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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/v1
kind: Postgres
metadata:
name: p1
namespace: demo
spec:
version: "13.13"
replicas: 2
standbyMode: Hot
streamingMode: Asynchronous
leaderElection:
leaseDurationSeconds: 15
renewDeadlineSeconds: 10
retryPeriodSeconds: 2
authSecret:
name: p1-auth
storageType: "Durable"
storage:
storageClassName: standard
accessModes:
- ReadWriteOnce
resources:
requests:
storage: 1Gi
init:
script:
configMap:
name: pg-init-script
monitor:
agent: prometheus.io/operator
prometheus:
serviceMonitor:
labels:
app: kubedb
interval: 10s
configSecret:
name: pg-custom-config
podTemplate:
metadata:
annotations:
passMe: ToDatabasePod
controller:
annotations:
passMe: ToPetSet
spec:
serviceAccountName: my-custom-sa
schedulerName: my-scheduler
nodeSelector:
disktype: ssd
imagePullSecrets:
- name: myregistrykey
containers:
- name: postgres
env:
- name: POSTGRES_DB
value: pgdb
resources:
requests:
memory: "64Mi"
cpu: "250m"
limits:
memory: "128Mi"
cpu: "500m"
serviceTemplates:
- alias: primary
metadata:
annotations:
passMe: ToService
spec:
type: NodePort
ports:
- name: http
port: 5432
- alias: standby
metadata:
annotations:
passMe: ToReplicaService
spec:
type: NodePort
ports:
- name: http
port: 5432
deletionPolicy: "Halt"
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
resources,
$ kubectl get pgversion
NAME VERSION DB_IMAGE DEPRECATED AGE
10.2 10.2 kubedb/postgres:10.2 true 44m
10.2-v1 10.2 kubedb/postgres:10.2-v2 true 44m
10.2-v2 10.2 kubedb/postgres:10.2-v3 44m
10.2-v3 10.2 kubedb/postgres:10.2-v4 44m
10.2-v4 10.2 kubedb/postgres:10.2-v5 44m
10.2-v5 10.2 kubedb/postgres:10.2-v6 44m
10.6 10.6 kubedb/postgres:10.6 44m
10.6-v1 10.6 kubedb/postgres:10.6-v1 44m
10.6-v2 10.6 kubedb/postgres:10.6-v2 44m
10.6-v3 10.6 kubedb/postgres:10.6-v3 44m
11.1 11.1 kubedb/postgres:11.1 44m
11.1-v1 11.1 kubedb/postgres:11.1-v1 44m
11.1-v2 11.1 kubedb/postgres:11.1-v2 44m
11.1-v3 11.1 kubedb/postgres:11.1-v3 44m
11.2 11.2 kubedb/postgres:11.2 44m
11.2-v1 11.2 kubedb/postgres:11.2-v1 44m
9.6 9.6 kubedb/postgres:9.6 true 44m
9.6-v1 9.6 kubedb/postgres:9.6-v2 true 44m
9.6-v2 9.6 kubedb/postgres:9.6-v3 44m
9.6-v3 9.6 kubedb/postgres:9.6-v4 44m
9.6-v4 9.6 kubedb/postgres:9.6-v5 44m
9.6-v5 9.6 kubedb/postgres:9.6-v6 44m
9.6.7 9.6.7 kubedb/postgres:9.6.7 true 44m
9.6.7-v1 9.6.7 kubedb/postgres:9.6.7-v2 true 44m
9.6.7-v2 9.6.7 kubedb/postgres:9.6.7-v3 44m
9.6.7-v3 9.6.7 kubedb/postgres:9.6.7-v4 44m
9.6.7-v4 9.6.7 kubedb/postgres:9.6.7-v5 44m
9.6.7-v5 9.6.7 kubedb/postgres:9.6.7-v6 44m
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 act as standby replicas. KubeDB uses PodDisruptionBudget
to ensure that majority of the replicas are available during voluntary disruptions.
