# Using a read replica to reduce downtime when upgrading an RDS for MySQL database
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In most cases, a blue/green deployment is the best option to reduce downtime when upgrading a MySQL 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 MySQL 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 MySQL version 5.7 to MySQL version 8.0. You can use the same general steps for upgrades to other major versions. You can use the same general steps for upgrades to other major versions.

**Note**  
When you are upgrading from MySQL version 5.7 to MySQL version 8.0, or from MySQL version 8.0 to MySQL version 8.4, complete the prechecks before performing the upgrade. For more information, see [Prechecks for upgrades from MySQL 5.7 to 8.0](USER_UpgradeDBInstance.MySQL.Major.md#USER_UpgradeDBInstance.MySQL.57to80Prechecks) and [Prechecks for upgrades from MySQL 8.0 to 8.4](USER_UpgradeDBInstance.MySQL.Major.md#USER_UpgradeDBInstance.MySQL.80to84Prechecks).

**To upgrade a MySQL 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 MySQL 5.7 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 MySQL 5.7 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 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.

   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 MySQL 8.0:

   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 MySQL 8.0 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 MySQL 5.7 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 MySQL used `SHOW SLAVE STATUS` instead of `SHOW REPLICA STATUS`. If you are using a MySQL version before 8.0.23, 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 MySQL 5.7 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 MySQL 8.0. 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 MySQL 8.0 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 MySQL 8.0 read replica a standalone DB instance. 
**Important**  
When you promote your MySQL 8.0 read replica to a standalone DB instance, it is no longer a replica of your MySQL 5.7 DB instance. We recommend that you promote your MySQL 8.0 read replica during a maintenance window when your source MySQL 5.7 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 MySQL 8.0 DB instance to ensure that no write operations are lost.  
In addition, we recommend that, before promoting your MySQL 8.0 read replica, you perform all necessary data definition language (DDL) operations on your MySQL 8.0 read replica. An example is creating indexes. This approach avoids negative effects on the performance of the MySQL 8.0 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 MySQL database. At this point, you can direct your applications to the new MySQL 8.0 DB instance.