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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/v1alpha2
kind: MongoDB
metadata:
  name: mgo1
  namespace: demo
spec:
  version: "3.4-v3"
  replicas: 3
  authSecret:
    name: mgo1-auth
  replicaSet:
    name: rs0
  shardTopology:
    configServer:
      podTemplate: {}
      replicas: 3
      storage:
        dataSource: null
        resources:
          requests:
            storage: 1Gi
        storageClassName: standard
    mongos:
      podTemplate: {}
      replicas: 2
      strategy:
        type: RollingUpdate
    shard:
      podTemplate: {}
      replicas: 3
      shards: 3
      storage:
        dataSource: null
        resources:
          requests:
            storage: 1Gi
        storageClassName: standard
  sslMode: preferSSL
  tls:
    issuerRef:
      name: mongo-ca-issuer
      kind: Issuer
      apiGroup: "cert-manager.io"
    certificate:
      organization:
        - kubedb
  clusterAuthMode: x509
  storageType: "Durable"
  storage:
    storageClassName: "standard"
    accessModes:
      - ReadWriteOnce
    resources:
      requests:
        storage: 1Gi
  init:
    scriptSource:
      configMap:
        name: mg-init-script
  backupSchedule:
    cronExpression: "@every 2m"
    storageSecretName: mg-snap-secret
    gcs:
      bucket: kubedb-qa
      prefix: demo
  monitor:
    agent: prometheus.io/operator
    prometheus:
      serviceMonitor:
        labels:
          app: kubedb
        interval: 10s
  configSecret:
    name: mg-custom-config
  podTemplate:
    annotations:
      passMe: ToDatabasePod
    controller:
      annotations:
        passMe: ToStatefulSet
    spec:
      serviceAccountName: my-service-account
      schedulerName: my-scheduler
      nodeSelector:
        disktype: ssd
      imagePullSecrets:
        - name: myregistrykey
      args:
        - --maxConns=100
      env:
        - name: MONGO_INITDB_DATABASE
          value: myDB
      resources:
        requests:
          memory: "64Mi"
          cpu: "250m"
        limits:
          memory: "128Mi"
          cpu: "500m"
  serviceTemplate:
    annotations:
      passMe: ToService
    spec:
      type: NodePort
      ports:
        - name: http
          port: 9200
          targetPort: http
  terminationPolicy: Halt

spec.version

spec.version is a required field specifying the name of the MongoDBVersion crd where the docker images are specified. Currently, when you install KubeDB, it creates the following MongoDBVersion resources,

  • 3.4-v5, 3.4-v4, 3.4-v3, 3.4-v2, 3.4-v1, 3.4
  • 3.6-v5, 3.6-v4, 3.6-v3, 3.6-v2, 3.6-v1, 3.6
  • 4.0.5-v3, 4.0.5-v2, 4.0.5-v1, 4.0-v1, 4.0.5, 4.0
  • 4.1.4-v1, 4.1.4
  • 4.1.7-v3, 4.1.7-v2, 4.1.7-v1, 4.1.7
  • 4.1.13-v1, 4.1.13
  • 4.2,
  • 4.2.3,
  • 3.6.18-percona, 4.0.10-percona, 4.2.7-percona

spec.replicas

spec.replicas the number of members in rs0 mongodb replicaset.

If spec.shardTopology is set, then spec.replicas needs to be empty. Instead use spec.shardTopology.<shard/configServer>.replicas

If both spec.replicaset and spec.shardTopology is not set, then spec.replicas can be value 1.

KubeDB uses PodDisruptionBudget to ensure that majority of these replicas are available during voluntary disruptions so that quorum is maintained.

spec.authSecret

spec.authSecret is an optional field that points to a Secret used to hold credentials for mongodb superuser. 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.authSecret.name.

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

Example:

$ kubectl create secret generic mgo1-auth -n demo \
--from-literal=username=jhon-doe \
--from-literal=password=6q8u_2jMOW-OOZXk
secret "mgo1-auth" created
apiVersion: v1
data:
  password: NnE4dV8yak1PVy1PT1pYaw==
  username: amhvbi1kb2U=
kind: Secret
metadata:
  ...
  name: mgo1-auth
  namespace: demo
  ...
type: Opaque

Secrets provided by users are not managed by KubeDB, and therefore, won’t be modified or garbage collected by the KubeDB operator (version 0.13.0 and higher).

spec.replicaSet

spec.replicaSet represents the configuration for replicaset. When spec.replicaSet is set, KubeDB will deploy a mongodb replicaset where number of replicaset member is spec.replicas.

