Set up logical replication

This guide demonstrates how to configure logical replication on your CrateDB Cloud cluster. Logical replication is a mechanism by which data can be copied across multiple clusters. CrateDB uses a publish and subscribe model where subscribers pull data from the publications of the publisher they subscribed to.

This guide only provides an example of configuration in the context of Cloud clusters. For a full documentation and all use-cases of logical replication see the full documentation.

To get started, you will need to deploy some clusters first. Head over to Cloud Console to do that.

Table of contents

Configure logical replication

Logical replication uses publication-subscription system. A publication is created on a cluster from which the data should be copied, and a subscription is created on a cluster where the data should be copied to.

Create a publication on Cluster 1

Example publication:

CREATE PUBLICATION mypublication
FOR ALL TABLES

Create a subscription on Cluster 2

Example subscription:

CREATE SUBSCRIPTION mysubscription
CONNECTION 'crate://your-cluster-url.cratedb.net?mode=pg_tunnel&user=your_user&password=your_password'
PUBLICATION mypublication;

Note

By default, CrateDB uses the transport protocol (on port 4300) for logical replication. If the port is not available (such as with CrateDB Cloud), the mode=pg_tunnel can be used to tunnel over the Postgres protocol (port 5432).

That’s it in terms of configuration. Data from Cluster 1 will now be automatically replicated on Cluster 2. This feature can also be configured on multiple clusters, for example you could create another subscription on Cluster 3 to ensure high availability.

Disable logical replication

To disable the feature you need to remove the publication from the cluster that serves as the datasource, and remove the subscription from the cluster that serves as the target.

Remove a publication from Cluster 1

Example publication:

DROP PUBLICATION mypublication

Remove a subscription from Cluster 2

Example subscription:

DROP SUBSCRIPTION mysubscription

Conclusion

This is a configuration that works out-of-the-box on CrateDB Cloud Cluster. For all the configuration options see the full logical replication documentation.