080027a851ba   1Gi        RWO            standard       13m


$ kubectl get pv -n demo
NAME                                       CAPACITY   ACCESS MODES   RECLAIM POLICY   STATUS   CLAIM                               STORAGECLASS   REASON   AGE
pvc-1db4185e-6a5f-11e9-a871-080027a851ba   1Gi        RWO            Delete           Bound    demo/datadir-mongo-sh-configsvr-0   standard                17m
pvc-330cc6ee-6a5f-11e9-a871-080027a851ba   1Gi        RWO            Delete           Bound    demo/datadir-mongo-sh-configsvr-1   standard                16m
pvc-3db2d3f5-6a5f-11e9-a871-080027a851ba   1Gi        RWO            Delete           Bound    demo/datadir-mongo-sh-configsvr-2   standard                16m
pvc-49b7cc3b-6a5f-11e9-a871-080027a851ba   1Gi        RWO            Delete           Bound    demo/datadir-mongo-sh-shard0-0      standard                16m
pvc-5b781770-6a5f-11e9-a871-080027a851ba   1Gi        RWO            Delete           Bound    demo/datadir-mongo-sh-shard0-1      standard                15m
pvc-6ba3263e-6a5f-11e9-a871-080027a851ba   1Gi        RWO            Delete           Bound    demo/datadir-mongo-sh-shard0-2      standard                15m
pvc-75feb227-6a5f-11e9-a871-080027a851ba   1Gi        RWO            Delete           Bound    demo/datadir-mongo-sh-shard1-0      standard                14m
pvc-89bb7bb3-6a5f-11e9-a871-080027a851ba   1Gi        RWO            Delete           Bound    demo/datadir-mongo-sh-shard1-1      standard                14m
pvc-98c96ae4-6a5f-11e9-a871-080027a851ba   1Gi        RWO            Delete           Bound    demo/datadir-mongo-sh-shard1-2      standard                13m

Services created for MongoDB mongo-sh

$ kubectl get svc -n demo
NAME                     TYPE        CLUSTER-IP       EXTERNAL-IP   PORT(S)     AGE
mongo-sh                 ClusterIP   10.108.188.201   <none>        27017/TCP   18m
mongo-sh-configsvr-pods  ClusterIP   None             <none>        27017/TCP   18m
mongo-sh-mongos-pods     ClusterIP   None             <none>        27017/TCP   18m
mongo-sh-shard0-pods     ClusterIP   None             <none>        27017/TCP   18m
mongo-sh-shard1-pods     ClusterIP   None             <none>        27017/TCP   18m

KubeDB operator sets the status.phase to Ready once the database is successfully created. It has also defaulted some field of crd object. Run the following command to see the modified MongoDB object:

