AWS Migration Cutover Options

1. Traditional Network Cutover (DNS / IP / Routing Shift)

This is the standard approach when migrating workloads using replication tools like AWS Application Migration Service (MGN) or database migration tools.

How it Works

• Keep on-prem server running until the final synchronization.
• At cutover time, shift traffic by:
  • Updating DNS records
  • Changing routing / firewall rules
  • Moving virtual IPs in advanced setups

Pros

• Minimal downtime (often just minutes for DNS / TCP drain)
• Predictable transition if planned carefully
• Users often don’t notice

Cons

• Requires clean network alignment (firewalls, VPN/VPC connectivity, DNS changes)
• Higher operational complexity
• Harder in environments with legacy networks

2. Application Shutdown Option (Instead of Network Cutover)

A simpler and more controlled approach is to intentionally shut down the on-prem application during cutover, then bring it up only in AWS.

How it Works

1. Announce a maintenance window.
2. Shut down the application on-prem.
3. Finalize replication (last sync is clean, no data churn).
4. Start the migrated instance in AWS.
5. Run validation and open traffic to AWS version only.

Pros

• Radically simpler cutover (no real-time switch, no race conditions)
• Guarantees data consistency (no writes occurring during final sync)
• Eliminates risk of split-brain between on-prem and AWS
• Great for:
  • Stateful apps
  • Legacy apps
  • Systems with fragile network dependencies
  • Low-tolerance for replication errors

Cons

• Requires a downtime window
• Users may have to plan for brief outage
• Not suitable for real-time, 24×7 systems without maintenance windows

When Shutting Down Makes More Sense

Use this method when:

• The application cannot tolerate write divergence
• Networking between on-prem and AWS is unstable or complex
• DNS propagation impact is unpredictable
• Migrating a monolith with tightly coupled components
• Expect significant deltas during final sync
• App already scheduled for a maintenance window

Example Cutover Procedure (Shut-Down Approach)

1. Notify users of maintenance window
2. Freeze application changes
3. Stop application services on the on-prem server
4. Stop background jobs / schedulers
5. Perform final replication sync (AWS MGN, DMS, rsync, etc.)
6. Power off or isolate on-prem server
7. Launch AWS instance and test integrity
8. Run smoke tests
9. Update DNS to point to AWS system
10. Open application to users

Summary

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