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MongoDB

What is MongoDB

MongoDB is a Kubernetes Custom Resource Definitions (CRD). It provides declarative configuration for MongoDB in a Kubernetes native way. You only need to describe the desired database configuration in a MongoDB object, and the KubeDB operator will create Kubernetes objects in the desired state for you.

MongoDB Spec

As with all other Kubernetes objects, a MongoDB needs apiVersion, kind, and metadata fields. It also needs a .spec section. Below is an example MongoDB object.

apiVersion: kubedb.com/v1alpha1
kind: MongoDB
metadata:
  name: mgo1
  namespace: demo
spec:
  version: 3.4
  storage:
    storageClassName: "standard"
    accessModes:
    - ReadWriteOnce
    resources:
      requests:
        storage: 50Mi
  databaseSecret:
    secretName: mgo1-auth
  nodeSelector:
    disktype: ssd
  init:
    scriptSource:
      gitRepo:
        repository: "https://github.com/kubedb/mongodb-init-scripts.git"
        directory: .
  backupSchedule:
    cronExpression: "@every 6h"
    storageSecretName: mg-snap-secret
    gcs:
      bucket: restic
      prefix: demo
    resources:
      requests:
        memory: "64Mi"
        cpu: "250m"
      limits:
        memory: "128Mi"
        cpu: "500m"
  doNotPause: true
  monitor:
    agent: prometheus.io/coreos-operator
    prometheus:
      namespace: demo
      labels:
        app: kubedb
      interval: 10s
  resources:
    requests:
      memory: "64Mi"
      cpu: "250m"
    limits:
      memory: "128Mi"
      cpu: "500m"

spec.version

spec.version is a required field specifying the version of MongoDB database. Official MongoDB docker images will be used for the specific version.

spec.storage

spec.storage is an optional field that specifies the StorageClass of PVCs dynamically allocated to store data for the database. This storage spec will be passed to the StatefulSet created by KubeDB operator to run database pods. You can specify any StorageClass available in your cluster with appropriate resource requests. If no storage spec is given, an emptyDir is used.

  • spec.storage.storageClassName is the name of the StorageClass used to provision PVCs. PVCs don’t necessarily have to request a class. A PVC with its storageClassName set equal to “” is always interpreted to be requesting a PV with no class, so it can only be bound to PVs with no class (no annotation or one set equal to “”). A PVC with no storageClassName is not quite the same and is treated differently by the cluster depending on whether the DefaultStorageClass admission plugin is turned on.

  • spec.storage.accessModes uses the same conventions as Kubernetes PVCs when requesting storage with specific access modes.

  • spec.storage.resources can be used to request specific quantities of storage. This follows the same resource model used by PVCs.

To learn how to configure spec.storage, please visit the links below:

spec.databaseSecret

spec.databaseSecret is an optional field that points to a Secret used to hold credentials for mongodb super user. If not set, KubeDB operator creates a new Secret {mongodb-object-name}-auth for storing the password for mongodb superuser for each MongoDB object. If you want to use an existing secret please specify that when creating the MongoDB object using spec.databaseSecret.secretName.

This secret contains a user key and a password key which contains the username and password respectively for mongodb superuser. Example:

apiVersion: v1
data:
  password: NnE4dV8yak1PVy1PT1pYaw==
  user: cm9vdA==
kind: Secret
metadata:
  ...
  name: mgo1-auth
  namespace: demo
  ...
type: Opaque

spec.nodeSelector

spec.nodeSelector is an optional field that specifies a map of key-value pairs. For the pod to be eligible to run on a node, the node must have each of the indicated key-value pairs as labels (it can have additional labels as well). To learn more, see here .

spec.init

spec.init is an optional section that can be used to initialize a newly created MongoDB database. MongoDB databases can be initialized in one of two ways:

Initialize via Script

To initialize a MongoDB database using a script (shell script, js script), set the spec.init.scriptSource section when creating a MongoDB object. It will execute files alphabetically with extensions .sh and .js that are found in the repository. ScriptSource must have following information:

Below is an example showing how a shell script from a git repository can be used to initialize a MongoDB database.

apiVersion: kubedb.com/v1alpha1
kind: MongoDB
metadata:
  name: mgo1
spec:
  version: 3.4
  init:
    scriptSource:
      gitRepo:
        repository: "https://github.com/kubedb/mongodb-init-scripts.git"
        directory: .

In the above example, KubeDB operator will launch a Job to execute all js script of mongodb-init-script repo in alphabetical order once StatefulSet pods are running.

Initialize from Snapshots

To initialize from prior snapshots, set the spec.init.snapshotSource section when creating a MongoDB object. In this case, SnapshotSource must have following information:

  • name: Name of the Snapshot

    apiVersion: kubedb.com/v1alpha1
    kind: MongoDB
    metadata:
    name: mgo1
    spec:
    version: 3.4
    init:
    snapshotSource:
      name: "snapshot-xyz"
    

In the above example, MongoDB database will be initialized from Snapshot snapshot-xyz in default namespace. Here, KubeDB operator will launch a Job to initialize MongoDB once StatefulSet pods are running.

spec.backupSchedule

KubeDB supports taking periodic snapshots for MongoDB database. This is an optional section in .spec. When spec.backupSchedule section is added, KubeDB operator immediately takes a backup to validate this information. After that, at each tick kubeDB operator creates a Snapshot object. This triggers operator to create a Job to take backup. If used, set the various sub-fields accordingly.

  • spec.backupSchedule.cronExpression is a required cron expression. This specifies the schedule for backup operations.

  • spec.backupSchedule.{storage} is a required field that is used as the destination for storing snapshot data. KubeDB supports cloud storage providers like S3, GCS, Azure and OpenStack Swift. It also supports any locally mounted Kubernetes volumes, like NFS, Ceph , etc. Only one backend can be used at a time. To learn how to configure this, please visit here.

  • spec.backupSchedule.resources is an optional field that can request compute resources required by Jobs used to take snapshot or initialize databases from snapshot. To learn more, visit here.

spec.doNotPause

spec.doNotPause is an optional field that tells KubeDB operator that if this MongoDB object is deleted, whether it should be reverted automatically. This should be set to true for production databases to avoid accidental deletion. If not set or set to false, deleting a MongoDB object put the database into a dormant state. THe StatefulSet for a DormantDatabase is deleted but the underlying PVCs are left intact. This allows user to resume the database later.

spec.imagePullSecret

KubeDB provides the flexibility of deploying MongoDB database from a private Docker registry. To learn how to deploym MongoDB from a private registry, please visit here.

spec.monitor

MongoDB managed by KubeDB can be monitored with builtin-Prometheus and CoreOS-Prometheus operator out-of-the-box. To learn more,

spec.resources

spec.resources is an optional field. This can be used to request compute resources required by the database pods. To learn more, visit here.

Next Steps

  • Learn how to use KubeDB to run a MongoDB database here.
  • See the list of supported storage providers for snapshots here.
  • Wondering what features are coming next? Please visit here.
  • Want to hack on KubeDB? Check our contribution guidelines.