Your team starts to maintain a new application in AWS that uses a blue/green deployment. All these AWS services are deployed in a CloudFormation stack. The application has an ELB and two Auto Scaling Groups for the current release and the new release. After the new ASG is attached to the ELB, there are tests to ensure that the new code has run smoothly. However, there are possibilities that the tests have failed. You need to use a script to implement this blue/green deployment. Which of the below options would you consider to recover the system when the tests fail?

Answer options:

A.Use SNS to send a notification to your team to react to the failure in time.
B.Collect logs and send them to AWS CloudWatch Logs which can help in troubleshooting the failure.
C.Raise a CloudWatch alarm to alert the team when there is a failure. Also, create a CloudWatch dashboard based on the Auto Scaling Group metrics.
D.Roll back the system to the original state by detaching the new ASG from ELB and attaching the old ASG in ELB.

Correct Answer – D
For any script or code that manipulates the AWS resources, a key concept is that it should be auto-healing and be able to recover the system to the original status if anything goes wrong. In other words, the script should be robust enough to ensure that the system can roll back automatically when an exception happens.
Option A is incorrect: SNS definitely helps as a notification method. However, it does not help roll back the system so that it is not the most important thing to consider.
Option B is incorrect: Normally, the application should already generate troubleshooting logs. In this question, it is not required to send logs to CloudWatch Logs.
Option C is incorrect: Similar reason as
Option A. This option can be regarded as a supplement.
Option D is CORRECT: Because after detaching the new ASG and attaching the old ASG, the system is rolled back to the previous state. This is the most important step to recover the system when a rollback is required.