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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-v2"
replicas: 2
standbyMode: Hot
streamingMode: asynchronous
leaderElection:
leaseDurationSeconds: 15
renewDeadlineSeconds: 10
retryPeriodSeconds: 2
archiver:
storage:
storageSecretName: s3-secret
s3:
bucket: kubedb
databaseSecret:
secretName: p1-auth
storageType: "Durable"
storage:
storageClassName: standard
accessModes:
- ReadWriteOnce
resources:
requests:
storage: 1Gi
init:
scriptSource:
configMap:
name: pg-init-script
backupSchedule:
cronExpression: "@every 2m"
storageSecretName: gcs-secret
gcs:
bucket: kubedb-qa
prefix: demo
monitor:
agent: prometheus.io/coreos-operator
prometheus:
namespace: demo
labels:
app: kubedb
interval: 10s
configSource:
configMap:
name: pg-custom-config
podTemplate:
metadata:
annotations:
passMe: ToDatabasePod
controller:
annotations:
passMe: ToStatefulSet
spec:
schedulerName: my-scheduler
nodeSelector:
disktype: ssd
imagePullSecrets:
- name: myregistrykey
env:
- name: POSTGRES_DB
value: pgdb
resources:
requests:
memory: "64Mi"
cpu: "250m"
limits:
memory: "128Mi"
cpu: "500m"
serviceTemplate:
metadata:
annotations:
passMe: ToService
spec:
type: NodePort
ports:
- name: http
port: 5432
targetPort: http
replicaServiceTemplate:
annotations:
passMe: ToReplicaService
spec:
type: NodePort
ports:
- name: http
port: 5432
targetPort: http
updateStrategy:
type: RollingUpdate
terminationPolicy: "Pause"
spec.version
spec.version
is a required field that specifies the name of the PostgresVersion crd where the docker images are specified. Currently, when you install KubeDB, it creates the following PostgresVersion
crd,
9.6.7-v2
,9.6.7-v1
,9.6.7
,9.6-v2
,9.6
10.2-v2
,10.2-v1
,10.2
10.6
11.1
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. To know more about how to setup a HA PostgreSQL cluster in KubeDB, please visit here.
spec.standbyMode
spec.standby
is an optional field that specifies the standby mode (Warm / Hot) to use for standby replicas. In hot standby mode, standby replicas can accept connection and run read-only queries. In warm standby mode, standby replicas can’t accept connection and only used for replication purpose.
spec.streamingMode
spec.streamingMode
is an optional field that specifies the streaming mode (synchronous / asynchronous) of the standby replicas. KubeDB currently supports only asynchronous streaming mode.
spec.leaderElection
There are three fields under Postgres CRD’s spec.leaderElection
. These values defines how fast the leader election can happen.
leaseDurationSeconds
: This is the duration in seconds that non-leader candidates will wait to force acquire leadership. This is measured against time of last observed ack. Default 15 sec.renewDeadlineSeconds
: This is the duration in seconds that the acting master will retry refreshing leadership before giving up. Normally, LeaseDuration * 2 / 3. Default 10 sec.retryPeriodSeconds
: This is the duration in seconds the LeaderElector clients should wait between tries of actions. Normally, LeaseDuration / 3. Default 2 sec.
If the Cluster machine is powerful, user can reduce the times. But, Do not make it so little, in that case Postgres will restarts very often.
spec.archiver
spec.archiver
is an optional field which specifies storage information that will be used by wal-g
. User can use either s3 or gcs.
storage.storageSecretName
points to the Secret containing the credentials for cloud storage destination.storage.s3
points to s3 storage configuration.storage.s3.bucket
points to the bucket name used to store continuous archiving data.storage.gcs
points to GCS storage configuration.storage.gcs.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/
.
Follow this link to learn how to create secret for S3 or GCS. To know more about how to configure Postgres to archive WAL data continuously in AWS S3 bucket, please visit here.
spec.databaseSecret
spec.databaseSecret
is an optional field that points to a Secret used to hold credentials for postgres
database. If not set, KubeDB operator creates a new Secret with name {postgres-name}-auth
that hold username and password for postgres
database.
