The answer is that the task definition JSON is missing the requiresCompatibilities field set to ["FARGATE"]. This is the most likely cause because when using Amazon ECS with Fargate, the task definition must explicitly declare its compatibility through the requiresCompatibilities attribute; without it, the service cannot validate the launch type, causing the deploy stage to fail intermittently when a new revision is created. On the AWS Certified DevOps Engineer Professional DOP-C02 exam, this tests your understanding of ECS task definition structure and the specific requirements for Fargate versus EC2 launch types—a common trap is assuming Fargate is inferred from other settings like network mode or execution role. Remember the mnemonic: "FARGATE requires explicit compatibility; if it's missing, your deployment is missing."
DOP-C02 SDLC Automation Practice Question
This DOP-C02 practice question tests your understanding of sdlc automation. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
You are a DevOps engineer for a company that uses AWS CodePipeline to deploy a microservice to Amazon ECS with Fargate. The pipeline has a source stage (CodeCommit), a build stage (CodeBuild) that builds a Docker image and pushes it to Amazon ECR, and a deploy stage that uses an ECS task definition update. Recently, the deploy stage started failing intermittently with the error 'The task definition does not have a compatibilities attribute set correctly.' The task definition is generated dynamically during the build stage and uses the 'FARGATE' launch type. The error occurs only when a new task definition revision is created. You suspect the issue is related to how the task definition is generated. Upon reviewing the buildspec, you see that the task definition JSON is created using environment variables for the image URI. What is the MOST likely cause and solution?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "most likely"
Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The task definition JSON does not include the 'requiresCompatibilities' field with the value '["FARGATE"]'.
Option B is correct because the 'requiresCompatibilities' attribute must be explicitly set to 'FARGATE' for Fargate tasks. Option A is incorrect because the error is about compatibilities, not execution role. Option C is incorrect because network mode should be 'awsvpc', but that is not the error. Option D is incorrect because CPU and memory values are required but would cause a different error.
Key principle: NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✗
The task definition is missing the 'executionRoleArn' field, which is required for Fargate.
Why it's wrong here
Missing execution role causes a different error about permissions.
✓
The task definition JSON does not include the 'requiresCompatibilities' field with the value '["FARGATE"]'.
Why this is correct
Without this field, ECS cannot determine the launch type compatibility.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Static NAT maps one inside address to one outside address.
✗
The task definition specifies 'networkMode' as 'bridge', but Fargate requires 'awsvpc'.
Why it's wrong here
Incorrect network mode causes a different error.
✗
The task definition does not specify 'cpu' and 'memory' values, which are required for Fargate.
Why it's wrong here
Missing cpu/memory causes a validation error, not a compatibilities error.
Common exam traps
Common exam trap: NAT rules depend on direction and matching traffic
NAT is not only about the public address. The inside/outside interface roles and the ACL or rule that matches traffic are just as important.
Detailed technical explanation
How to think about this question
NAT questions usually test address translation, overload/PAT behaviour, static mappings and whether the right traffic is being translated. Read the interface direction and address terms carefully.
KKey Concepts to Remember
Static NAT maps one inside address to one outside address.
PAT allows many inside hosts to share one public address using ports.
Inside local and inside global describe the private and translated addresses.
NAT ACLs identify traffic for translation, not always security filtering.
TExam Day Tips
→Identify inside and outside interfaces first.
→Check whether the scenario needs static NAT, dynamic NAT or PAT.
→Do not confuse NAT matching ACLs with normal packet-filtering intent.
Key takeaway
NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.
Real-world example
How this comes up in practice
A company's IT admin needs to give a contractor read-only access to production logs without sharing account credentials. Using role-based access control (RBAC) and temporary scoped permissions — not a permanent shared password — is the correct pattern. Questions like this test whether you can apply least-privilege access across cloud identity services.
What to study next
Got this wrong? Here's your next step.
Review the four NAT address types (inside local, inside global, outside local, outside global), PAT port overload, and static vs dynamic NAT use cases. Then practise related DOP-C02 NAT questions on configuration and troubleshooting.
SDLC Automation — This question tests SDLC Automation — Static NAT maps one inside address to one outside address..
What is the correct answer to this question?
The correct answer is: The task definition JSON does not include the 'requiresCompatibilities' field with the value '["FARGATE"]'. — Option B is correct because the 'requiresCompatibilities' attribute must be explicitly set to 'FARGATE' for Fargate tasks. Option A is incorrect because the error is about compatibilities, not execution role. Option C is incorrect because network mode should be 'awsvpc', but that is not the error. Option D is incorrect because CPU and memory values are required but would cause a different error.
What should I do if I get this DOP-C02 question wrong?
Review the four NAT address types (inside local, inside global, outside local, outside global), PAT port overload, and static vs dynamic NAT use cases. Then practise related DOP-C02 NAT questions on configuration and troubleshooting.
Are there clue words in this question I should notice?
Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
What is the key concept behind this question?
Static NAT maps one inside address to one outside address.
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