Enabling local write forwarding - Amazon Aurora
Enabling write forwarding for database sessions

Enabling local write forwarding

By default, local write forwarding isn't enabled for Aurora MySQL DB clusters. You enable local write forwarding at the cluster level, not at the instance level.

Important

You can also enable local write forwarding for cross-Region read replicas that use binary logging, but write operations aren't forwarded to the source AWS Region. They're forwarded to the writer DB instance of the binlog read replica cluster.

Use this method only if you have a use case for writing to the binlog read replica in the secondary AWS Region. Otherwise, you might end up with a "split-brain" scenario where replicated datasets are inconsistent with each other.

We recommend that you use global write forwarding with global databases, rather than local write forwarding on cross-Region read replicas, unless absolutely necessary. For more information, see Using write forwarding in an Amazon Aurora global database.

Using the AWS Management Console, select the Turn on local write forwarding check box under Read replica write forwarding when you create or modify a DB cluster.

To enable write forwarding with the AWS CLI, use the --enable-local-write-forwarding option. This option works when you create a new DB cluster using the create-db-cluster command. It also works when you modify an existing DB cluster using the modify-db-cluster command. You can disable write forwarding by using the --no-enable-local-write-forwarding option with these same CLI commands.

The following example creates an Aurora MySQL DB cluster with write forwarding enabled.

aws rds create-db-cluster \
  --db-cluster-identifier write-forwarding-test-cluster \
  --enable-local-write-forwarding \
  --engine aurora-mysql \
  --engine-version 8.0.mysql_aurora.3.04.0 \
  --master-username myuser \
  --master-user-password mypassword \
  --backup-retention 1

You then create writer and reader DB instances so that you can use write forwarding. For more information, see Creating an Amazon Aurora DB cluster.

To enable write forwarding using the Amazon RDS API, set the EnableLocalWriteForwarding parameter to true. This parameter works when you create a new DB cluster using the CreateDBCluster operation. It also works when you modify an existing DB cluster using the ModifyDBCluster operation. You can disable write forwarding by setting the EnableLocalWriteForwarding parameter to false.

Enabling write forwarding for database sessions

The aurora_replica_read_consistency parameter is a DB parameter and DB cluster parameter that enables write forwarding. You can specify EVENTUAL, SESSION, or GLOBAL for the read consistency level. To learn more about consistency levels, see Read consistency for write forwarding.

The following rules apply to this parameter:

  • The default value is '' (null).

  • Write forwarding is available only if you set aurora_replica_read_consistency to EVENTUAL, SESSION, or GLOBAL. This parameter is relevant only in reader instances of DB clusters that have write forwarding enabled.

  • You can't set this parameter (when empty) or unset it (when already set) inside a multistatement transaction. You can change it from one valid value to another valid value during such a transaction, but we don't recommend this action.