# Use MySQL Read Replicas

MySQL read replicas provide improved performance by distributing read queries, thus reducing the load on the primary database. 
They also enhance high availability, scalability, and disaster recovery. 
Additionally, replicas can be placed in different geographical zones to further improve availability and reduce latency.

### Creating a Read Replica

To create a read replica for an existing MYSQL database in another zone, you can use the following command:

```bash
exo api --zone at-vie-1 create-dbaas-service-mysql rocket <<EOF
{
  "name": "rocket",
  "plan": "startup-8",
  "integrations": [{"type": "read_replica", "source-service": "launch-site"}]
}
EOF
```

This will create an instance called **rocket** in Zone AT-VIE-1 for an existing database called **launch-site**.

> [!NOTE]
> Do not forget to configure the IP Filter to access the new database.


### Verifying the Replica

`SHOW SLAVE STATUS` is the command in MySQL that provides information about the replication status of a replica (slave) server. 
It includes details about the slave I/O and SQL threads, the replication position, and any errors.

Run the following SQL query on the replica server:
```bash
SHOW SLAVE STATUS\G
```

This command outputs detailed information such as `Slave_IO_State`, `Master_Host`, `Master_User`, `Master_Log_File`, and `Seconds_Behind_Master`.


### Promoting the Replica to Master

Step 1: Get details of the replica service to find the **integration ID**

```bash
exo api get-dbaas-service-mysql -z at-vie-1 rocket
```

Step 2: Check Integration Status

```bash
exo api get-dbaas-integration <integration_id>
```

Step 3: Promote Replica to a master Database (Remove Replication)
```bash
exo api delete-dbaas-integration <integration_id>
```

> [!NOTE]
> Customers can create a read replica on a startup plan, regardless of the main cluster's plan. The read replica node is 
> vertically scalable. It can be horizontally scaled by promoting it to the primary, becoming a standalone service detached 
> from the main cluster.