  • name denotes the name of mongodb replicaset.

  • keyFileSecret is deprecated now. Use spec.certificateSecret instead. For existing MongoDB instances, KubeDB operator will handle the migration by itself. keyFileSecret field will be removed in future.

NB. If spec.shardTopology is set, then spec.replicaset needs to be empty.

spec.shardTopology

spec.shardTopology represents the topology configuration for sharding.

Available configurable fields:

  • shard
  • configServer
  • mongos

When spec.shardTopology is set, the following fields needs to be empty, otherwise validating webhook will throw error.

  • spec.replicas
  • spec.podTemplate
  • spec.configSecret
  • spec.storage

KubeDB uses PodDisruptionBudget to ensure that majority of the replicas of these shard components are available during voluntary disruptions so that quorum and data integrity is maintained.

spec.shardTopology.shard

shard represents configuration for Shard component of mongodb.

Available configurable fields:

  • 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.
  • configSource 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. See below to know about spec.configSecret in details.
  • podTemplate is an optional configuration for pods. See below to know about spec.podTemplate in details.
  • storage to specify pvc spec for each node of sharding. You can specify any StorageClass available in your cluster with appropriate resource requests. See below to know about spec.storage in details.

spec.shardTopology.configServer

configServer represents configuration for ConfigServer component of mongodb.

Available configurable fields:

  • replicas represents number of replicas for configServer replicaset. Here, configServer is deployed as a replicaset of mongodb.
  • prefix represents the prefix of configServer nodes.
  • configSource 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. See below to know about spec.configSecret in details.
  • podTemplate is an optional configuration for pods. See below to know about spec.podTemplate in details.
  • storage to specify pvc spec for each node of configServer. You can specify any StorageClass available in your cluster with appropriate resource requests. See below to know about spec.storage in details.

spec.shardTopology.mongos

mongos represents configuration for Mongos component of mongodb.

Available configurable fields:

  • replicas represents number of replicas of Mongos instance. Here, Mongos is deployed as stateless (deployment) instance.
  • prefix represents the prefix of mongos nodes.
  • configSource 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. See below to know about spec.configSecret in details.
  • podTemplate is an optional configuration for pods. See below to know about spec.podTemplate in details.
  • strategy is the deployment strategy to use to replace existing pods with new ones. This is optional. If not provided, kubernetes will use default deploymentStrategy, ie. RollingUpdate. See more about Deployment Strategy.

spec.sslMode

Enables TLS/SSL or mixed TLS/SSL used for all network connections. The value of sslMode field can be one of the following:

ValueDescription
disabledThe server does not use TLS/SSL.
allowSSLConnections between servers do not use TLS/SSL. For incoming connections, the server accepts both TLS/SSL and non-TLS/non-SSL.
preferSSLConnections between servers use TLS/SSL. For incoming connections, the server accepts both TLS/SSL and non-TLS/non-SSL.
requireSSLThe server uses and accepts only TLS/SSL encrypted connections.

spec.tls

spec.tls specifies the TLS/SSL configurations for the MongoDB. KubeDB uses cert-manager v1 api to provision and manage TLS certificates.

The following fields are configurable in the spec.tls section:

  • issuerRef is a reference to the Issuer or ClusterIssuer CR of cert-manager that will be used by KubeDB to generate necessary certificates.

    • apiGroup is the group name of the resource that is being referenced. Currently the only supported value is cert-manager.io.
    • kind is the type of resource that is being referenced. KubeDB supports both Issuer and ClusterIssuer as values for this field.
    • name is the name of the resource (Issuer or ClusterIssuer) being referenced.
  • certificates (optional) are a list of certificates used to configure the server and/or client certificate. It has the following fields:

    • alias represents the identifier of the certificate. It has the following possible value:
      • server is used for server certificate identification.
      • client is used for client certificate identification.
      • metrics-exporter is used for metrics exporter certificate identification.
    • secretName (optional) specifies the k8s secret name that holds the certificates.

      This field is optional. If the user does not specify this field, the default secret name will be created in the following format: <database-name>-<cert-alias>-cert.

