Set up clusters for cross-regional async replication
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Contact the Canonical Data Platform team if you are interested in this topic.
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.
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-k8s db1 --trust --channel=14/candidate --config profile=testing --base ubuntu@22.04
juju switch lisbon
juju deploy postgresql-k8s db2 --trust --channel=14/candidate --config profile=testing --base ubuntu@22.04
Offer
Offer asynchronous replication in one of the clusters.
juju switch rome
juju offer db1:async-primary async-primary
Consume
Consume asynchronous replication on planned Standby cluster (Lisbon):
juju switch lisbon
juju consume rome.async-primary
juju integrate async-primary db2:async-replica
Promote or switchover a cluster
To define the primary cluster, use the promote-cluster action.
juju run -m rome db1/leader promote-cluster
To switchover and use lisbon as the primary instead, run
juju run -m lisbon db2/leader promote-cluster force-promotion=true
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
Note: Scaling is possible before and after the asynchronous replication is established/created.