To learn 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.authSecret
spec.authSecret
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.authSecret.name
. This Secret should contain superuser username as POSTGRES_USER
key and superuser password as POSTGRES_PASSWORD
key. 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).
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 PetSet 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 via Script
To initialize a PostgreSQL database using a script (shell script, db migrator, etc.), set the spec.init.script
section when creating a Postgres object. script
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/v1
kind: Postgres
metadata:
name: postgres-db
namespace: demo
spec:
version: "13.13"
init:
script:
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.
spec.monitor
PostgreSQL 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 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 PetSet created for Postgres database.
KubeDB accept following fields to set in spec.podTemplate:
- metadata
- annotations (pod’s annotation)
- controller
- annotations (petset’s annotation)
- spec:
- containers
- volumes
- podPlacementPolicy
- serviceAccountName
- initContainers
- imagePullSecrets
- nodeSelector
- affinity
- schedulerName
- tolerations
- priorityClassName
- priority
- securityContext
- livenessProbe
- readinessProbe
- lifecycle
You can check out the full list here.
Uses of some field of spec.podTemplate
is described below,
spec.podTemplate.spec.tolerations
The spec.podTemplate.spec.tolerations
is an optional field. This can be used to specify the pod’s tolerations.
spec.podTemplate.spec.volumes
The spec.podTemplate.spec.volumes
is an optional field. This can be used to provide the list of volumes that can be mounted by containers belonging to the pod.
spec.podTemplate.spec.podPlacementPolicy
spec.podTemplate.spec.podPlacementPolicy
is an optional field. This can be used to provide the reference of the podPlacementPolicy. This will be used by our Petset controller to place the db pods throughout the region, zone & nodes according to the policy. It utilizes kubernetes affinity & podTopologySpreadContraints feature to do so.
spec.podTemplate.spec.containers
The spec.podTemplate.spec.containers
can be used to provide the list containers and their configurations for to the database pod. some of the fields are described below,
spec.podTemplate.spec.containers[].name
The spec.podTemplate.spec.containers[].name
field used to specify the name of the container specified as a DNS_LABEL. Each container in a pod must have a unique name (DNS_LABEL). Cannot be updated.
spec.podTemplate.spec.containers[].args
spec.podTemplate.spec.containers[].args
is an optional field. This can be used to provide additional arguments to database installation.
spec.podTemplate.spec.containers[].env
spec.podTemplate.spec.containers[].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, the KubeDB operator 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.authSecret
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.authSecret
spec.storageType
spec.storage
spec.podTemplate.spec.nodeSelector
spec.init
spec.podTemplate.spec.containers[].resources
spec.podTemplate.spec.containers[].resources
is an optional field. This can be used to request compute resources required by containers of the database pods. To learn more, visit 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 Postgres 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.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.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
- sessionAffinityConfig
See here 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 here to understand these fields in detail.
spec.deletionPolicy
deletionPolicy
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
- Halt
- Delete (
Default
) - WipeOut
When deletionPolicy
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.deletionPolicy
is set to DoNotTerminate
.
Following table show what KubeDB does when you delete Postgres crd for different termination policies,
Behavior | DoNotTerminate | Halt | Delete | WipeOut |
---|---|---|---|---|
1. Block Delete operation | ✓ | ✗ | ✗ | ✗ |
2. Create Dormant Database | ✗ | ✓ | ✗ | ✗ |
3. Delete PetSet | ✗ | ✓ | ✓ | ✓ |
4. Delete Services | ✗ | ✓ | ✓ | ✓ |
5. Delete PVCs | ✗ | ✗ | ✓ | ✓ |
6. Delete Secrets | ✗ | ✗ | ✗ | ✓ |
7. Delete Snapshots | ✗ | ✗ | ✗ | ✓ |
8. Delete Snapshot data from bucket | ✗ | ✗ | ✗ | ✓ |
If you don’t specify spec.deletionPolicy
KubeDB uses Halt
termination policy by default.
Next Steps
- Learn how to use KubeDB to run a PostgreSQL database here.
- Want to hack on KubeDB? Check our contribution guidelines.