BFD-3701: Update BFD Server load balancing to support Blue/Green Deployments

[malessi]

JIRA Ticket:
BFD-3701

What Does This PR Do?

This PR implements Blue/Green deployments by utilizing a Network Load Balancer with multiple Listeners each pointing to separate Target Groups. These Listeners listen on separate ports allowing traffic to "green" instances to only hit "green" and vice-versa.

Additionally, some defects with the existing Blue/Green ASG implementation have been fixed:

• Warm Pool management has been moved entirely to the null_resource.manage_warm_pool resource due to defects in the Terraform AWS Provider, specifically that the force_delete_warm_pool property is not respected and Terraform Warm Pool creation is sometimes inconsistent
• Only the green ASG's Launch Template version is updated to the latest version rather than both ASGs being updated

IMPORTANT: This PR cannot be merged until a strategy for resolving existing DNS entries is determined.

What Should Reviewers Watch For?

If you're reviewing this PR, please check for these things in particular:

What Security Implications Does This PR Have?

Please indicate if this PR does any of the following:

• Adds any new software dependencies

• Modifies any security controls

• Adds new transmission or storage of data

• Any other changes that could possibly affect security?

  • Introduction of new Network Load Balancer

• I have considered the above security implications as it relates to this PR. (If one or more of the above apply, it cannot be merged without the ISSO or team security engineer's (@sb-benohe) approval.)

Validation

Have you fully verified and tested these changes? Is the acceptance criteria met? Please provide reproducible testing instructions, code snippets, or screenshots as applicable.

• terraform applying server in 3701-test with simulated changes causing a new Launch Template version to be created (from version 10 -> 11, in this case), verifying that:
  • The odd ASG is chosen as green and, after scale-out, is attached to the green Target Group (reachable by port 7443)
  • The even ASG remains blue and remains attached to the blue Target Group (reachable by port 443)
  • odd's warm pool is created as expected
  • even's warm pool remains active with the appropriate number of instances
  • odds Launch Template version becomes 11
  • even's Launch Template version remains 10 (the last accepted version of BFD Server from the previous server apply cycle)
• Subsequently terraform applying server in 3701-test without further changes to the Launch Template (simulating green being accepted to blue), verifying that:
  • The odd ASG is chosen as blue and is immediately attached to the blue TG and detached from green
  • The even ASG is scaled-in to 0 and detached from the blue TG with its instances remaining for the 60 second deregistration (satisfying non-zero downtime deployment requirements)
  • odd's warm pool remains
  • even's warm pool is destroyed without any delay
• Running a local Locust Regression Suite, continuously, during the above terraform apply cycle against the blue TG (port 443 on the NLB), verifying that:
  • There were no errors (green -> blue swapover is invisible to clients)

[mjburling]

Thanks for trying to keep this as simple as possible. This looks really straightforward! 🥇