# Adding Aurora Replicas to a DB cluster
An Aurora DB cluster with replication has one primary DB instance and up to 15 Aurora Replicas. The primary DB instance supports read and write operations, and performs all data modifications to the cluster volume. Aurora Replicas connect to the same storage volume as the primary DB instance, but support read operations only. You use Aurora Replicas to offload read workloads from the primary DB instance. For more information, see [Aurora Replicas](Aurora.Replication.md#Aurora.Replication.Replicas).
Amazon Aurora Replicas have the following limitations:
+ However, you can add reader instances to Aurora serverless DB clusters. For more information, see [Adding an Aurora serverless reader](aurora-serverless-v2-administration.md#aurora-serverless-v2-adding-reader).
We recommend that you distribute the primary instance and Aurora Replicas of your Aurora DB cluster over multiple Availability Zones to improve the availability of your DB cluster. For more information, see [Region availability](Concepts.RegionsAndAvailabilityZones.md#Aurora.Overview.Availability).
To remove an Aurora Replica from an Aurora DB cluster, delete the Aurora Replica by following the instructions in [Deleting a DB instance from an Aurora DB cluster](USER_DeleteCluster.md#USER_DeleteInstance).
**Note**
Amazon Aurora also supports replication with an external database, such as an RDS DB instance. The RDS DB instance must be in the same Amazon Region as Amazon Aurora. For more information, see [Replication with Amazon Aurora](Aurora.Replication.md).
You can add Aurora Replicas to a DB cluster using the Amazon Web Services Management Console, the Amazon CLI, or the RDS API.
## Console
**To add an Aurora replica to a DB cluster**
1. Sign in to the Amazon Web Services Management Console and open the Amazon RDS console at [https://console.amazonaws.cn/rds/](https://console.amazonaws.cn/rds/).
1. In the navigation pane, choose **Databases**, and then select the DB cluster where you want to add the new DB instance.
1. Make sure that both the cluster and the primary instance are in the **Available** state. If the DB cluster or the primary instance are in a transitional state such as **Creating**, you can't add a replica.
If the cluster doesn't have a primary instance, create one using the [create-db-instance](https://docs.amazonaws.cn/cli/latest/reference/rds/create-db-instance.html) Amazon CLI command. This situation can arise if you used the CLI to restore a DB cluster snapshot and then view the cluster in the Amazon Web Services Management Console.
1. For **Actions**, choose **Add reader**.
The **Add reader** page appears.
1. On the **Add reader** page, specify options for your Aurora Replica. The following table shows settings for an Aurora Replica.
[See the AWS documentation website for more details](http://docs.amazonaws.cn/en_us/AmazonRDS/latest/AuroraUserGuide/aurora-replicas-adding.html)
1. Choose **Add reader** to create the Aurora Replica.
## Amazon CLI
To create an Aurora Replica in your DB cluster, run the [create-db-instance](https://docs.amazonaws.cn/cli/latest/reference/rds/create-db-instance.html) Amazon CLI command. Include the name of the DB cluster as the `--db-cluster-identifier` option. You can optionally specify an Availability Zone for the Aurora Replica using the `--availability-zone` parameter, as shown in the following examples.
For example, the following command creates a new MySQL 5.7–compatible Aurora Replica named `sample-instance-us-west-2a`.
For Linux, macOS, or Unix:
```
aws rds create-db-instance --db-instance-identifier sample-instance-us-west-2a \
--db-cluster-identifier sample-cluster --engine aurora-mysql --db-instance-class db.r5.large \
--availability-zone us-west-2a
```
For Windows:
```
aws rds create-db-instance --db-instance-identifier sample-instance-us-west-2a ^
--db-cluster-identifier sample-cluster --engine aurora-mysql --db-instance-class db.r5.large ^
--availability-zone us-west-2a
```
The following command creates a new MySQL 5.7–compatible Aurora Replica named `sample-instance-us-west-2a`.
For Linux, macOS, or Unix:
```
aws rds create-db-instance --db-instance-identifier sample-instance-us-west-2a \
--db-cluster-identifier sample-cluster --engine aurora-mysql --db-instance-class db.r5.large \
--availability-zone us-west-2a
```
For Windows:
```
aws rds create-db-instance --db-instance-identifier sample-instance-us-west-2a ^
--db-cluster-identifier sample-cluster --engine aurora --db-instance-class db.r5.large ^
--availability-zone us-west-2a
```
The following command creates a new PostgreSQL-compatible Aurora Replica named `sample-instance-us-west-2a`.
For Linux, macOS, or Unix:
```
aws rds create-db-instance --db-instance-identifier sample-instance-us-west-2a \
--db-cluster-identifier sample-cluster --engine aurora-postgresql --db-instance-class db.r5.large \
--availability-zone us-west-2a
```
For Windows:
```
aws rds create-db-instance --db-instance-identifier sample-instance-us-west-2a ^
--db-cluster-identifier sample-cluster --engine aurora-postgresql --db-instance-class db.r5.large ^
--availability-zone us-west-2a
```
## RDS API
To create an Aurora Replica in your DB cluster, call the [CreateDBInstance](https://docs.amazonaws.cn/AmazonRDS/latest/APIReference/API_CreateDBInstance.html) operation. Include the name of the DB cluster as the `DBClusterIdentifier` parameter. You can optionally specify an Availability Zone for the Aurora Replica using the `AvailabilityZone` parameter.
For information about Auto Scaling Amazon Aurora with Aurora replicas, see the following sections.
**Topics**
+ [Amazon Aurora Auto Scaling with Aurora Replicas](Aurora.Integrating.AutoScaling.md)
+ [Adding an auto scaling policy to an Amazon Aurora DB cluster](Aurora.Integrating.AutoScaling.Add.md)
+ [Editing an auto scaling policy for an Amazon Aurora DB cluster](Aurora.Integrating.AutoScaling.Edit.md)
+ [Deleting an auto scaling policy from your Amazon Aurora DB cluster](Aurora.Integrating.AutoScaling.Delete.md)