If you want to use an existing or custom secret, please specify that when creating the Postgres object using spec.databaseSecret.secretName
. This Secret should contain superuser username as POSTGRES_USER
key and superuser password as POSTGRES_PASSWORD
key.
Example:
$ kubectl create secret generic p1-auth -n demo \
--from-literal=POSTGRES_USER=not@user \
--from-literal=POSTGRES_PASSWORD=not@secret
secret "p1-auth" created
$ kubectl get secret -n demo p1-auth -o yaml
apiVersion: v1
data:
POSTGRES_PASSWORD: bm90QHNlY3JldA==
POSTGRES_USER: bm90QHVzZXI=
kind: Secret
metadata:
creationTimestamp: 2018-09-03T11:25:39Z
name: p1-auth
namespace: demo
resourceVersion: "1677"
selfLink: /api/v1/namespaces/demo/secrets/p1-auth
uid: 15b3e8a1-af6c-11e8-996d-0800270d7bae
type: Opaque
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 Postgres database using emptyDir volume. In this case, you don’t have to specify spec.storage
field.
spec.storage
If you don’t set spec.storageType:
to Ephemeral
then spec.storage
field is required. This field 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:
spec.init
spec.init
is an optional section that can be used to initialize a newly created Postgres database. PostgreSQL databases can be initialized from these three ways:
- Initialize from Script
- Initialize from Snapshot
- Initialize from WAL archive
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 the following information:
- VolumeSource: Where your script is loaded from.
Below is an example showing how a script from a configMap can be used to initialize a PostgreSQL database.
apiVersion: kubedb.com/v1alpha1
kind: Postgres
metadata:
name: postgres-db
spec:
version: "9.6-v2"
init:
scriptSource:
configMap:
name: pg-init-script
In the above example, Postgres will execute provided script once the database is running. For more details tutorial on how to initialize from script, please visit here.
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 the following information:
name:
Name of the Snapshotnamespace:
Namespace of the Snapshot
apiVersion: kubedb.com/v1alpha1
kind: Postgres
metadata:
name: postgres-db
spec:
version: "9.6-v2"
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
of demo
namespace. Here, KubeDB operator will launch a Job to initialize PostgreSQL once StatefulSet pods are running.
When initializing from Snapshot, superuser credentials must have to match with the previous one. For example, let’s say, Snapshot snapshot-xyz
is for Postgres postgres-old
. In this case, new Postgres postgres-db
should use the same credentials for superuser of postgres-old
. Otherwise, the restoration process will fail.
For more details tutorial on how to initialize from snapshot, please visit here.
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-v2"
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 credentials must have to match with the previous one. For example, let’s say, we want to initialize this database from postgres-old
WAL archive. In this case, superuser credentials of new Postgres should be the same as postgres-old
. Otherwise, the restoration process will be failed.
For more details tutorial on how to initialize from wal archive, please visit here.
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.
You have to specify following fields to take periodic backup of your Postgres database:
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.
You can also specify a template for pod of backup job through spec.backupSchedule.podTemplate
. KubeDB will use the information you have provided in podTemplate
to create the backup job. KubeDB accept following fields to set in spec.backupSchedule.podTemplate
:
- metadata
- annotations (pod’s annotation)
- controller
- annotations (job’s annotation)
- spec:
- args
- env
- resources
- imagePullSecrets
- initContainers
- nodeSelector
- affinity
- schedulerName
- tolerations
- priorityClassName
- priority
- securityContext
- livenessProbe
- readinessProbe
- lifecycle
spec.monitor
PostgreSQL managed by KubeDB can be monitored with builtin-Prometheus and CoreOS-Prometheus operator out-of-the-box. To learn more,
spec.configSource
spec.configSource
is an optional field that allows users to provide custom configuration for PostgreSQL. This field accepts a VolumeSource
. You can use any kubernetes supported volume source such as configMap
, secret
, azureDisk
etc. To learn more about how to use a custom configuration file see here.
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 Postgres database.
KubeDB accept following fields to set in spec.podTemplate:
- metadata
- annotations (pod’s annotation)
- controller
- annotations (statefulset’s annotation)
- spec:
- env
- resources
- initContainers
- imagePullSecrets
- nodeSelector
- affinity
- schedulerName
- tolerations
- priorityClassName
- priority
- securityContext
- livenessProbe
- readinessProbe
- lifecycle
Uses of some field of spec.podTemplate
is described below,
spec.podTemplate.spec.env
spec.podTemplate.spec.env
is an optional field that specifies the environment variables to pass to the Postgres docker image. To know about supported environment variables, please visit here.