    • subject (optional) specifies an X.509 distinguished name. It has the following possible field,
      • organizations (optional) are the list of different organization names to be used on the Certificate.
      • organizationalUnits (optional) are the list of different organization unit name to be used on the Certificate.
      • countries (optional) are the list of country names to be used on the Certificate.
      • localities (optional) are the list of locality names to be used on the Certificate.
      • provinces (optional) are the list of province names to be used on the Certificate.
      • streetAddresses (optional) are the list of a street address to be used on the Certificate.
      • postalCodes (optional) are the list of postal code to be used on the Certificate.
      • serialNumber (optional) is a serial number to be used on the Certificate. You can found more details from Here
    • duration (optional) is the period during which the certificate is valid.
    • renewBefore (optional) is a specifiable time before expiration duration.
    • dnsNames (optional) is a list of subject alt names to be used in the Certificate.
    • ipAddresses (optional) is a list of IP addresses to be used in the Certificate.
    • uris (optional) is a list of URI Subject Alternative Names to be set in the Certificate.
    • emailAddresses (optional) is a list of email Subject Alternative Names to be set in the Certificate.
    • privateKey (optional) specifies options to control private keys used for the Certificate.
      • encoding (optional) is the private key cryptography standards (PKCS) encoding for this certificate’s private key to be encoded in. If provided, allowed values are “pkcs1” and “pkcs8” standing for PKCS#1 and PKCS#8, respectively. It defaults to PKCS#1 if not specified.

spec.clusterAuthMode

The authentication mode used for cluster authentication. This option can have one of the following values:

ValueDescription
keyFileUse a keyfile for authentication. Accept only keyfiles.
sendKeyFileFor rolling upgrade purposes. Send a keyfile for authentication but can accept both keyfiles and x.509 certificates.
sendX509For rolling upgrade purposes. Send the x.509 certificate for authentication but can accept both keyfiles and x.509 certificates.
x509Recommended. Send the x.509 certificate for authentication and accept only x.509 certificates.

spec.storageType

spec.storageType is an optional field that specifies the type of storage to use for database. It can be either Durable or Ephemeral. The default value of this field is Durable. If Ephemeral is used then KubeDB will create MongoDB database using emptyDir volume. In this case, you don’t have to specify spec.storage field.

spec.storage

Since 0.9.0-rc.0, If you set spec.storageType: to Durable, then spec.storage is a required 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.

  • 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:

NB. If spec.shardTopology is set, then spec.storage needs to be empty. Instead use spec.shardTopology.<shard/configServer>.storage

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:

  1. Initialize from Script
  2. Initialize from Snapshot

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 script from a configMap can be used to initialize a MongoDB database.

apiVersion: kubedb.com/v1alpha2
kind: MongoDB
metadata:
  name: mgo1
spec:
  version: 3.4-v2
  init:
    scriptSource:
      configMap:
        name: mongodb-init-script

In the above example, KubeDB operator will launch a Job to execute all js script of mongodb-init-script in alphabetical order once StatefulSet pods are running. For more details tutorial on how to initialize from script, please visit here.

spec.monitor

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

spec.configSecret

spec.configSecret is an optional field that allows users to provide custom configuration for MongoDB. This field accepts a VolumeSource. You can use any kubernetes supported volume source such as configMap, secret, azureDisk etc.

Please note that, the configfile name needs to be mongod.conf for mongodb.

To learn more about how to use a custom configuration file see here.

NB. If spec.shardTopology is set, then spec.configsource needs to be empty. Instead use spec.shardTopology.<shard/configServer/mongos>.configSource

spec.podTemplate

KubeDB allows providing a template for database pod through spec.podTemplate. KubeDB operator will pass the information provided in spec.podTemplate to the StatefulSet created for MongoDB database.

KubeDB accept following fields to set in spec.podTemplate:

  • metadata:
    • annotations (pod’s annotation)
  • controller:
    • annotations (statefulset’s annotation)
  • spec:
    • args
    • env
    • resources
    • initContainers
    • imagePullSecrets
    • nodeSelector
    • affinity
    • serviceAccountName
    • schedulerName
    • tolerations
    • priorityClassName
    • priority
    • securityContext
    • livenessProbe
    • readinessProbe
    • lifecycle

Uses of some field of spec.podTemplate is described below,

NB. If spec.shardTopology is set, then spec.podTemplate needs to be empty. Instead use spec.shardTopology.<shard/configServer/mongos>.podTemplate

spec.podTemplate.spec.args

spec.podTemplate.spec.args is an optional field. This can be used to provide additional arguments to database installation. To learn about available args of mongod, visit here.

spec.podTemplate.spec.env

spec.podTemplate.spec.env is an optional field that specifies the environment variables to pass to the MongoDB docker image. To know about supported environment variables, please visit here.

