postgres-operator/docs/howtos.md

How To

Select the namespace to deploy to

The operator can run in a namespace other than default. For example, to use the test namespace, run the following before deploying the operator's manifests:

kubectl create namespace test kubectl config set-context minikube
--namespace=test

All subsequent kubectl commands will work with the test namespace. The operator will run in this namespace and look up needed resources - such as its config map - there.

Specify the namespace to watch

Watching a namespace for an operator means tracking requests to change Postgresql clusters in the namespace such as "increase the number of Postgresql replicas to 5" and reacting to the requests, in this example by actually scaling up.

By default, the operator watches the namespace it is deployed to. You can change this by altering the WATCHED_NAMESPACE env var in the operator deployment manifest or the watched_namespace field in the operator configmap. In the case both are set, the env var takes the precedence. To make the operator listen to all namespaces, explicitly set the field/env var to "*".

Note that for an operator to manage pods in the watched namespace, the operator's service account (as specified in the operator deployment manifest) has to have appropriate privileges to access the watched namespace. The operator may not be able to function in the case it watches all namespaces but lacks access rights to any of them (except Kubernetes system namespaces like kube-system). The reason is that for multiple namespaces operations such as 'list pods' execute at the cluster scope and fail at the first violation of access rights.

The watched namespace also needs to have a (possibly different) service account in the case database pods need to talk to the Kubernetes API (e.g. when using Kubernetes-native configuration of Patroni). The operator checks that the pod_service_account_name exists in the target namespace, and, if not, deploys there the pod_service_account_definition from the operator Config with the default value of:

apiVersion: v1
kind: ServiceAccount
metadata:
 name: operator

In this definition, the operator overwrites the account's name to match pod_service_account_name and the default namespace to match the target namespace. The operator performs no further syncing of this account.

Role-based access control for the operator

The manifests/operator-rbac.yaml defines cluster roles and bindings needed for the operator to function under access control restrictions. To deploy the operator with this RBAC policy use:

kubectl create -f manifests/configmap.yaml
kubectl create -f manifests/operator-rbac.yaml
kubectl create -f manifests/postgres-operator.yaml
kubectl create -f manifests/minimal-postgres-manifest.yaml

Note that the service account in operator-rbac.yaml is named zalando-postgres-operator. You may have to change the service_account_name in the operator configmap and serviceAccountName in the postgres-operator deployment appropriately.

This is done intentionally, as to avoid breaking those setups that already work with the default operator account. In the future the operator should ideally be run under the zalando-postgres-operator service account.

The service account defined in operator-rbac.yaml acquires some privileges not really used by the operator (i.e. we only need list and watch on configmaps), this is also done intentionally to avoid breaking things if someone decides to configure the same service account in the operator's configmap to run postgres clusters.

Use taints and tolerations for dedicated PostgreSQL nodes

To ensure Postgres pods are running on nodes without any other application pods, you can use taints and tolerations and configure the required toleration in the operator ConfigMap.

As an example you can set following node taint:

$ kubectl taint nodes <nodeName> postgres=:NoSchedule

And configure the toleration for the PostgreSQL pods by adding following line to the ConfigMap:

apiVersion: v1
kind: ConfigMap
metadata:
  name: postgres-operator
data:
  toleration: "key:postgres,operator:Exists,effect:NoSchedule"
  ...

Or you can specify and/or overwrite the tolerations for each PostgreSQL instance in the manifest:

apiVersion: "acid.zalan.do/v1"
kind: postgresql
metadata:
  name: acid-minimal-cluster
spec:
  teamId: "ACID"
  tolerations:
  - key: postgres
    operator: Exists
    effect: NoSchedule

Please be aware that the taint and toleration only ensures that no other pod gets scheduled to a PostgreSQL node but not that PostgreSQL pods are placed on such a node. This can be achieved by setting a node affinity rule in the ConfigMap.

Using the operator to minimize the amount of failovers during the cluster upgrade

Postgres operator moves master pods out of to be decommissioned Kubernetes nodes. The decommission status of the node is derived from the presence of the set of labels defined by the node_readiness_label parameter. The operator makes sure that the Postgres master pods are moved elsewhere from the node that is pending to be decommissioned , but not on another node that is also about to be shut down. It achieves that via a combination of several properties set on the postgres pods:

• nodeAffinity is configured to avoid scheduling the pod on nodes without all labels from the node_readiness_label set.
• PodDisruptionBudget is defined to keep the master pods running until they are moved out by the operator.

The operator starts moving master pods when the node is drained and doesn't have all labels from the node_readiness_label set. By default this parameter is set to an empty string, disabling this feature altogether. It can be set to a string containing one or more key:value parameters, i.e:

node_readiness_label: "lifecycle-status:ready,disagnostic-checks:ok"

when multiple labels are set the operator will require all of them to be present on a node (and set to the specified value) in order to consider it ready.

Custom Pod Environment Variables

It is possible to configure a config map which is used by the Postgres pods as an additional provider for environment variables.

One use case is to customize the Spilo image and configure it with environment variables. The config map with the additional settings is configured in the operator's main config map:

postgres-operator ConfigMap

apiVersion: v1
kind: ConfigMap
metadata:
  name: postgres-operator
data:
  # referencing config map with custom settings
  pod_environment_configmap: postgres-pod-config
  ...

referenced ConfigMap postgres-pod-config

apiVersion: v1
kind: ConfigMap
metadata:
  name: postgres-pod-config
  namespace: default
data:
  MY_CUSTOM_VAR: value

This ConfigMap is then added as a source of environment variables to the Postgres StatefulSet/pods.

❗ Note that there are environment variables defined by the operator itself in order to pass parameters to the Spilo image. The values from the operator for those variables will take precedence over those defined in the pod_environment_configmap.

Limiting the number of instances in clusters with min_instances and max_instances

As a preventive measure, one can restrict the minimum and the maximum number of instances permitted by each Postgres cluster managed by the operator. If either min_instances or max_instances is set to a non-zero value, the operator may adjust the number of instances specified in the cluster manifest to match either the min or the max boundary. For instance, of a cluster manifest has 1 instance and the min_instances is set to 3, the cluster will be created with 3 instances. By default, both parameters are set to -1.

Load balancers

For any Postgresql/Spilo cluster, the operator creates two separate k8s services: one for the master pod and one for replica pods. To expose these services to an outer network, one can attach load balancers to them by setting enableMasterLoadBalancer and/or enableReplicaLoadBalancer to true in the cluster manifest. In the case any of these variables are omitted from the manifest, the operator configmap's settings enable_master_load_balancer and enable_replica_load_balancer apply. Note that the operator settings affect all Postgresql services running in a namespace watched by the operator.