$ kubectl get mg -n demo mongo-sh -o yaml
apiVersion: kubedb.com/v1alpha2
kind: MongoDB
metadata:
  annotations:
    kubectl.kubernetes.io/last-applied-configuration: |
            {"apiVersion":"kubedb.com/v1alpha2","kind":"MongoDB","metadata":{"annotations":{},"name":"mongo-sh","namespace":"demo"},"spec":{"shardTopology":{"configServer":{"replicas":3,"storage":{"resources":{"requests":{"storage":"1Gi"}},"storageClassName":"standard"}},"mongos":{"replicas":2},"shard":{"replicas":3,"shards":2,"storage":{"resources":{"requests":{"storage":"1Gi"}},"storageClassName":"standard"}}},"version":"4.2.3"}}
  creationTimestamp: "2021-02-10T12:57:03Z"
  finalizers:
    - kubedb.com
  generation: 3
  managedFields:
    - apiVersion: kubedb.com/v1alpha2
      fieldsType: FieldsV1
      fieldsV1:
        f:metadata:
          f:annotations:
            .: {}
            f:kubectl.kubernetes.io/last-applied-configuration: {}
        f:spec:
          .: {}
          f:shardTopology:
            .: {}
            f:configServer:
              .: {}
              f:replicas: {}
              f:storage:
                .: {}
                f:resources:
                  .: {}
                  f:requests:
                    .: {}
                    f:storage: {}
                f:storageClassName: {}
            f:mongos:
              .: {}
              f:replicas: {}
            f:shard:
              .: {}
              f:replicas: {}
              f:shards: {}
              f:storage:
                .: {}
                f:resources:
                  .: {}
                  f:requests:
                    .: {}
                    f:storage: {}
                f:storageClassName: {}
          f:version: {}
      manager: kubectl-client-side-apply
      operation: Update
      time: "2021-02-10T12:57:03Z"
    - apiVersion: kubedb.com/v1alpha2
      fieldsType: FieldsV1
      fieldsV1:
        f:metadata:
          f:finalizers: {}
        f:spec:
          f:authSecret:
            .: {}
            f:name: {}
          f:keyFileSecret:
            .: {}
            f:name: {}
        f:status:
          .: {}
          f:conditions: {}
          f:observedGeneration: {}
          f:phase: {}
      manager: mg-operator
      operation: Update
      time: "2021-02-10T12:57:03Z"
  name: mongo-sh
  namespace: demo
  resourceVersion: "152268"
  uid: 8522c8c1-344b-4824-9061-47031b88f1fa
spec:
  authSecret:
    name: mongo-sh-auth
  clusterAuthMode: keyFile
  keyFileSecret:
    name: mongo-sh-key
  shardTopology:
    configServer:
      podTemplate:
        controller: {}
        metadata: {}
        spec:
          affinity:
            podAntiAffinity:
              preferredDuringSchedulingIgnoredDuringExecution:
                - podAffinityTerm:
                    labelSelector:
                      matchLabels:
                        app.kubernetes.io/instance: mongo-sh
                        app.kubernetes.io/managed-by: kubedb.com
                        app.kubernetes.io/name: mongodbs.kubedb.com
                        mongodb.kubedb.com/node.config: mongo-sh-configsvr
                    namespaces:
                      - demo
                    topologyKey: kubernetes.io/hostname
                  weight: 100
                - podAffinityTerm:
                    labelSelector:
                      matchLabels:
                        app.kubernetes.io/instance: mongo-sh
                        app.kubernetes.io/managed-by: kubedb.com
                        app.kubernetes.io/name: mongodbs.kubedb.com
                        mongodb.kubedb.com/node.config: mongo-sh-configsvr
                    namespaces:
                      - demo
                    topologyKey: failure-domain.beta.kubernetes.io/zone
                  weight: 50
          livenessProbe:
            exec:
              command:
                - bash
                - -c
                - "set -x; if [[ $(mongo admin --host=localhost  --username=$MONGO_INITDB_ROOT_USERNAME
                --password=$MONGO_INITDB_ROOT_PASSWORD --authenticationDatabase=admin
                --quiet --eval \"db.adminCommand('ping').ok\" ) -eq \"1\" ]]; then
                \n          exit 0\n        fi\n        exit 1"
            failureThreshold: 3
            periodSeconds: 10
            successThreshold: 1
            timeoutSeconds: 5
          readinessProbe:
            exec:
              command:
                - bash
                - -c
                - "set -x; if [[ $(mongo admin --host=localhost  --username=$MONGO_INITDB_ROOT_USERNAME
                --password=$MONGO_INITDB_ROOT_PASSWORD --authenticationDatabase=admin
                --quiet --eval \"db.adminCommand('ping').ok\" ) -eq \"1\" ]]; then
                \n          exit 0\n        fi\n        exit 1"
            failureThreshold: 3
            periodSeconds: 10
            successThreshold: 1
            timeoutSeconds: 1
          resources:
            limits:
              cpu: 500m
              memory: 1Gi
            requests:
              cpu: 500m
              memory: 1Gi
          serviceAccountName: mongo-sh
      replicas: 3
      storage:
        resources:
          requests:
            storage: 1Gi
        storageClassName: standard
    mongos:
      podTemplate:
        controller: {}
        metadata: {}
        spec:
          affinity:
            podAntiAffinity:
              preferredDuringSchedulingIgnoredDuringExecution:
                - podAffinityTerm:
                    labelSelector:
                      matchLabels:
                        app.kubernetes.io/instance: mongo-sh
                        app.kubernetes.io/managed-by: kubedb.com
                        app.kubernetes.io/name: mongodbs.kubedb.com
                        mongodb.kubedb.com/node.mongos: mongo-sh-mongos
                    namespaces:
                      - demo
                    topologyKey: kubernetes.io/hostname
                  weight: 100
                - podAffinityTerm:
                    labelSelector:
                      matchLabels:
                        app.kubernetes.io/instance: mongo-sh
