# Creating a read replica
<a name="USER_ReadRepl.Create"></a>

You can create a read replica from an existing DB instance using the AWS Management Console, AWS CLI, or RDS API. You create a read replica by specifying `SourceDBInstanceIdentifier`, which is the DB instance identifier of the source DB instance that you want to replicate from.

When you create a read replica, Amazon RDS takes a DB snapshot of your source DB instance and begins replication. The source DB instance experiences a very brief I/O suspension when the DB snapshot operation begins. The I/O suspension typically lasts about one second. You can avoid the I/O suspension if the source DB instance is a Multi-AZ deployment, because in that case the snapshot is taken from the secondary DB instance.

An active, long-running transaction can slow the process of creating the read replica. We recommend that you wait for long-running transactions to complete before creating a read replica. If you create multiple read replicas in parallel from the same source DB instance, Amazon RDS takes only one snapshot at the start of the first create action.

When creating a read replica, there are a few things to consider. First, you must enable automatic backups on the source DB instance by setting the backup retention period to a value other than 0. This requirement also applies to a read replica that is the source DB instance for another read replica. To enable automatic backups on an RDS for MySQL read replica, first create the read replica, then modify the read replica to enable automatic backups.

**Note**  
Within an AWS Region, we strongly recommend that you create all read replicas in the same virtual private cloud (VPC) based on Amazon VPC as the source DB instance. If you create a read replica in a different VPC from the source DB instance, classless inter-domain routing (CIDR) ranges can overlap between the replica and the RDS system. CIDR overlap makes the replica unstable, which can negatively impact applications connecting to it. If you receive an error when creating the read replica, choose a different destination DB subnet group. For more information, see [Working with a DB instance in a VPC](USER_VPC.WorkingWithRDSInstanceinaVPC.md).  
There is no direct way to create a read replica in another AWS account using the console or AWS CLI.

## Console
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**To create a read replica from a source DB instance**

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. In the navigation pane, choose **Databases**.

1. Choose the DB instance that you want to use as the source for a read replica.

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

1. For **DB instance identifier**, enter a name for the read replica.

1. Choose your instance configuration. We recommend that you use the same or larger DB instance class and storage type as the source DB instance for the read replica.

1. For **AWS Region**, specify the destination Region for the read replica.

1. For **Storage**, specify the allocated storage size and whether you want to use storage autoscaling.

   If your source DB instance isn't on the latest storage configuration, the **Upgrade storage file system configuration** option is available. You can enable this setting to upgrade the storage file system of the read replica to the preferred configuration. For more information, see [Upgrading the storage file system for a DB instance](USER_PIOPS.UpgradeFileSystem.md).

1. For **Availability**, choose whether to create a standby of your replica in another Availability Zone for failover support for the replica.
**Note**  
Creating your read replica as a Multi-AZ DB instance is independent of whether the source database is a Multi-AZ DB instance.

1. Specify other DB instance settings. For information about each available setting, see [Settings for DB instances](USER_CreateDBInstance.Settings.md).

1. To create an encrypted read replica, expand **Additional configuration** and specify the following settings:

   1. Choose **Enable encryption**.

   1. For **AWS KMS key**, choose the AWS KMS key identifier of the KMS key.
**Note**  
 The source DB instance must be encrypted. To learn more about encrypting the source DB instance, see [Encrypting Amazon RDS resources](Overview.Encryption.md).

1. Choose **Create read replica**.

After the read replica is created, you can see it on the **Databases** page in the RDS console. It shows **Replica** in the **Role** column.

## AWS CLI
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To create a read replica from a source DB instance, use the AWS CLI command [create-db-instance-read-replica](https://docs.aws.amazon.com/cli/latest/reference/rds/create-db-instance-read-replica.html). This example also sets the allocated storage size, enables storage autoscaling, and upgrades the file system to the preferred configuration.

You can specify other settings. For information about each setting, see [Settings for DB instances](USER_CreateDBInstance.Settings.md).

**Example**  
For Linux, macOS, or Unix:  

```
aws rds create-db-instance-read-replica \
    --db-instance-identifier myreadreplica \
    --source-db-instance-identifier mydbinstance \
    --allocated-storage 100 \
    --max-allocated-storage 1000 \
    --upgrade-storage-config
```
For Windows:  

```
aws rds create-db-instance-read-replica ^
    --db-instance-identifier myreadreplica ^
    --source-db-instance-identifier mydbinstance ^
    --allocated-storage 100 ^
    --max-allocated-storage 1000 ^
    --upgrade-storage-config
```

## RDS API
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To create a read replica from a source Db2, MySQL, MariaDB, Oracle, PostgreSQL, or SQL Server DB instance, call the Amazon RDS API [CreateDBInstanceReadReplica](https://docs.aws.amazon.com/AmazonRDS/latest/APIReference/API_CreateDBInstanceReadReplica.html) operation with the following required parameters:
+ `DBInstanceIdentifier`
+ `SourceDBInstanceIdentifier`

**Note**  
 To create an RDS for Db2 standby replica, set the optional `ReplicaMode` operation to `mounted`.