Changing the AMI your instances use is like changing the foundation of your service while it keeps running. Done badly it means outages; done well it is nearly invisible to the user. The good news: there are proven patterns that make this migration safe and reversible.
The common basis is not to edit live instances, but to launch new instances with the new AMI and shift traffic in a controlled way.
Before migrating: prepare the ground
- Test the new AMI in a staging environment identical to production.
- Reliable health checks: define checks that confirm a new instance is genuinely healthy.
- Rollback plan: have the previous version and the procedure to return to it ready.
- Observability: metrics and alerts to spot regressions instantly.
Zero-downtime migration strategies
| Strategy | How it works | Ideal for |
|---|---|---|
| Rolling update | Replaces instances in batches, little by little | Services in an Auto Scaling Group |
| Blue/Green | You stand up a new environment and switch traffic at once | Migrations with instant rollback |
| Canary | You send a small percentage of traffic to the new version | Validating in production at low risk |
Three patterns for changing AMIs without interrupting the service.
Rolling update
You update the Launch Template with the new AMI and the Auto Scaling Group replaces instances in waves: it launches new ones, waits for them to pass the health check and retires the old ones. Simple and with no extra infrastructure, although both versions coexist for a while.
Blue/Green
You stand up a parallel environment (green) with the new AMI while the current one (blue) keeps serving. Once green is validated, you redirect traffic at the load balancer or in DNS. If anything fails, you are back on blue in seconds. It is the pattern with the fastest rollback, at the cost of temporarily duplicating resources.
Canary
You send a small fraction of traffic to instances with the new AMI and observe. If the metrics hold, you raise the percentage progressively up to 100 %. It minimises the blast radius of an unexpected problem.
After migrating
- Watch metrics and logs for a reasonable period before declaring the migration good.
- Mark the old AMI as deprecated so it is not relaunched by mistake.
- Document the deployed version and the reason for the change.
- Do not delete the previous image immediately: keep it in case you need a rollback.
Frequently asked questions
Which strategy is best for zero downtime?
Blue/Green offers the fastest rollback; rolling update is simpler and cheaper; canary minimises risk by validating in production. The choice depends on your risk tolerance and your infrastructure budget.
Do I need to duplicate the infrastructure to migrate?
Only with blue/green, and temporarily. With rolling update or canary you reuse the same group and replace instances as you go, without duplicating the whole environment.
How do I guarantee I can go back?
Keep the previous AMI and its Launch Template, define reliable health checks and have the rollback procedure tested before starting the migration.
At imaxe.cloud we version our images so that migrating between versions is predictable and reversible.
