# Using a read replica to reduce downtime when upgrading an RDS for MariaDB database
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In most cases, a blue/green deployment is the best option to reduce downtime when upgrading a MariaDB DB instance. For more information, see [Using Amazon RDS Blue/Green Deployments for database updates](blue-green-deployments.md). 

If you can't use a blue/green deployment and your MariaDB DB instance is currently in use with a production application, you can use the following procedure to upgrade the database version for your DB instance. This procedure can reduce the amount of downtime for your application. 

By using a read replica, you can perform most of the maintenance steps ahead of time and minimize the necessary changes during the actual outage. With this technique, you can test and prepare the new DB instance without making any changes to your existing DB instance.

The following procedure shows an example of upgrading from MariaDB version 10.5 to MariaDB version 10.6. You can use the same general steps for upgrades to other major versions. 

**To upgrade a MariaDB database while a DB instance is in use**

1. Sign in to the AWS Management Console and open the Amazon RDS console at [https://console.aws.amazon.com/rds/](https://console.aws.amazon.com/rds/).

1. Create a read replica of your MariaDB 10.5 DB instance. This process creates an upgradable copy of your database. Other read replicas of the DB instance might also exist.

   1. In the console, choose **Databases**, and then choose the DB instance that you want to upgrade.

   1. For **Actions**, choose **Create read replica**.

   1. Provide a value for **DB instance identifier** for your read replica and ensure that the **DB instance class** and other settings match your MariaDB 10.5 DB instance.

   1. Choose **Create read replica**.

1. (Optional) When the read replica has been created and **Status** shows **Available**, convert the read replica into a Multi-AZ deployment and enable backups.

   By default, a read replica is created as a Single-AZ deployment with backups disabled. Because the read replica ultimately becomes the production DB instance, it is a best practice to configure a Multi-AZ deployment and enable backups now.

   1. In the console, choose **Databases**, and then choose the read replica that you just created.

   1. Choose **Modify**.

   1. For **Multi-AZ deployment**, choose **Create a standby instance**.

   1. For **Backup Retention Period**, choose a positive nonzero value, such as 3 days, and then choose **Continue**.

   1. For **Scheduling of modifications**, choose **Apply immediately**.

   1. Choose **Modify DB instance**.

1. When the read replica **Status** shows **Available**, upgrade the read replica to MariaDB 10.6.

   1. In the console, choose **Databases**, and then choose the read replica that you just created.

   1. Choose **Modify**.

   1. For **DB engine version**, choose the MariaDB 10.6 version to upgrade to, and then choose **Continue**.

   1. For **Scheduling of modifications**, choose **Apply immediately**.

   1. Choose **Modify DB instance** to start the upgrade. 

1. When the upgrade is complete and **Status** shows **Available**, verify that the upgraded read replica is up-to-date with the source MariaDB 10.5 DB instance. To verify, connect to the read replica and run the `SHOW REPLICA STATUS` command. If the `Seconds_Behind_Master` field is `0`, then replication is up-to-date.
**Note**  
Previous versions of MariaDB used `SHOW SLAVE STATUS` instead of `SHOW REPLICA STATUS`. If you are using a MariaDB version before 10.6, then use `SHOW SLAVE STATUS`. 

1. (Optional) Create a read replica of your read replica.

   If you want the DB instance to have a read replica after it is promoted to a standalone DB instance, you can create the read replica now.

   1. In the console, choose **Databases**, and then choose the read replica that you just upgraded.

   1. For **Actions**, choose **Create read replica**.

   1. Provide a value for **DB instance identifier** for your read replica and ensure that the **DB instance class** and other settings match your MariaDB 10.5 DB instance.

   1. Choose **Create read replica**.

1. (Optional) Configure a custom DB parameter group for the read replica.

   If you want the DB instance to use a custom parameter group after it is promoted to a standalone DB instance, you can create the DB parameter group now and associate it with the read replica.

   1. Create a custom DB parameter group for MariaDB 10.6. For instructions, see [Creating a DB parameter group in Amazon RDS](USER_WorkingWithParamGroups.Creating.md).

   1. Modify the parameters that you want to change in the DB parameter group you just created. For instructions, see [Modifying parameters in a DB parameter group in Amazon RDS](USER_WorkingWithParamGroups.Modifying.md).

   1. In the console, choose **Databases**, and then choose the read replica.

   1. Choose **Modify**.

   1. For **DB parameter group**, choose the MariaDB 10.6 DB parameter group you just created, and then choose **Continue**.

   1. For **Scheduling of modifications**, choose **Apply immediately**.

   1. Choose **Modify DB instance** to start the upgrade. 

1. Make your MariaDB 10.6 read replica a standalone DB instance. 
**Important**  
When you promote your MariaDB 10.6 read replica to a standalone DB instance, it is no longer a replica of your MariaDB 10.5 DB instance. We recommend that you promote your MariaDB 10.6 read replica during a maintenance window when your source MariaDB 10.5 DB instance is in read-only mode and all write operations are suspended. When the promotion is completed, you can direct your write operations to the upgraded MariaDB 10.6 DB instance to ensure that no write operations are lost.  
In addition, we recommend that, before promoting your MariaDB 10.6 read replica, you perform all necessary data definition language (DDL) operations on your MariaDB 10.6 read replica. An example is creating indexes. This approach avoids negative effects on the performance of the MariaDB 10.6 read replica after it has been promoted. To promote a read replica, use the following procedure.

   1. In the console, choose **Databases**, and then choose the read replica that you just upgraded.

   1. For **Actions**, choose **Promote**.

   1. Choose **Yes** to enable automated backups for the read replica instance. For more information, see [Introduction to backups](USER_WorkingWithAutomatedBackups.md).

   1. Choose **Continue**.

   1. Choose **Promote Read Replica**.

1. You now have an upgraded version of your MariaDB database. At this point, you can direct your applications to the new MariaDB 10.6 DB instance.