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Question 178 - DOP-C02 discussion

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A company needs to implement failover for its application. The application includes an Amazon CloudFront distribution and a public Application Load Balancer (ALB) in an AWS Region. The company has configured the ALB as the default origin for the distribution.

After some recent application outages, the company wants a zero-second RTO. The company deploys the application to a secondary Region in a warm standby configuration. A DevOps engineer needs to automate the failover of the application to the secondary Region so that HTTP GET requests meet the desired RTO.

Which solution will meet these requirements?

A.
Create a second CloudFront distribution that has the secondary ALB as the default origin. Create Amazon Route 53 alias records that have a failover policy and Evaluate Target Health set to Yes for both CloudFront distributions. Update the application to use the new record set.
Answers
A.
Create a second CloudFront distribution that has the secondary ALB as the default origin. Create Amazon Route 53 alias records that have a failover policy and Evaluate Target Health set to Yes for both CloudFront distributions. Update the application to use the new record set.
B.
Create a new origin on the distribution for the secondary ALB. Create a new origin group. Set the original ALB as the primary origin. Configure the origin group to fail over for HTTP 5xx status codes. Update the default behavior to use the origin group.
Answers
B.
Create a new origin on the distribution for the secondary ALB. Create a new origin group. Set the original ALB as the primary origin. Configure the origin group to fail over for HTTP 5xx status codes. Update the default behavior to use the origin group.
C.
Create Amazon Route 53 alias records that have a failover policy and Evaluate Target Health set to Yes for both ALBs. Set the TTL of both records to 0. Update the distribution's origin to use the new record set.
Answers
C.
Create Amazon Route 53 alias records that have a failover policy and Evaluate Target Health set to Yes for both ALBs. Set the TTL of both records to 0. Update the distribution's origin to use the new record set.
D.
Create a CloudFront function that detects HTTP 5xx status codes. Configure the function to return a 307 Temporary Redirect error response to the secondary ALB if the function detects 5xx status codes. Update the distribution's default behavior to send origin responses to the function.
Answers
D.
Create a CloudFront function that detects HTTP 5xx status codes. Configure the function to return a 307 Temporary Redirect error response to the secondary ALB if the function detects 5xx status codes. Update the distribution's default behavior to send origin responses to the function.
Suggested answer: B

Explanation:

The best solution to implement failover for the application is to use CloudFront origin groups.Origin groups allow CloudFront to automatically switch to a secondary origin when the primary origin is unavailable or returns specific HTTP status codes that indicate a failure1. This way, CloudFront can serve the requests from the secondary ALB in the secondary Region without any delay or redirection. To set up origin groups, the DevOps engineer needs to create a new origin on the distribution for the secondary ALB, create a new origin group with the original ALB as the primary origin and the secondary ALB as the secondary origin, and configure the origin group to fail over for HTTP 5xx status codes.Then, the DevOps engineer needs to update the default behavior to use the origin group instead of the single origin2.

The other options are not as effective or efficient as the solution in option B. Option A is not suitable because creating a second CloudFront distribution will increase the complexity and cost of the application. Moreover, using Route 53 alias records with a failover policy will introduce some delay in detecting and switching to the secondary CloudFront distribution, which may not meet the zero-second RTO requirement.Option C is not feasible because CloudFront does not support using Route 53 alias records as origins3. Option D is not advisable because using a CloudFront function to redirect the requests to the secondary ALB will add an extra round-trip and latency to the failover process, which may also not meet the zero-second RTO requirement.

1: Optimizing high availability with CloudFront origin failover - Amazon CloudFront

2: Creating an origin group - Amazon CloudFront

3: Values That You Specify When You Create or Update a Web Distribution - Amazon CloudFront

asked 16/09/2024
Federico Miliacca
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