                        app.kubernetes.io/managed-by: kubedb.com
                        app.kubernetes.io/name: mongodbs.kubedb.com
                        mongodb.kubedb.com/node.mongos: mongo-sh-mongos
                    namespaces:
                      - demo
                    topologyKey: failure-domain.beta.kubernetes.io/zone
                  weight: 50
          lifecycle:
            preStop:
              exec:
                command:
                  - bash
                  - -c
                  - 'mongo admin --username=$MONGO_INITDB_ROOT_USERNAME --password=$MONGO_INITDB_ROOT_PASSWORD
                  --quiet --eval "db.adminCommand({ shutdown: 1 })" || true'
          livenessProbe:
            exec:
              command:
                - bash
                - -c
                - "set -x; if [[ $(mongo admin --host=localhost  --username=$MONGO_INITDB_ROOT_USERNAME
                --password=$MONGO_INITDB_ROOT_PASSWORD --authenticationDatabase=admin
                --quiet --eval \"db.adminCommand('ping').ok\" ) -eq \"1\" ]]; then
                \n          exit 0\n        fi\n        exit 1"
            failureThreshold: 3
            periodSeconds: 10
            successThreshold: 1
            timeoutSeconds: 5
          readinessProbe:
            exec:
              command:
                - bash
                - -c
                - "set -x; if [[ $(mongo admin --host=localhost  --username=$MONGO_INITDB_ROOT_USERNAME
                --password=$MONGO_INITDB_ROOT_PASSWORD --authenticationDatabase=admin
                --quiet --eval \"db.adminCommand('ping').ok\" ) -eq \"1\" ]]; then
                \n          exit 0\n        fi\n        exit 1"
            failureThreshold: 3
            periodSeconds: 10
            successThreshold: 1
            timeoutSeconds: 1
          resources:
            limits:
              cpu: 500m
              memory: 1Gi
            requests:
              cpu: 500m
              memory: 1Gi
          serviceAccountName: mongo-sh
      replicas: 2
    shard:
      podTemplate:
        controller: {}
        metadata: {}
        spec:
          affinity:
            podAntiAffinity:
              preferredDuringSchedulingIgnoredDuringExecution:
                - podAffinityTerm:
                    labelSelector:
                      matchLabels:
                        app.kubernetes.io/instance: mongo-sh
                        app.kubernetes.io/managed-by: kubedb.com
                        app.kubernetes.io/name: mongodbs.kubedb.com
                        mongodb.kubedb.com/node.shard: mongo-sh-shard${SHARD_INDEX}
                    namespaces:
                      - demo
                    topologyKey: kubernetes.io/hostname
                  weight: 100
                - podAffinityTerm:
                    labelSelector:
                      matchLabels:
                        app.kubernetes.io/instance: mongo-sh
                        app.kubernetes.io/managed-by: kubedb.com
                        app.kubernetes.io/name: mongodbs.kubedb.com
                        mongodb.kubedb.com/node.shard: mongo-sh-shard${SHARD_INDEX}
                    namespaces:
                      - demo
                    topologyKey: failure-domain.beta.kubernetes.io/zone
                  weight: 50
          livenessProbe:
            exec:
              command:
                - bash
                - -c
                - "set -x; if [[ $(mongo admin --host=localhost  --username=$MONGO_INITDB_ROOT_USERNAME
                --password=$MONGO_INITDB_ROOT_PASSWORD --authenticationDatabase=admin
                --quiet --eval \"db.adminCommand('ping').ok\" ) -eq \"1\" ]]; then
                \n          exit 0\n        fi\n        exit 1"
            failureThreshold: 3
            periodSeconds: 10
            successThreshold: 1
            timeoutSeconds: 5
          readinessProbe:
            exec:
              command:
                - bash
                - -c
                - "set -x; if [[ $(mongo admin --host=localhost  --username=$MONGO_INITDB_ROOT_USERNAME
                --password=$MONGO_INITDB_ROOT_PASSWORD --authenticationDatabase=admin
                --quiet --eval \"db.adminCommand('ping').ok\" ) -eq \"1\" ]]; then
                \n          exit 0\n        fi\n        exit 1"
            failureThreshold: 3
            periodSeconds: 10
            successThreshold: 1
            timeoutSeconds: 1
          resources:
            limits:
              cpu: 500m
              memory: 1Gi
            requests:
              cpu: 500m
              memory: 1Gi
          serviceAccountName: mongo-sh
      replicas: 3
      shards: 2
      storage:
        resources:
          requests:
            storage: 1Gi
        storageClassName: standard
  sslMode: disabled
  storageEngine: wiredTiger
  storageType: Durable
  terminationPolicy: Delete
  version: 4.2.3
status:
  conditions:
    - lastTransitionTime: "2021-02-10T12:57:03Z"
      message: 'The KubeDB operator has started the provisioning of MongoDB: demo/mongo-sh'
      reason: DatabaseProvisioningStartedSuccessfully
      status: "True"
      type: ProvisioningStarted
    - lastTransitionTime: "2021-02-10T13:09:44Z"
      message: All desired replicas are ready.
      reason: AllReplicasReady
      status: "True"
      type: ReplicaReady
    - lastTransitionTime: "2021-02-10T12:59:33Z"
      message: 'The MongoDB: demo/mongo-sh is accepting client requests.'
      observedGeneration: 3
      reason: DatabaseAcceptingConnectionRequest
      status: "True"
      type: AcceptingConnection
    - lastTransitionTime: "2021-02-10T12:59:33Z"
      message: 'The MongoDB: demo/mongo-sh is ready.'
      observedGeneration: 3
      reason: ReadinessCheckSucceeded
      status: "True"
      type: Ready
    - lastTransitionTime: "2021-02-10T12:59:51Z"
      message: 'The MongoDB: demo/mongo-sh is successfully provisioned.'
      observedGeneration: 3
      reason: DatabaseSuccessfullyProvisioned
      status: "True"
      type: Provisioned
  observedGeneration: 3
  phase: Ready

