AWS Database Migration Service
Step-by-Step Migration Guide (API Version 2016-01-01)

Step 5: Create an AWS DMS Replication Instance

After validating the schema structure between source and target databases, continue with the core part of this walkthrough, which is the data migration. The following illustration shows a high-level view of the migration process.

                     AWS DMS migration process diagram showing source and target databases and
                        the AWS DMS replication instance

An AWS DMS replication instance performs the actual data migration between source and target. The replication instance also caches the transaction logs during the migration. The amount of CPU and memory capacity a replication instance has influences the overall time that is required for the migration.

For information about best practices for using AWS DMS, see AWS Database Migration Service Best Practices.

To create an AWS DMS replication instance

  1. Sign in to the AWS Management Console, and open the AWS DMS console at

  2. In the console, choose Create migration. If you are signed in as an AWS Identity and Access Management (IAM) user, you must have the appropriate permissions to access AWS DMS. For more information about the permissions required, see IAM Permissions Needed to Use AWS DMS.

  3. On the Welcome page, choose Next to start a database migration.

  4. On the Create replication instance page, specify your replication instance information.

    Parameter Description


    Select a name for your replication instance. If you are using multiple replication servers or sharing an account, choose a name that helps you quickly differentiate between the different servers.


    Type a brief description.

    Instance class

    Select the type of replication server to create. Each size and type of instance class has increasing CPU, memory, and I/O capacity. Generally, t2 instances are for lower load tasks, and the c4 instances are for higher load and more tasks.


    Choose the virtual private cloud (VPC) in which your replication instance will launch. If possible, select the same VPC in which either your source or target database resides (or both).


    If you choose Yes, AWS DMS creates a second replication server in a different Availability Zone for failover if there is a problem with the primary replication server.

    Publicly accessible

    If either your source or target database resides outside of the VPC in which your replication server resides, you must make your replication server policy publicly accessible.

  5. For the Advanced section, specify the following information.

    Parameter Description

    Allocated storage (GB)

    Amount of storage on the replication server for the AWS DMS task logs, including historical tasks logs. AWS DMS also uses disk storage to cache certain data while it replicates it from the source database to the target. Additionally, more storage generally enables better IOPS on the server.

    Replication Subnet Group

    If you are running in a Multi-AZ configuration, you need at least two subnet groups.

    Availability zone

    Generally, performance is better if you locate your primary replication server in the same Availability Zone as your target database.

    VPC Security Group(s)

    Security groups enable you to control ingress and egress to your VPC. AWS DMS lets you associate one or more security groups with the VPC in which your replication server is launched.

    KMS master key

    With AWS DMS, all data is encrypted at rest using a KMS encryption key. By default, AWS DMS creates a new encryption key for your replication server. However, you might choose to use an existing key.

    For information about the KMS master key, see Setting an Encryption Key and Specifying KMS Permissions.

  6. Click Next.