Note that, KubeDB does not allow POSTGRES_USER
and POSTGRES_PASSWORD
environment variable to set in spec.podTemplate.spec.env
. If you want to set the superuser username and password, please use spec.databaseSecret
instead described earlier.
If you try to set POSTGRES_USER
or POSTGRES_PASSWORD
environment variable in Postgres crd, KubeDB operator will reject the request with following error,
Error from server (Forbidden): error when creating "./postgres.yaml": admission webhook "postgres.validators.kubedb.com" denied the request: environment variable POSTGRES_PASSWORD is forbidden to use in Postgres spec
Also, note that KubeDB does not allow to update 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: "./postgres.yaml": admission webhook "postgres.validators.kubedb.com" denied the request: precondition failed for:
...
At least one of the following was changed:
apiVersion
kind
name
namespace
spec.standby
spec.streaming
spec.archiver
spec.databaseSecret
spec.storageType
spec.storage
spec.podTemplate.spec.nodeSelector
spec.init
spec.podTemplate.spec.imagePullSecrets
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. For more details on how to use private docker 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.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
KubeDB creates two different services for each Postgres instance. One of them is a master service named <postgres-name>
and points to the Postgres Primary
pod/node. Another one is a replica service named <postgres-name>-replicas
and points to Postgres replica
pods/nodes.
These master
and replica
services can be customized using spec.serviceTemplate and spec.replicaServiceTemplate respectively.
You can provide template for the master
service using spec.serviceTemplate
. This will allow you to set the type and other properties of the service. If spec.serviceTemplate
is not provided, KubeDB will create a master
service of type ClusterIP
with minimal settings.
KubeDB allows following fields to set in spec.serviceTemplate
:
- metadata:
- annotations
- spec:
- type
- ports
- clusterIP
- externalIPs
- loadBalancerIP
- loadBalancerSourceRanges
- externalTrafficPolicy
- healthCheckNodePort
See official v1.13 API documentation to understand these fields in detail.
spec.replicaServiceTemplate
You can provide template for the replica
service using spec.replicaServiceTemplate
. If spec.replicaServiceTemplate
is not provided, KubeDB will create a replica
service of type ClusterIP
with minimal settings.
The fileds of spec.replicaServiceTemplate
is similar to spec.serviceTemplate
, that is:
- metadata:
- annotations
- spec:
- type
- ports
- clusterIP
- externalIPs
- loadBalancerIP
- loadBalancerSourceRanges
- externalTrafficPolicy
- healthCheckNodePort
See official v1.13 API documentation to understand these fields in detail.
spec.updateStrategy
You can specify update strategy of StatefulSet created by KubeDB for Postgres database thorough spec.updateStrategy
field. The default value of this field is RollingUpdate
. In future, we will use this field to determine how automatic migration from old KubeDB version to new one should behave.
spec.terminationPolicy
terminationPolicy
gives flexibility whether to nullify
(reject) the delete operation of Postgres
crd or which resources KubeDB should keep or delete when you delete Postgres
crd. KubeDB provides following four termination policies:
- DoNotTerminate
- Pause (
Default
) - Delete
- WipeOut
When, terminationPolicy
is DoNotTerminate
, KubeDB takes advantage of ValidationWebhook
feature in Kubernetes 1.9.0 or later clusters to provide safety from accidental deletion of database. If admission webhook is enabled, KubeDB 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 Postgres crd for different termination policies,
Behaviour | DoNotTerminate | Pause | Delete | WipeOut |
---|---|---|---|---|
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 | ✗ | ✗ | ✗ | ✓ |
9. Delete archieved WAL data from bucket | ✗ | ✗ | ✗ | ✓ |
If you don’t specify spec.terminationPolicy
KubeDB uses Pause
termination policy by default.
Next Steps
- Learn how to use KubeDB to run a PostgreSQL database here.
- See the list of supported storage providers for snapshots here.
- Want to hack on KubeDB? Check our contribution guidelines.