administrator.md

Create ConfigMap

A ConfigMap is used to store the configuration of the operator.

    $ kubectl create -f manifests/configmap.yaml

Deploying the operator

First you need to install the service account definition in your Minikube cluster.

    $ kubectl create -f manifests/operator-service-account-rbac.yaml

Next deploy the postgres-operator from the docker image Zalando is using:

    $ kubectl create -f manifests/postgres-operator.yaml

If you prefer to build the image yourself follow up down below.

Check if CustomResourceDefinition has been registered

    $ kubectl get crd

	NAME                          KIND
	postgresqls.acid.zalan.do     CustomResourceDefinition.v1beta1.apiextensions.k8s.io

How to configure PostgreSQL operator

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 $(kubectl config current-context) --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 ConfigMap - there. Please note that the namespace for service accounts and cluster role bindings in operator RBAC rules needs to be adjusted to the non-default value.

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 setting the WATCHED_NAMESPACE var in the env section of the operator deployment manifest or by altering 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-service-account-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-service-account-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 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 resources), 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"
  ...

Note that the Kubernetes version 1.13 brings taint-based eviction to the beta stage and enables it by default. Postgres pods by default receive tolerations for unreachable and noExecute taints with the timeout of 5m. Depending on your setup, you may want to adjust these parameters to prevent master pods from being evicted by the Kubernetes runtime. To prevent eviction completely, specify the toleration by leaving out the tolerationSeconds value (similar to how Kubernetes' own DaemonSets are configured)

Add cluster-specific labels

In some cases, you might want to add labels that are specific to a given postgres cluster, in order to identify its child objects. The typical use case is to add labels that identifies the Pods created by the operator, in order to implement fine-controlled NetworkPolicies.

OperatorConfiguration

apiVersion: "acid.zalan.do/v1"
kind: OperatorConfiguration
metadata:
  name: postgresql-operator-configuration
configuration:
  kubernetes:
    inherited_labels:
    - application
    - environment
...

cluster manifest

apiVersion: "acid.zalan.do/v1"
kind: postgresql
metadata:
  name: demo-cluster
  labels:
    application: my-app
    environment: demo
spec:
...

network policy

kind: NetworkPolicy
apiVersion: networking.k8s.io/v1
metadata:
  name: netpol-example
spec:
  podSelector:
    matchLabels:
      application: my-app
      environment: demo
...

Custom Pod Environment Variables

It is possible to configure a ConfigMap 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 ConfigMap with the additional settings is configured in the operator's main ConfigMap:

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.

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 Kubernetes 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 all namespaces watched by the operator.

To limit the range of IP adresses that can reach a load balancer, specify the desired ranges in the allowedSourceRanges field (applies to both master and replica load balancers). To prevent exposing load balancers to the entire Internet, this field is set at cluster creation time to 127.0.0.1/32 unless overwritten explicitly. If you want to revoke all IP ranges from an existing cluster, please set the allowedSourceRanges field to 127.0.0.1/32 or to an empty sequence []. Setting the field to null or omitting it entirely may lead to Kubernetes removing this field from the manifest due to its handling of null fields. Then the resultant manifest will not contain the necessary change, and the operator will respectively do noting with the existing source ranges.

Running periodic 'autorepair' scans of Kubernetes objects

The Postgres operator periodically scans all Kubernetes objects belonging to each cluster and repairs all discrepancies between them and the definitions generated from the current cluster manifest. There are two types of scans:

• sync scan, running every resync_period seconds for every cluster

• repair scan, coming every repair_period only for those clusters that didn't report success as a result of the last operation applied to them.

Postgres roles supported by the operator

The operator is capable of maintaining roles of multiple kinds within a Postgres database cluster:

• System roles are roles necessary for the proper work of Postgres itself such as a replication role or the initial superuser role. The operator delegates creating such roles to Patroni and only establishes relevant secrets.

• Infrastructure roles are roles for processes originating from external systems, e.g. monitoring robots. The operator creates such roles in all Postgres clusters it manages assuming that Kubernetes secrets with the relevant credentials exist beforehand.

• Per-cluster robot users are also roles for processes originating from external systems but defined for an individual Postgres cluster in its manifest. A typical example is a role for connections from an application that uses the database.

• Human users originate from the Teams API that returns a list of the team members given a team id. The operator differentiates between (a) product teams that own a particular Postgres cluster and are granted admin rights to maintain it, and (b) Postgres superuser teams that get the superuser access to all Postgres databases running in a Kubernetes cluster for the purposes of maintaining and troubleshooting.

Understanding rolling update of Spilo pods

The operator logs reasons for a rolling update with the info level and a diff between the old and new StatefulSet specs with the debug level. To read the latter log entry with the escaped characters rendered, view it in CLI with echo -e. Note that the resultant message will contain some noise because the PodTemplate used by the operator is yet to be updated with the default values used internally in Kubernetes.