Using Patroni with Kubernetes

Source: https://patroni.readthedocs.io/en/latest/kubernetes.html

Patroni can store cluster state and the leader key in Kubernetes objects. This lets it run Postgres in Kubernetes without a separate consistency store, such as an extra Etcd deployment. Patroni supports two object types for the leader and configuration keys. Select the type with kubernetes.use_endpoints or the PATRONI_KUBERNETES_USE_ENDPOINTS environment variable.

Use Endpoints

This mode is recommended but disabled by default for compatibility. When enabled, Patroni creates Endpoints and stores cluster configuration and the leader key in their metadata: annotations fields. A leader change updates both the leader annotations and the addresses of the leader pod in one operation. This is safer than ConfigMaps.

Use ConfigMaps

In this mode, Patroni creates ConfigMaps and stores keys in their metadata. A leader change needs at least two updates: one for the leader ConfigMap and one for its Endpoint.

To route traffic to the Postgres leader, configure the Kubernetes Postgres service label selector with role_label from the Patroni configuration.

Some environments, such as OpenShift, require ConfigMaps.

Configuration

Patroni Kubernetes settings and environment variables are described in the general chapters of the documentation.

Customize role label

By default, Patroni labels its pod with the node role, such as role=primary. Customize the label key and values with kubernetes.role_label, kubernetes.leader_label_value, kubernetes.follower_label_value, and kubernetes.standby_leader_label_value.

To reduce downtime when you change default role labels to custom labels, use these steps:

1. Set kubernetes.tmp_role_label to a temporary label, such as tmp_role, with the original role value. After the pods restart, Patroni sets these labels:

labels:
  cluster-name: foo
  role: primary
  tmp_role: primary

2. After all pods have been updated, modify the service selector to select the temporary label.

selector:
  cluster-name: foo
  tmp_role: primary

3. Add the custom role label, for example kubernetes.leader_label_value=primary. After the pods restart, Patroni sets these labels:

labels:
  cluster-name: foo
  role: primary
  tmp_role: primary

4. After all pods have been updated again, modify the service selector to use new role value.

selector:
  cluster-name: foo
  role: primary

5. Finally, remove the temporary label from your configuration and update all pods.

labels:
  cluster-name: foo
  role: primary

Examples

• The kubernetes directory contains an example Docker image and Kubernetes manifest for tests. The current example cannot use PersistentVolumes because of permission problems.
• The Spilo Project provides a full-featured Docker image with Persistent Volume support.
• A Helm chart deploys the Spilo image with Patroni configured to run in Kubernetes.
• For Patroni and Spilo clusters at scale, see postgres-operator. It uses the operator pattern to manage Spilo clusters.