Set up clusters for cross-regional async replication

Cross-regional (or multi-server) asynchronous replication focuses on disaster recovery by distributing data across different servers.

This guide will show you the basics of initiating a cross-regional async setup using an example PostgreSQL K8s deployment with two servers: one in Rome and one in Lisbon.

Prerequisites

• Juju v.3.4.2+
• Make sure your machine(s) fulfill the system requirements
• See supported target/source model relationships.

Summary

• Deploy
• Offer
• Consume
• Promote or switchover a cluster
• Scale a cluster

Deploy

To deploy two clusters in different servers, create two juju models - one for the rome cluster, one for the lisbon cluster. In the example below, we use the config flag profile=testing to limit memory usage.

juju add-model rome 
juju add-model lisbon

juju switch rome # active model must correspond to cluster
juju deploy postgresql-k8s db1 --trust --channel=14/edge --config profile=testing --base ubuntu@22.04

juju switch lisbon
juju deploy postgresql-k8s db2 --trust --channel=14/edge --config profile=testing --base ubuntu@22.04

Offer

Offer asynchronous replication in one of the clusters.

juju switch rome
juju offer db1:replication-offer replication-offer

Consume

Consume asynchronous replication on planned Standby cluster (Lisbon):

juju switch lisbon
juju consume rome.replication-offer
juju integrate replication-offer db2:replication

Promote or switchover a cluster

To define the primary cluster, use the create-replication action.

juju run -m rome db1/leader create-replication

To switchover and use lisbon as the primary instead, run

juju run -m lisbon db2/leader promote-to-primary

Scale a cluster

The two clusters work independently, which means that it’s possible to scale each cluster separately. The -m flag defines the target of this action, so it can be performed within any active model.

juju scale-application db1 3 -m rome

juju scale-application db2 3 -m lisbon