Note that, KubeDB does not allow MONGO_INITDB_ROOT_USERNAME and MONGO_INITDB_ROOT_PASSWORD environment variables to set in spec.podTemplate.spec.env. If you want to use custom superuser and password, please use spec.authSecret instead described earlier.

If you try to set MONGO_INITDB_ROOT_USERNAME or MONGO_INITDB_ROOT_PASSWORD environment variable in MongoDB crd, Kubed operator will reject the request with following error,

Error from server (Forbidden): error when creating "./mongodb.yaml": admission webhook "mongodb.validators.kubedb.com" denied the request: environment variable MONGO_INITDB_ROOT_USERNAME is forbidden to use in MongoDB spec

Also, note that KubeDB does not allow updating the environment variables as updating them does not have any effect once the database is created. If you try to update environment variables, KubeDB operator will reject the request with following error,

Error from server (BadRequest): error when applying patch:
...
for: "./mongodb.yaml": admission webhook "mongodb.validators.kubedb.com" denied the request: precondition failed for:
...At least one of the following was changed:
    apiVersion
    kind
    name
    namespace
    spec.ReplicaSet
    spec.authSecret
    spec.init
    spec.storageType
    spec.storage
    spec.podTemplate.spec.nodeSelector
    spec.podTemplate.spec.env

spec.podTemplate.spec.imagePullSecret

KubeDB provides the flexibility of deploying MongoDB database from a private Docker registry. spec.podTemplate.spec.imagePullSecrets is an optional field that points to secrets to be used for pulling docker image if you are using a private docker registry. To learn how to deploy MongoDB from a private registry, please visit here.

spec.podTemplate.spec.nodeSelector

spec.podTemplate.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.podTemplate.spec.serviceAccountName

serviceAccountName is an optional field supported by KubeDB Operator (version 0.13.0 and higher) that can be used to specify a custom service account to fine tune role based access control.

If this field is left empty, the KubeDB operator will create a service account name matching MongoDB crd name. Role and RoleBinding that provide necessary access permissions will also be generated automatically for this service account.

If a service account name is given, but there’s no existing service account by that name, the KubeDB operator will create one, and Role and RoleBinding that provide necessary access permissions will also be generated for this service account.

If a service account name is given, and there’s an existing service account by that name, the KubeDB operator will use that existing service account. Since this service account is not managed by KubeDB, users are responsible for providing necessary access permissions manually. Follow the guide here to grant necessary permissions in this scenario.

spec.podTemplate.spec.resources

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

spec.serviceTemplate

You can also provide a template for the services created by KubeDB operator for MongoDB database through spec.serviceTemplate. This will allow you to set the type and other properties of the services.

KubeDB allows following fields to set in spec.serviceTemplate:

  • metadata:
    • annotations
  • spec:
    • type
    • ports
    • clusterIP
    • externalIPs
    • loadBalancerIP
    • loadBalancerSourceRanges
    • externalTrafficPolicy
    • healthCheckNodePort
    • sessionAffinityConfig

See here to understand these fields in detail.

spec.terminationPolicy

terminationPolicy gives flexibility whether to nullify(reject) the delete operation of MongoDB crd or which resources KubeDB should keep or delete when you delete MongoDB crd. KubeDB provides following four termination policies:

  • DoNotTerminate
  • Halt
  • Delete (Default)
  • WipeOut

When terminationPolicy is DoNotTerminate, KubeDB takes advantage of ValidationWebhook feature in Kubernetes 1.9.0 or later clusters to implement DoNotTerminate feature. If admission webhook is enabled, DoNotTerminate prevents users from deleting the database as long as the spec.terminationPolicy is set to DoNotTerminate.

Following table show what KubeDB does when you delete MongoDB crd for different termination policies,

BehaviorDoNotTerminateHaltDeleteWipeOut
1. Block Delete operation
2. Create Dormant Database
3. Delete StatefulSet
4. Delete Services
5. Delete PVCs
6. Delete Secrets
7. Delete Snapshots
8. Delete Snapshot data from bucket

If you don’t specify spec.terminationPolicy KubeDB uses Halt termination policy by default.

Next Steps