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Postgres

What is Postgres

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

Postgres Spec

As with all other Kubernetes objects, a Postgres needs apiVersion, kind, and metadata fields. It also needs a .spec section.

Below is an example Postgres object.

apiVersion: kubedb.com/v1alpha1
kind: Postgres
metadata:
  name: p1
  namespace: demo
spec:
  version: 9.6
  replicas: 2
  standbyMode: hot
  archiver:
    storage:
      storageSecretName: s3-secret
      s3:
        bucket: kubedb
  databaseSecret:
    secretName: p1-auth
  storage:
    storageClassName: standard
    accessModes:
    - ReadWriteOnce
    resources:
      requests:
        storage: 50Mi
  nodeSelector:
    disktype: ssd
  init:
    scriptSource:
      gitRepo:
        directory: "."
        repository: "https://github.com/kubedb/postgres-init-scripts.git"
  backupSchedule:
    cronExpression: "@every 6h"
    storageSecretName: gcs-secret
    gcs:
      bucket: kubedb
      prefix: demo
  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 PostgreSQL database. Currently the supported versions are:

  • 9.6.7, 9.6
  • 10.2

spec.replicas

spec.replicas specifies the total number of primary and standby nodes in Postgres database cluster configuration. One pod is selected as Primary and others are acted as standby replicas.

spec.standby

spec.standby is an optional field that specifies standby mode (warm/hot) supported by Postgres. Hot standby can run read-only queries where Warm standby can’t accept connect and only used for replication purpose.

spec.archiver

spec.archiver is an optional field which specifies storage information that will be used by wal-g.

  • spec.archiver.storage.storageSecretName points to the Secret containing the credentials for cloud storage destination.
  • spec.archiver.storage.s3.bucket points to the bucket name used to store continuous archiving data.

Continuous archiving data will be stored in a folder called {bucket}/{prefix}/kubedb/{namespace}/{postgres-name}/archive/.

spec.databaseSecret

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

This Secret contains postgres superuser password as POSTGRES_PASSWORD key.

spec.storage

Since 0.8.0-rc.0, 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: - https://kubernetes.io/docs/concepts/storage/persistent-volumes/#persistentvolumeclaims

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 Postgres database. PostgreSQL databases can be initialized in one of three ways:

Initialize via Script

To initialize a PostgreSQL database using a script (shell script, db migrator, etc.), set the spec.init.scriptSource section when creating a Postgres object. ScriptSource must have following information:

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

apiVersion: kubedb.com/v1alpha1
kind: Postgres
metadata:
  name: postgres-db
spec:
  version: 9.6
  init:
    scriptSource:
      gitRepo:
        directory: "."
        repository: "https://github.com/kubedb/postgres-init-scripts.git"

In the above example, Postgres will execute provided script once database is running. directory: . is used to get repository contents directly in mount path.

Initialize from Snapshots

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

  • name: Name of the Snapshot
  • namespace: Namespace of the Snapshot
apiVersion: kubedb.com/v1alpha1
kind: Postgres
metadata:
  name: postgres-db
spec:
  version: 9.6
  databaseSecret:
    secretName: postgres-old-auth
  init:
    snapshotSource:
      name: "snapshot-xyz"
      namespace: "demo"

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

When initializing from Snapshot, superuser postgres must have to match with previous one. For example, lets say, Snapshot snapshot-xyz is for Postgres postgres-old. In this case, new Postgres postgres-db should use same credential for superuser of postgres-old. Otherwise, restoration process will fail.

Initialize from WAL archive

To initialize from WAL archive, set the spec.init.postgresWAL section when creating a Postgres object.

Below is an example showing how to initialize a PostgreSQL database from WAL archive.

apiVersion: kubedb.com/v1alpha1
kind: Postgres
metadata:
  name: postgres-db
spec:
  version: 9.6
  databaseSecret:
    secretName: postgres-old
  init:
    postgresWAL:
      storageSecretName: s3-secret
      s3:
        endpoint: 's3.amazonaws.com'
        bucket: kubedb
        prefix: 'kubedb/demo/old-pg/archive'

In the above example, PostgreSQL database will be initialized from WAL archive.

When initializing from WAL archive, superuser postgres must have to match with previous one. For example, lets say, we want to initialize this database from postgres-old WAL archive. In this case, superuser of new Postgres should use same password as postgres-old. Otherwise, restoration process will be failed.

spec.backupSchedule

KubeDB supports taking periodic snapshots for Postgres 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

KubeDB takes advantage of ValidationWebhook feature in Kubernetes 1.9.0 or later clusters to implement doNotPause feature. If admission webhook is enabled, It prevents user from deleting the database as long as the spec.doNotPause is set true. If not set or set to false, deleting a Postgres 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.monitor

PostgreSQL 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 PostgreSQL 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.

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