Please note that KubeDB operator has created a new Secret called mongo-sh-auth (format: {mongodb-object-name}-auth) for storing the password for mongodb superuser. This secret contains a username key which contains the username for MongoDB superuser and a password key which contains the password for MongoDB superuser.

If you want to use custom or existing secret please specify that when creating the MongoDB object using spec.authSecret.name. While creating this secret manually, make sure the secret contains these two keys containing data username and password. For more details, please see here.

Connection Information

  • Hostname/address: you can use any of these

    • Service: mongo-sh.demo
    • Pod IP: ($ kubectl get po -n demo -l mongodb.kubedb.com/node.mongos=mongo-sh-mongos -o yaml | grep podIP)
  • Port: 27017

  • Username: Run following command to get username,

    $ kubectl get secrets -n demo mongo-sh-auth -o jsonpath='{.data.\username}' | base64 -d
    root
    
  • Password: Run the following command to get password,

    $ kubectl get secrets -n demo mongo-sh-auth -o jsonpath='{.data.\password}' | base64 -d
    7QiqLcuSCmZ8PU5a
    

Now, you can connect to this database through mongo-shell.

Sharded Data

In this tutorial, we will insert sharded and unsharded document, and we will see if the data actually sharded across cluster or not.

$ kubectl get po -n demo -l mongodb.kubedb.com/node.mongos=mongo-sh-mongos
NAME                READY   STATUS    RESTARTS   AGE
mongo-sh-mongos-0   1/1     Running   0          49m
mongo-sh-mongos-1   1/1     Running   0          49m

$ kubectl exec -it mongo-sh-mongos-0 -n demo bash

[email protected]:/$ mongo admin -u root -p 7QiqLcuSCmZ8PU5a
MongoDB shell version v4.2.3
connecting to: mongodb://127.0.0.1:27017/admin?gssapiServiceName=mongodb
Implicit session: session { "id" : UUID("8b7abf57-09e4-4e30-b4a0-a37ebf065e8f") }
MongoDB server version: 4.2.3
Welcome to the MongoDB shell.
For interactive help, type "help".
For more comprehensive documentation, see
	http://docs.mongodb.org/
Questions? Try the support group
	http://groups.google.com/group/mongodb-user
mongos>

To detect if the MongoDB instance that your client is connected to is mongos, use the isMaster command. When a client connects to a mongos, isMaster returns a document with a msg field that holds the string isdbgrid.

mongos> rs.isMaster()
{
	"ismaster" : true,
	"msg" : "isdbgrid",
	"maxBsonObjectSize" : 16777216,
	"maxMessageSizeBytes" : 48000000,
	"maxWriteBatchSize" : 100000,
	"localTime" : ISODate("2021-02-10T13:37:24.140Z"),
	"logicalSessionTimeoutMinutes" : 30,
	"connectionId" : 803,
	"maxWireVersion" : 8,
	"minWireVersion" : 0,
	"ok" : 1,
	"operationTime" : Timestamp(1612964237, 2),
	"$clusterTime" : {
		"clusterTime" : Timestamp(1612964237, 2),
		"signature" : {
			"hash" : BinData(0,"5ugX3jIC+sVDtYjxGWP5SCI7QSE="),
			"keyId" : NumberLong("6927618399740624913")
		}
	}
}

