Planning and Executing Large-Scale Migrations with AWS MGN - Wave Design and Cutover Automation
Plan migrations of hundreds of servers using wave design, automate cutover with post-launch scripts, and optimize instances after migration.
Wave Design Principles
In large-scale migrations, you don't migrate all servers at once. Instead, you divide them into waves (migration batches) and execute them in stages. Wave design is based on application dependencies. Applications with tightly coupled web servers, application servers, and database servers should be placed in the same wave and cut over simultaneously. The first wave typically consists of low-risk applications (development environments, internal tools) to validate and refine the migration process. Subsequent waves handle production applications, and the final wave migrates the most critical systems. This phased approach is the standard practice.
Cutover Automation
MGN's post-launch actions automatically execute scripts on EC2 instances after cutover. Integrated with Systems Manager Run Command, they can automate DNS record updates, monitoring agent installation, application configuration changes, and health checks. Application templates standardize the EC2 configuration for target instances (instance type, subnet, security group, IAM role, tags), applying consistent settings to servers with the same role. Since the same template is used for both test launches and cutover, configuration drift between test and production environments is eliminated.
Post-Migration Optimization
Immediately after migration, run EC2 instances with the same specs as the on-premises servers and verify stability. After 2-4 weeks of operational data accumulates, right-size instance types based on AWS Compute Optimizer recommendations. Many on-premises servers were over-provisioned, and right-sizing can yield 30-50% cost savings. Consider migrating to Graviton (Arm-based) instances as well, which can deliver up to 40% cost reduction at equivalent performance. Post-migration optimization is not a one-time event. Establish a process to regularly review Compute Optimizer recommendations and continuously optimize costs. For a systematic approach to server migration from basics to advanced topics, books on Amazon offer comprehensive coverage.
MGN Pricing
MGN itself is free to use. Costs come from replication EC2 instances (lightweight t3.small instances created automatically), EBS volumes (for storing replication data), and EC2 charges for test and cutover instances. Since replication incurs ongoing costs, shortening the migration period is key to cost optimization. Terminate test instances promptly after validation, and stop replication for source servers after cutover.
Summary
The keys to successful large-scale migration are phased execution through wave design, cutover automation via post-launch actions, and post-migration optimization with Compute Optimizer. By combining MGN and Migration Hub, you can centrally manage migrations of hundreds of servers, minimizing risk while completing the migration efficiently.