Mattermost has two configuration settings for database connection strings. It has a string setting for the master/writer DB endpoint "SqlSettings.DataSource" and it has an array setting for read replica DB endpoint "SqlSettings.DataSourceReplicas".
Right now when the cloud provisioner creates a ClusterInstallation k8s manifest and applies it, it does not specify the read replica endpoint in "SqlSettings.DataSourceReplicas" so the installations are only using the master/writer DB endpoint for everything.
We need to update the provisioner to set "SqlSettings.DataSourceReplicas" to an array of 1 with that 1 item containing the read replica DB connection string.
Do this for the "aws-multitenant-rds-postgres" installation database type. We can create further tickets to update the other database types as needed.
No testing required.