mongo-sh Shard status,

mongos> sh.status()
--- Sharding Status --- 
  sharding version: {
  	"_id" : 1,
  	"minCompatibleVersion" : 5,
  	"currentVersion" : 6,
  	"clusterId" : ObjectId("6023d83b8df2b687ecfade84")
  }
  shards:
        {  "_id" : "shard0",  "host" : "shard0/mongo-sh-shard0-0.mongo-sh-shard0-pods.demo.svc.cluster.local:27017,mongo-sh-shard0-1.mongo-sh-shard0-pods.demo.svc.cluster.local:27017,mongo-sh-shard0-2.mongo-sh-shard0-pods.demo.svc.cluster.local:27017",  "state" : 1 }
        {  "_id" : "shard1",  "host" : "shard1/mongo-sh-shard1-0.mongo-sh-shard1-pods.demo.svc.cluster.local:27017,mongo-sh-shard1-1.mongo-sh-shard1-pods.demo.svc.cluster.local:27017,mongo-sh-shard1-2.mongo-sh-shard1-pods.demo.svc.cluster.local:27017",  "state" : 1 }
  active mongoses:
        "4.2.3" : 2
  autosplit:
        Currently enabled: yes
  balancer:
        Currently enabled:  yes
        Currently running:  no
        Failed balancer rounds in last 5 attempts:  0
        Migration Results for the last 24 hours: 
                No recent migrations
  databases:
        {  "_id" : "config",  "primary" : "config",  "partitioned" : true }
                config.system.sessions
                        shard key: { "_id" : 1 }
                        unique: false
                        balancing: true
                        chunks:
                                shard0	1
                        { "_id" : { "$minKey" : 1 } } -->> { "_id" : { "$maxKey" : 1 } } on : shard0 Timestamp(1, 0) 

Shard collection test.testcoll and insert document. See sh.shardCollection(namespace, key, unique, options) for details about shardCollection command.

mongos> sh.enableSharding("test");
{
	"ok" : 1,
	"operationTime" : Timestamp(1612964293, 5),
	"$clusterTime" : {
		"clusterTime" : Timestamp(1612964293, 5),
		"signature" : {
			"hash" : BinData(0,"DJbXhWUbiTQCWvlWgTTW/vlH3LE="),
			"keyId" : NumberLong("6927618399740624913")
		}
	}
}

mongos> sh.shardCollection("test.testcoll", {"myfield": 1});
{
	"collectionsharded" : "test.testcoll",
	"collectionUUID" : UUID("f2617eb1-8f61-47dd-af58-73f5fe4ea2c0"),
	"ok" : 1,
	"operationTime" : Timestamp(1612964314, 14),
	"$clusterTime" : {
		"clusterTime" : Timestamp(1612964314, 14),
		"signature" : {
			"hash" : BinData(0,"CZzOATrFeADxMkGTWbX85Olkc2Q="),
			"keyId" : NumberLong("6927618399740624913")
		}
	}
}

mongos> use test;
switched to db test

mongos> db.testcoll.insert({"myfield": "a", "otherfield": "b"});
WriteResult({ "nInserted" : 1 })

mongos> db.testcoll.insert({"myfield": "c", "otherfield": "d", "kube" : "db" });
WriteResult({ "nInserted" : 1 })

mongos> db.testcoll.find();
{ "_id" : ObjectId("5cc6d6f656a9ddd30be2c12a"), "myfield" : "a", "otherfield" : "b" }
{ "_id" : ObjectId("5cc6d71e56a9ddd30be2c12b"), "myfield" : "c", "otherfield" : "d", "kube" : "db" }

Run sh.status() to see whether the test database has sharding enabled, and the primary shard for the test database.

The Sharded Collection section sh.status.databases.<collection> provides information on the sharding details for sharded collection(s) (E.g. test.testcoll). For each sharded collection, the section displays the shard key, the number of chunks per shard(s), the distribution of documents across chunks, and the tag information, if any, for shard key range(s).

mongos> sh.status();
--- Sharding Status --- 
  sharding version: {
  	"_id" : 1,
  	"minCompatibleVersion" : 5,
  	"currentVersion" : 6,
  	"clusterId" : ObjectId("6023d83b8df2b687ecfade84")
  }
  shards:
        {  "_id" : "shard0",  "host" : "shard0/mongo-sh-shard0-0.mongo-sh-shard0-pods.demo.svc.cluster.local:27017,mongo-sh-shard0-1.mongo-sh-shard0-pods.demo.svc.cluster.local:27017,mongo-sh-shard0-2.mongo-sh-shard0-pods.demo.svc.cluster.local:27017",  "state" : 1 }
        {  "_id" : "shard1",  "host" : "shard1/mongo-sh-shard1-0.mongo-sh-shard1-pods.demo.svc.cluster.local:27017,mongo-sh-shard1-1.mongo-sh-shard1-pods.demo.svc.cluster.local:27017,mongo-sh-shard1-2.mongo-sh-shard1-pods.demo.svc.cluster.local:27017",  "state" : 1 }
  active mongoses:
        "4.2.3" : 2
  autosplit:
        Currently enabled: yes
  balancer:
        Currently enabled:  yes
        Currently running:  no
        Failed balancer rounds in last 5 attempts:  0
        Migration Results for the last 24 hours: 
                No recent migrations
  databases:
        {  "_id" : "config",  "primary" : "config",  "partitioned" : true }
                config.system.sessions
                        shard key: { "_id" : 1 }
                        unique: false
                        balancing: true
                        chunks:
                                shard0	1
                        { "_id" : { "$minKey" : 1 } } -->> { "_id" : { "$maxKey" : 1 } } on : shard0 Timestamp(1, 0) 
        {  "_id" : "test",  "primary" : "shard1",  "partitioned" : true,  "version" : {  "uuid" : UUID("2a39d8c7-c731-46af-84c3-bf04ba10ac82"),  "lastMod" : 1 } }
                test.testcoll
                        shard key: { "myfield" : 1 }
                        unique: false
                        balancing: true
                        chunks:
                                shard1	1
                        { "myfield" : { "$minKey" : 1 } } -->> { "myfield" : { "$maxKey" : 1 } } on : shard1 Timestamp(1, 0) 

Now create another database where partiotioned is not applied and see how the data is stored.

mongos> use demo
switched to db demo

mongos> db.testcoll2.insert({"myfield": "ccc", "otherfield": "d", "kube" : "db" });
WriteResult({ "nInserted" : 1 })

mongos> db.testcoll2.insert({"myfield": "aaa", "otherfield": "d", "kube" : "db" });
WriteResult({ "nInserted" : 1 })


mongos> db.testcoll2.find()
{ "_id" : ObjectId("5cc6dc831b6d9b3cddc947ec"), "myfield" : "ccc", "otherfield" : "d", "kube" : "db" }
{ "_id" : ObjectId("5cc6dce71b6d9b3cddc947ed"), "myfield" : "aaa", "otherfield" : "d", "kube" : "db" }

Now, eventually sh.status()

mongos> sh.status()
--- Sharding Status --- 
  sharding version: {
  	"_id" : 1,
  	"minCompatibleVersion" : 5,
  	"currentVersion" : 6,
  	"clusterId" : ObjectId("6023d83b8df2b687ecfade84")
  }
  shards:
        {  "_id" : "shard0",  "host" : "shard0/mongo-sh-shard0-0.mongo-sh-shard0-pods.demo.svc.cluster.local:27017,mongo-sh-shard0-1.mongo-sh-shard0-pods.demo.svc.cluster.local:27017,mongo-sh-shard0-2.mongo-sh-shard0-pods.demo.svc.cluster.local:27017",  "state" : 1 }
        {  "_id" : "shard1",  "host" : "shard1/mongo-sh-shard1-0.mongo-sh-shard1-pods.demo.svc.cluster.local:27017,mongo-sh-shard1-1.mongo-sh-shard1-pods.demo.svc.cluster.local:27017,mongo-sh-shard1-2.mongo-sh-shard1-pods.demo.svc.cluster.local:27017",  "state" : 1 }
  active mongoses:
        "4.2.3" : 2
  autosplit:
        Currently enabled: yes
  balancer:
        Currently enabled:  yes
        Currently running:  no
        Failed balancer rounds in last 5 attempts:  0
        Migration Results for the last 24 hours: 
                No recent migrations
  databases:
        {  "_id" : "config",  "primary" : "config",  "partitioned" : true }
                config.system.sessions
                        shard key: { "_id" : 1 }
                        unique: false
                        balancing: true
                        chunks:
                                shard0	1
                        { "_id" : { "$minKey" : 1 } } -->> { "_id" : { "$maxKey" : 1 } } on : shard0 Timestamp(1, 0) 
        {  "_id" : "demo",  "primary" : "shard1",  "partitioned" : false,  "version" : {  "uuid" : UUID("93d077e0-2da0-4b68-a4d4-d23394b22ab2"),  "lastMod" : 1 } }
        {  "_id" : "test",  "primary" : "shard1",  "partitioned" : true,  "version" : {  "uuid" : UUID("2a39d8c7-c731-46af-84c3-bf04ba10ac82"),  "lastMod" : 1 } }
                test.testcoll
                        shard key: { "myfield" : 1 }
                        unique: false
                        balancing: true
                        chunks:
                                shard1	1
                        { "myfield" : { "$minKey" : 1 } } -->> { "myfield" : { "$maxKey" : 1 } } on : shard1 Timestamp(1, 0) 

