- Amazon ELB automatically distributes incoming application traffic across multiple Amazon EC2 instances in Multiple Availability Zones. Amazon EC2 regions have different levels of AZ's, US-East EC2 region has 5 AZ's and Singapore has 2 AZ's. When you are migrating the ELB make sure your configuration matches the levels of target Amazon EC2 region Availability zones .
- When Amazon ELB is created on target Amazon EC2 region, the ELB endpoint will be different from the source one. This has to be re configured on your Route 53 and other thick clients during migration.
- Since the ELB end point is different, if you had raised any pre-warming request to AWS support , please raise it again for the target region with new ELB end point. This is valid in use cases where you are moving the traffic from primary region to target region in event of outage.
- SSL certificates associated on the old Elastic Load Balancing service (source regions) need to be re configured to the new Elastic Load Balancing service in the Target region.
- Security Groups are region specific and has to be migrated/recreated in the target region. Make sure the security groups of ELB in target region matches the source region
- Amazon ELB is not an isolated service and usually it will be used in production with Amazon EC2, Auto Scaling group and Cloud Watch Alarms. In addition there will be health checks, time outs, thresholds etc configured specifically for an application in Amazon ELB. You need to ensure that all these items associated with Amazon ELB are transferred target region for proper functioning of the application. Using Amazon CloudFormation templates for creating infrastructure properties will surely help and ease the efforts involved during such ELB migration.
- To load balance your EC2 instances launched in default VPC, you have to create your load balancers within your default VPC. When you create a load balancer within default VPC, Elastic Load Balancing automatically creates a security group by defining the ports specified for the load balancer to be opened. Default VPC is currently not available in US-East. In case your Source region is US-West and you are planning your DR or migration with Target region as US-East, you need to be aware of this situation.
- In case Amazon ELB and Internal ELB are used inside Amazon VPC, you should ensure that the IP address ranges being used in source and target regions matches and aligns properly, so that routing and load balancing continues to work after migration.
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