AWS Migrate Classic Load Balancer to Application Load Balancer

Question

I am looking for integrating WAF in my existing server setup, since I have Classic Load Balancer (with EC2 instances) which does not support WAF I need to migrate to Application Load Balancer.

Is it possible to migrate the existing Classic Load Balancer to Application Load Balancer without changing the DNS (A Record)?

Answer 1

You cannot migrate from CLB to ALB using any tools that I am aware of. You can create the ALB to run in parallel with the CLB. Once you are confident that the ALB is working correctly with you WAF configuration, change the Route 53 records. Wait a few days and then delete the CLB. This will allow the DNS servers around the world to catch up with the new DNS settings. The one area that you will have problems running the new ELB in parallel is if you are using SSL offload on the ELB. This will require the DNS switch over so that the DNS name matches the SSL records. For this, I usually add a "test.mydomain.com" record to verify that SSL is working.

Answer 2

Amazon released a migration tool to make it easy to migrate Classic Load Balancer to an Application Load Balancer. They provide instructions on how you can do the migration side-by-side, with a strategy for gradually directing traffic over to the new ALB. For details, see https://docs.aws.amazon.com/elasticloadbalancing/latest/userguide/migrate-to-application-load-balancer.html