# Adding a DB instance to an active-active cluster
<a name="mysql-active-active-clusters-adding"></a>

You can add a DB instance to an Amazon RDS for MySQL active-active cluster by restoring a DB snapshot or by restoring a DB instance to a point in time. An active-active cluster can include up to nine DB instances.

When you recover a DB instance to a point in time, it usually includes more recent transactions than a DB instance that was restored from a DB snapshot. When the DB instance has more recent transactions, fewer transactions need to be applied when you start replication. So, using point-in-time recovery to add a DB instance to a cluster is usually faster than restoring from a DB snapshot.

**Topics**
+ [Adding a DB instance to an active-active cluster using point-in-time recovery](#mysql-active-active-clusters-adding-pitr)
+ [Adding a DB instance to an active-active cluster using a DB snapshot](#mysql-active-active-clusters-adding-snapshot)

## Adding a DB instance to an active-active cluster using point-in-time recovery
<a name="mysql-active-active-clusters-adding-pitr"></a>

You can add a DB instance to an active-active cluster by performing point-in-time recovery on a DB instance in the cluster.

For information about recovering a DB instance to a point in time in a different AWS Region, see [Replicating automated backups to another AWS Region](USER_ReplicateBackups.md).

**To add a DB instance to an active-active cluster using point-in-time recovery**

1. Create a new DB instance by performing point-in-time recovery on a DB instance in the active-active cluster.

   You can perform point-in-time recovery on any DB instance in the cluster to create the new DB instance. For instructions, see [Restoring a DB instance to a specified time for Amazon RDS](USER_PIT.md).
**Important**  
During point-in-time-recovery, associate the new DB instance with a DB parameter group that has the active-active cluster parameters set. Otherwise, Group Replication won't start on the new DB instance. For information about the parameters and the required setting for each one, see [Required parameter settings for active-active clusters](mysql-active-active-clusters-parameters.md).
**Tip**  
If you take a snapshot of the DB instance before you start point-in-time recovery, you might be able to reduce the amount of time required to apply transactions on the new DB instance.

1. Add the DB instance to the `group_replication_group_seeds` parameter in each DB parameter group associated with a DB instance in the active-active cluster, including the DB parameter group that you associated with the new DB instance.

   For more information about setting parameters, see [Modifying parameters in a DB parameter group in Amazon RDS](USER_WorkingWithParamGroups.Modifying.md).

1. In a SQL client, connect to the new DB instance, and call the [mysql.rds\$1group\$1replication\$1set\$1recovery\$1channel](mysql-stored-proc-active-active-clusters.md#mysql_rds_group_replication_set_recovery_channel) stored procedure. Replace *group\$1replication\$1user\$1password* with the password for the `rdsgrprepladmin` user.

   ```
   call mysql.rds_group_replication_set_recovery_channel('group_replication_user_password');
   ```

1. Using the SQL client, call the [mysql.rds\$1group\$1replication\$1start](mysql-stored-proc-active-active-clusters.md#mysql_rds_group_replication_start) stored procedure to start replication:

   ```
   call mysql.rds_group_replication_start(0);
   ```

## Adding a DB instance to an active-active cluster using a DB snapshot
<a name="mysql-active-active-clusters-adding-snapshot"></a>

You can add a DB instance to an active-active cluster by creating a DB snapshot of a DB instance in the cluster and then restoring the DB snapshot.

For information about copying a snapshot to a different AWS Region, see [Considerations for cross-Region snapshot copying](USER_CopySnapshot.md#USER_CopySnapshot.AcrossRegions).

**To add a DB instance to an active-active cluster using a DB snapshot**

1. Create a DB snapshot of a DB instance in the active-active cluster.

   You can create a DB snapshot of any DB instance in the cluster. For instructions, see [Creating a DB snapshot for a Single-AZ DB instance for Amazon RDS](USER_CreateSnapshot.md).

1. Restore a DB instance from the DB snapshot.

   During the snapshot restore operation, associate the new DB instance with a DB parameter group that has the active-active cluster parameters set. For information about the parameters and the required setting for each one, see [Required parameter settings for active-active clusters](mysql-active-active-clusters-parameters.md).

   For information about restoring a DB instance from a DB snapshot, see [Restoring to a DB instance](USER_RestoreFromSnapshot.md).

1. Add the DB instance to the `group_replication_group_seeds` parameter in each DB parameter group associated with a DB instance in the active-active cluster, including the DB parameter group that you associated with the new DB instance.

   For more information about setting parameters, see [Modifying parameters in a DB parameter group in Amazon RDS](USER_WorkingWithParamGroups.Modifying.md).

1. In a SQL client, connect to the new DB instance, and call the [mysql.rds\$1group\$1replication\$1set\$1recovery\$1channel](mysql-stored-proc-active-active-clusters.md#mysql_rds_group_replication_set_recovery_channel) stored procedure. Replace *group\$1replication\$1user\$1password* with the password for the `rdsgrprepladmin` user.

   ```
   call mysql.rds_group_replication_set_recovery_channel('group_replication_user_password');
   ```

1. Using the SQL client, call the [mysql.rds\$1group\$1replication\$1start](mysql-stored-proc-active-active-clusters.md#mysql_rds_group_replication_start) stored procedure to start replication:

   ```
   call mysql.rds_group_replication_start(0);
   ```