Highly available hosted control planes using external data stores

Setting up a highly available etcd cluster for Kubernetes control planes can be complicated due to their dynamic nature. In k0smotron, we solve this challenge by "externalizing" the HA setup of data storage for the control plane.

The control planes managed by k0smotron are k0s control planes. As k0s comes with support for using SQL databases as data store, which uses Kine, you can use HA databases instead of etcd. This enables you to use, for example, Postgres operator, MySQL operator, or cloud provider managed databases as the data store for the control planes.

Using Postgres operator

This instruction demonstrates how to configure the Postgres operator to manage the data store of a control plane. Use these steps as an example for the required data store resource.

1. Install the Postgres operator following the quickstart guide.

2. Create the database using a custom resource:

   apiVersion: "acid.zalan.do/v1"
   kind: postgresql
   metadata:
     name: acid-minimal-cluster
   spec:
     teamId: "acid"
     volume:
       size: 10Gi
     numberOfInstances: 2
     users:
       # database owner
       k0smotron:
       - superuser
       - createdb
   
     databases:
       kine: k0smotron
     postgresql:
       version: "15"
   

3. Once you set up the database, configure k0smotron to create a control plane:

   cat <<EOF | kubectl apply -f -
   apiVersion: k0smotron.io/v1beta1
   kind: Cluster
   metadata:
     name: k0smotron-test
   spec:
     replicas: 3
     service:
       type: LoadBalancer
     kineDataSourceURL: postgres://k0smotron:<passwd>@acid-minimal-cluster.default:5432/kine?sslmode=disable
   EOF
   

   You can also use the reference to the secret containing the database credentials:

   cat <<EOF | kubectl apply -f -
   apiVersion: v1
   kind: Secret
   metadata:
     name: database-credentials
     namespace: k0smotron-test
   type: Opaque
   data:
     K0SMOTRON_KINE_DATASOURCE_URL: <base64-encoded-datasource>
   ---
   apiVersion: k0smotron.io/v1beta1
   kind: Cluster
   metadata:
     name: k0smotron-test
   spec:
     replicas: 3
     service:
       type: LoadBalancer
     kineDataSourceSecretName: database-credentials
   EOF
   

   !!! note

   The secret must be in the same namespace as the cluster and the key
   must be `K0SMOTRON_KINE_DATASOURCE_URL`.