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 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
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 db1
juju switch lisbon
juju deploy postgresql db2
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.
For example:
juju add-unit db1 -n 2 -m rome
juju add-unit db2 -n 2 -m lisbon
Note: Scaling is possible before and after the asynchronous replication is established/created.