[CodeDeploy] [ECS B/G Taskset Health Check ]: ECS/CodeDeploy B/G Replacement Taskset health check

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**Tell us about your request**
ECS has been integerated with CodeDeploy to perform blue/green deployments. However, the replacement taskset is not correctly communicating the taskset health to CodeDeploy, resulting in successful deployments for unhealthy tasks,

**Which service(s) is this request for?**
Fargate, ECS

**Tell us about the problem you're trying to solve. What are you trying to do, and why is it hard?**
What outcome are you trying to achieve, ultimately, and why is it hard/impossible to do right now? What is the impact of not having this problem solved? The more details you can provide, the better we'll be able to understand and solve the problem.

Problem: CD deployments successfully complete when replacement taskset is unhealthy and should fail.
Impact: Traffic is shifted to unhealthy taskset leading to downtime.

**Are you currently working around this issue?**
How are you currently solving this problem?
The current workaround is to implement a BeforeAllowTraffic hook script in the CD deployment to manually check health of taskset before traffic is shifted.

**Additional context**
Anything else we should know?

**Attachments**
If you think you might have additional information that you'd like to include via an attachment, please do - we'll take a look. (Remember to remove any personally-identifiable information.)

No repository files or tests are named. Start by reviewing the ECS/CodeDeploy blue/green deployment behavior and the BeforeAllowTraffic hook workaround described in the issue. Done means unhealthy replacement tasksets prevent deployment completion before traffic is shifted.

Written by the indexing model from the issue text.