Managing and Deploying Complex Applications with AWS OpsWorks

Answer - D and E.

Option A is incorrect because you would have to re-launch new instances to change the AMI, and you can't do that with chef recipes only.

Option B is incorrect because the AMI replacements should be done without incurring application downtime or capacity problems.

So if you shutdown the stack, all applications will be stopped.

Option C is incorrect because the application could face the problem of insufficient capacity.

Option D is CORRECT because it represents a common practice of Blue-Green Deployment which is carried out for reducing the downtime and risk by running two identical production environments called Blue and Green.

Please see the "More information.." section for additional details.

Option E is CORRECT because you can only add new instances at the layer level by specifying to use Custom AMI at the stack level.

More information on Blue-Green Deployment:

Blue-green deployment is a technique that reduces downtime and risk by running two identical production environments called Blue and Green.

At any time, only one of the environments is live, with the live environment serving all production traffic.

For this example, Blue is currently live, and Green is idle.

As you prepare a new version of your software, deployment and the final stage of testing takes place in an environment that is not live: in this example, Green.

Once you have deployed and fully tested the software in Green, you switch the router.

So all incoming requests now go to Green instead of Blue.

Green is now live, and Blue is idle.

This technique can eliminate downtime due to application deployment.

In addition, blue-green deployment reduces risk: if something unexpected happens with your new version on Green, you can immediately roll back to the last version by switching back to Blue.

Please refer to the below URL for more details.

https://d0.awsstatic.com/whitepapers/AWS_Blue_Green_Deployments.pdf

Sure, I'd be happy to provide a detailed explanation of each answer choice and how it relates to the scenario described.

A. Assign a custom recipe to each layer that replaces the underlying AMI. Use OpsWorks life-cycle events to incrementally execute this custom recipe and update the instances with the new AMI.

This answer suggests using a custom recipe to replace the underlying Amazon Machine Image (AMI) for each layer of the OpsWorks stack. The OpsWorks life-cycle events would be used to incrementally execute this custom recipe, meaning that each instance in the layer would be updated with the new AMI one at a time. This approach would minimize the risk of downtime, as only one instance would be updated at a time. Additionally, by using a custom recipe, you can ensure that each instance is updated in a consistent manner, which can help prevent configuration drift.

B. Specify the latest AMI in the custom AMI at the stack level. Terminate instances of the stack and let OpsWork launch new instances with the new AMI.

This answer suggests specifying the latest AMI in the custom AMI at the stack level. Once this is done, you would terminate the instances of the stack and let OpsWorks launch new instances with the new AMI. This approach would result in downtime, as all instances would need to be terminated and replaced with new instances. However, this approach would be simpler than some of the other options, as you would not need to worry about updating instances one at a time.

C. Identify all EC2 instances of your OpsWork stack, stop each instance, replace the AMI ID property with the latest AMI ID, and restart the instance. To avoid downtime, make sure no more than one instance is stopped at the same time.

This answer suggests identifying all EC2 instances of your OpsWorks stack and updating each instance's AMI ID property with the latest AMI ID. To avoid downtime, you would need to stop each instance and restart it after the update. To minimize the risk of downtime, you would need to make sure that no more than one instance is stopped at the same time. This approach would be more labor-intensive than some of the other options, as you would need to manually update each instance's AMI ID property.

D. Create a new stack and layers with identical configuration, add instances with the latest AMI specified as a custom AMI to the new layers, switch DNS to the new stack, and tear down the old stack.

This answer suggests creating a new stack and layers with identical configuration to the existing stack. Once the new stack is created, you would add instances with the latest AMI specified as a custom AMI to the new layers. Once the new instances are up and running, you would switch DNS to the new stack and tear down the old stack. This approach would result in downtime during the DNS switch, but it would also ensure that all instances are updated to the latest AMI in a consistent manner.

E. Add new instances with the latest AMI as a custom AMI to all OpsWork layers of your stack and terminate the old ones.

This answer suggests adding new instances with the latest AMI as a custom AMI to all OpsWork layers of your stack. Once the new instances are up and running, you would terminate the old ones. This approach would result in downtime during the instance termination, but it would ensure that all instances are updated to the latest AMI in a consistent manner.

In summary, each answer choice represents a different approach to updating the Amazon Machine Images (AMIs) for an OpsWorks stack. Option A and E involve updating instances one at a time to minimize downtime, while options B, C, and D involve more drastic measures that may result in downtime but are simpler to execute. The