Configuring database replication


Database replication involves configuring a master and slave database architecture, whereby the slave is an exact replica of the master at all times. This feature is supported for MySQL, PostgreSQL, Redis and MongoDB.

Database replication can be set up for a single application, between applications, or between database groups with various benefits:

For a single application with one DB group

For multiple database groups

For multiple applications


Replication between different applications is not supported for MongoDB.

How it works

When you start replicating your database, the Cloud 66 will do the following:

  1. Take a full backup of the master database server in your source application.
  2. Configure a secondary database to be a slave of the source database
  3. Configure the source database to act as the replication master of the secondary database
  4. The relevant environment variables are updated for use in your code and scripts

In the case of a single application, we create a secondary database server in your cloud and restore your backup to it. For databases that span applications, we restore your backup on the database server of the second application. For database groups you need to set up the new group first, and then set up replication once it is in place.

Similarly, when you disable replication, we do the following:

  1. We disable replication on your master database, and configure it to be a standalone database server
  2. The secondary database server is removed as a slave from the master database server on the source
  3. The source database server is configured as a standalone database server
  4. The relevant environment variables are updated for use in your code and scripts

Environment Variables

Cloud 66 generates and maintains a number of environment variables automatically on your servers, including those that hold the address for your database server.

When you enable database replication, we will generate additional environment variables for your slave server(s). The value of these variables will change when you enable or disable replication.

In the case that an environment variable contains multiple values, such as IP addresses, these are separated by comma.

Enable database replication

The process of enabling database replication varies slightly for a single application compared to replication between applications.


Database replication will disrupt the database serving your application during the replication configuration process. The disruption time depends entirely on your database type and size, and different databases may require a restart and/or a complete backup in order to warm-up the new server. This disruption will occur every time you scale your server.

Single application

To enable replication for a single application, you need to scale up to create a slave:

  1. Open the Application Overview from your Dashboard
  2. Click on the Servers tab
  3. Click the green + next to the database you want to replicate. This will allow you to choose your new server size. Your new server should be comparable to your master server.


You will not be able to scale your database up unless you have managed backups enabled.

Between database groups

Please see our full guide on database groups for details on how this works.

Between applications

To enable replication between applications, ensure that you have a secondary application deployed, and that its database server contains at least twice as much disk space as the size of your database backup. Then:

  1. Open the Application Overview for the secondary application from your Dashboard
  2. Click on the Servers tab
  3. Click on the name of the database server (this will become a slave of the source/master database)
  4. Click Configure data replication in the right sidebar, and select a source application (i.e the source/master database).
  5. Confirm to commence the replication process.

Disable database replication

To disable replication between applications:

Re-synchronizing slave with master

From time-to-time your slave database may go out of sync with its master. You can re-synchronize a slave in two ways: