govuk-aws: 26. Remove load balancer tier
We currently have a dedicated tier of load balancers for the backend, frontend and api VDCs. In the Amazon world these are less useful as we also have ELBs in place to handle the autoscaling of instances. We want to reduce the networking complexity and remove these machines.
We will not change the current vcloud based platforms.
In the AWS environment we will remove the load balancer hosts / ELBs and instead add external ELBs to a number of other autoscaling groups (such as the frontend / backend hosts themselves) to make them directly available, but security group restricted.
We have also decided to split the domains we use to an internal and external one. That is discussed in ADR TODO: TBC.
3 classes of machines, and the instances running them, will be removed from our architecture in this environment. Some of the LBs processing, such as trace ids, will be pushed down the stack to the application servers themselves. We will have more ELBs running for a period of time.
All traffic will go to the external domain names at this phase of the move. The ADR TODO: TBC will explain the risks and remediations for this change.