Requirements and Tips for Configuring Replication

This page provides information about working with read replicas. For information about how to configure a read replica, see Creating Read Replicas.

Read replicas are Cloud SQL instances that replicate from a Cloud SQL master instance.

Availability

  • Read replicas do not provide high availability; for that, you must configure your master instance for high availability.
  • Read replicas are not highly available. If they are located in a zone that experiences a general outage, they go offline.
  • Read replicas do not support the maintenance window setting; they can experience a disruptive upgrade at any time.
  • If the master instance fails over, read replicas do not change zones. Until the master fails back to its original zone, read replicas are in a different zone than the master instance.

Operations

  • You can create multiple read replicas for a single master instance. Cloud SQL does not provide load balancing between replicas.
  • The settings of the master instance are propagated to the replica, including the password for the postgres user and changes to the user table.
  • Read replicas can have more CPUs and memory than the master instance, but they cannot have less.
  • Read replicas must be in the same region as the master instance.
  • You cannot make changes to the user table on the replica. All user changes must be done on the master instance.
  • You cannot configure backups on the replica.
  • You cannot restore the master of a replica while the replica exists. Before restoring an instance from a backup, you must promote or delete all of its replicas.
  • Before you can delete a master instance, you must promote all of its read replicas to stand-alone instances or delete the read replicas.
  • You cannot create a replica of a replica.

Billing

  • A read replica is charged at the same rate as a standard Cloud SQL instance. There is no charge for the data replication.

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