AWS Transform MGN (formerly Application Migration Service)

AWS Transform MGN automates the rehosting of physical, virtual and other-cloud servers onto Amazon EC2. It replicates each source server continuously at block level, converts the disks for launch on AWS, and allows a test instance to be booted from the replica before a cutover is committed. The service was called AWS Application Migration Service (MGN) until AWS folded it into the AWS Transform family; the mgn API namespace, console URL and agent are unchanged.

It is the successor to two earlier tools. AWS Server Migration Service (SMS) was retired — its documentation has been withdrawn and its product page now serves AWS Transform MGN — and CloudEndure Migration was absorbed into it.

What it does

• Rehost, not replatform. The server arrives on EC2 as it was, with the same operating system, packages and configuration. Modernisation happens afterwards.
• Broad source support. Physical servers, VMware and Hyper-V virtual machines, and instances in other clouds, running Windows Server or a range of Linux distributions.
• Continuous replication. An agent on the source server ships block-level changes into a staging area in the target AWS account, so the replica stays current while the cutover is planned.
• Test before cutover. Test instances launch from the replicated volumes for validation, and only then does the cutover run. The cutover window is bounded by boot time rather than by copy time.
• Waves. Servers group into applications and applications into waves, so launch, cutover and archival can be driven in bulk across a large estate.

Recovery objectives

Because replication is continuous and cutover is a boot, the recovery point objective is measured in sub-seconds of data and the recovery time objective in minutes — the time the operating system takes to start. Those are properties of the replication design, not a service-level guarantee; validate them against the actual servers during the test launch.

What it costs

Replication of a given source server is free for the first 2,160 hours — 90 days of continuous use — after which that server is charged per hour for as long as it keeps replicating. The service fee is not the whole bill: throughout replication, testing and cutover, normal EC2 and EBS charges apply to the staging, test and target instances and their volumes. Budget a large wave on the infrastructure, not on the service being “free”.

Where it fits

MGN is the tool behind the rehost strategy in the seven Rs. For databases, AWS DMS usually beats rehosting the database server. For file and object data, DataSync moves the bulk without moving the server at all.