Replication server configuration - AWS Elastic Disaster Recovery

Replication server configuration

Replication servers are lightweight Amazon EC2 instances that are used to replicate data between your source servers and AWS. Replication servers are automatically launched and terminated as needed. You can modify the behavior of the replication servers by modifying the settings for a single source server or multiple source servers. Alternatively, you can run Elastic Disaster Recovery with the default replication server settings.

You can configure a variety of replication server options, including:

  • The subnet within which the replication server will be launched

  • Replication server instance type

  • Whether a dedicated instance is used for the replication server


Replication servers are only supported on x86_64 CPU architecture instance types.

Staging area subnet

Choose the Staging area subnet that you want to allocate as the staging area subnet for all of your replication servers.

The best practice is to create a single dedicated, separate subnet for all of your recovery waves using your AWS Account. Learn more about creating subnets in this AWS VPC article.

The Staging Area Subnet is the subnet within which replication servers subnet in this AWS VPC article.

If a default subnet does not exist, select a specific subnet. The drop-down menu contains a list of all subnets that are available in the current AWS Region.


Changing the subnet does not significantly interfere with ongoing data replication, although there may be a minor delay of several minutes while the servers are moved from one subnet to another.

Using multiple subnets

The best practice is to use a single staging area subnet for all of your recovery waves within a single AWS Account. You may want to use multiple subnets in certain cases, such as the recovery of thousands of servers.


Using more than one staging area subnet might result in higher compute consumption as more replication servers will be needed.

Launching replication servers in Availability Zones

If you want your replication servers to be launched in a specific Availability Zone, then select or create a subnet in that specific Availability Zone. Learn more about using Availability Zones in this Amazon EC2 article.

Replication server instance type

Choose the Replication server instance type. This will determine the instance type and size that will be used for the launch of each replication server.

The best practice is to not change the default replication server instance type unless there is a business need for doing so.

By default, Elastic Disaster Recovery utilizes the t3.small instance type. This is the most cost effective instance type and should work well for most common workloads. You can change the replication server instance type to speed up the initial sync of data from your source servers to AWS. Changing the instance type will likely lead to increased compute costs.

You can change the Replication server instance type to any type you wish. The dropdown menu contains all available instance types. Recommended and commonly used instance types are displayed first.

You can search for a specific instance type within the search box.

The replication server instance type can be changed for servers that are replicating too slowly or servers that are constantly busy or experience frequent spikes. These are the most common instance type changes that are made:

  • Servers with less than 26 disks – Change the instance type to m5.large. Increase the instance type to m5.xl or higher as needed.

  • Servers with more than 26 disks (or servers in AWS Regions that do not support m5 instance types) – Change the instance type to m4.large. Increase to m4.xlarge or higher, as needed.

  • Changing the replication server instance type will not affect data replication. Data replication will automatically continue from where it left off, using the new instance type you selected.

  • By default, replication servers are automatically assigned a public IP address from Amazon's public IP space.

Dedicated instance for replication server

Choose whether you would like to use a Dedicated instance for replication server.

When an external server is very write-intensive, the replication of data from its disks to a shared replication server can interfere with the data replication of other servers. In these cases you should choose the Use dedicated replication server option (and also consider changing Replication server instance type).

Otherwise, choose the Do not use dedicated replication server option.


Using a dedicated replication server may increase the EC2 cost you incur during replication.