Here, demo database is not partitioned and all collections under demo database are stored in it’s primary shard, which is shard1.

Halt Database

When TerminationPolicy is set to halt, and you delete the mongodb object, the KubeDB operator will delete the StatefulSet and its pods but leaves the PVCs, secrets and database backup (snapshots) intact. Learn details of all TerminationPolicy here.

You can also keep the mongodb object and halt the database to resume it again later. If you halt the database, the kubedb will delete the statefulsets and services but will keep the mongodb object, pvcs, secrets and backup (snapshots).

To halt the database, first you have to set the terminationPolicy to Halt in existing database. You can use the below command to set the terminationPolicy to Halt, if it is not already set.

$ kubectl patch -n demo mg/mongo-sh -p '{"spec":{"terminationPolicy":"Halt"}}' --type="merge"
mongodb.kubedb.com/mongo-sh patched

Then, you have to set the spec.halted as true to set the database in a Halted state. You can use the below command.

$ kubectl patch -n demo mg/mongo-sh -p '{"spec":{"halted":true}}' --type="merge"
mongodb.kubedb.com/mongo-sh patched

After that, kubedb will delete the statefulsets and services and you can see the database Phase as Halted.

Now, you can run the following command to get all mongodb resources in demo namespaces,

$ kubectl get mg,sts,svc,secret,pvc -n demo
NAME                          VERSION   STATUS   AGE
mongodb.kubedb.com/mongo-sh   4.2.3     Halted   74m

NAME                            TYPE                                  DATA   AGE
secret/default-token-x2zcl      kubernetes.io/service-account-token   3      32h
secret/mongo-sh-auth            Opaque                                2      75m
secret/mongo-sh-key             Opaque                                1      75m

NAME                                                 STATUS   VOLUME                                     CAPACITY   ACCESS MODES   STORAGECLASS   AGE
persistentvolumeclaim/datadir-mongo-sh-configsvr-0   Bound    pvc-9d1b3c01-fdce-45ab-b6f6-fc7bf9462e89   1Gi        RWO            standard       74m
persistentvolumeclaim/datadir-mongo-sh-configsvr-1   Bound    pvc-8e14fcea-ec15-4614-9ec5-21fdf3eb477c   1Gi        RWO            standard       74m
persistentvolumeclaim/datadir-mongo-sh-configsvr-2   Bound    pvc-b65665ce-f35b-4c4f-a7ac-410ad2dfa82d   1Gi        RWO            standard       73m
persistentvolumeclaim/datadir-mongo-sh-shard0-0      Bound    pvc-8fbfdd01-1ed1-4e3b-9a2a-0aa75911cbf0   1Gi        RWO            standard       74m
persistentvolumeclaim/datadir-mongo-sh-shard0-1      Bound    pvc-71d2b22b-2168-46d3-927c-d3ac92f22ebb   1Gi        RWO            standard       74m
persistentvolumeclaim/datadir-mongo-sh-shard0-2      Bound    pvc-82f83359-6e31-43e4-88b3-2555cb442ca0   1Gi        RWO            standard       73m
persistentvolumeclaim/datadir-mongo-sh-shard1-0      Bound    pvc-07ef7cd3-99b2-47de-b1bb-ef6c5606d92e   1Gi        RWO            standard       74m
persistentvolumeclaim/datadir-mongo-sh-shard1-1      Bound    pvc-ffa4b9a7-2492-4f18-be90-7950004e9efd   1Gi        RWO            standard       74m
persistentvolumeclaim/datadir-mongo-sh-shard1-2      Bound    pvc-4e75b90e-dac5-4431-a50e-2bc8dfcf481b   1Gi        RWO            standard       73m

From the above output, you can see that MongoDB object, PVCs, Secret are still there.

Resume Halted Database

Now, to resume the database, i.e. to get the same database setup back again, you have to set the the spec.halted as false. You can use the below command.

$ kubectl patch -n demo mg/mongo-sh -p '{"spec":{"halted":false}}' --type="merge"
mongodb.kubedb.com/mongo-sh patched

When the database is resumed successfully, you can see the database Status is set to Ready.

$ kubectl get mg -n demo
NAME       VERSION   STATUS    AGE
mongo-sh   4.2.3     Ready     6m27s

Now, If you again exec into pod and look for previous data, you will see that, all the data persists.

$ kubectl get po -n demo -l mongodb.kubedb.com/node.mongos=mongo-sh-mongos
NAME                READY   STATUS    RESTARTS   AGE
mongo-sh-mongos-0   1/1     Running   0          3m52s
mongo-sh-mongos-1   1/1     Running   0          3m52s


$ kubectl exec -it mongo-sh-mongos-0 -n demo bash

[email protected]:/$ mongo admin -u root -p 7QiqLcuSCmZ8PU5a

mongos> use test;
switched to db test

mongos> db.testcoll.find();
{ "_id" : ObjectId("5cc6d6f656a9ddd30be2c12a"), "myfield" : "a", "otherfield" : "b" }
{ "_id" : ObjectId("5cc6d71e56a9ddd30be2c12b"), "myfield" : "c", "otherfield" : "d", "kube" : "db" }

mongos> sh.status()
--- Sharding Status --- 
  sharding version: {
  	"_id" : 1,
  	"minCompatibleVersion" : 5,
  	"currentVersion" : 6,
  	"clusterId" : ObjectId("6023d83b8df2b687ecfade84")
  }
  shards:
        {  "_id" : "shard0",  "host" : "shard0/mongo-sh-shard0-0.mongo-sh-shard0-pods.demo.svc.cluster.local:27017,mongo-sh-shard0-1.mongo-sh-shard0-pods.demo.svc.cluster.local:27017,mongo-sh-shard0-2.mongo-sh-shard0-pods.demo.svc.cluster.local:27017",  "state" : 1 }
        {  "_id" : "shard1",  "host" : "shard1/mongo-sh-shard1-0.mongo-sh-shard1-pods.demo.svc.cluster.local:27017,mongo-sh-shard1-1.mongo-sh-shard1-pods.demo.svc.cluster.local:27017,mongo-sh-shard1-2.mongo-sh-shard1-pods.demo.svc.cluster.local:27017",  "state" : 1 }
  active mongoses:
        "4.2.3" : 2
  autosplit:
        Currently enabled: yes
  balancer:
        Currently enabled:  yes
        Currently running:  no
        Failed balancer rounds in last 5 attempts:  1
        Last reported error:  Could not find host matching read preference { mode: "primary" } for set shard0
        Time of Reported error:  Wed Feb 10 2021 14:16:04 GMT+0000 (UTC)
        Migration Results for the last 24 hours: 
                No recent migrations
  databases:
        {  "_id" : "config",  "primary" : "config",  "partitioned" : true }
                config.system.sessions
                        shard key: { "_id" : 1 }
                        unique: false
                        balancing: true
                        chunks:
                                shard0	1
                        { "_id" : { "$minKey" : 1 } } -->> { "_id" : { "$maxKey" : 1 } } on : shard0 Timestamp(1, 0) 
        {  "_id" : "demo",  "primary" : "shard1",  "partitioned" : false,  "version" : {  "uuid" : UUID("93d077e0-2da0-4b68-a4d4-d23394b22ab2"),  "lastMod" : 1 } }
        {  "_id" : "test",  "primary" : "shard1",  "partitioned" : true,  "version" : {  "uuid" : UUID("2a39d8c7-c731-46af-84c3-bf04ba10ac82"),  "lastMod" : 1 } }
                test.testcoll
                        shard key: { "myfield" : 1 }
                        unique: false
                        balancing: true
                        chunks:
                                shard1	1
                        { "myfield" : { "$minKey" : 1 } } -->> { "myfield" : { "$maxKey" : 1 } } on : shard1 Timestamp(1, 0)

Cleaning up

To cleanup the Kubernetes resources created by this tutorial, run:

kubectl patch -n demo mg/mongo-sh -p '{"spec":{"terminationPolicy":"WipeOut"}}' --type="merge"
kubectl delete -n demo mg/mongo-sh

kubectl delete ns demo

Next Steps