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Question 191 of 1,740

SDLC Automation →hardMultiple ChoiceObjective-mapped

Quick Answer

The answer is the security group for the ElastiCache cluster only allows inbound traffic from the security group of the original task set, not the new task set created during the blue/green deployment. In an ECS blue/green deployment using the CODE_DEPLOY controller, the new task set is provisioned with its own distinct security group, separate from the original task set. If the ElastiCache security group ingress rule is scoped to the original task set’s security group ID, the new task set’s traffic is implicitly denied, causing the connection failure and subsequent health check rollback. This scenario tests your understanding of how security group dependencies must be explicitly updated during blue/green deployments, a common trap on the DOP-C02 exam where candidates mistakenly assume the same security group applies to both task sets. A key memory tip is to think of blue/green as creating a completely separate network identity for the new environment—just as you would update an ALB target group, you must also update any downstream security group rules to include the new task set’s security group.

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.

A company runs a containerized microservices application on Amazon ECS with Fargate. The application is deployed using AWS CodePipeline with CodeBuild as the build stage and ECS as the deploy stage. The pipeline uses a deployment controller of type CODE_DEPLOY with a blue/green deployment strategy. Recently, the team noticed that during deployments, the new task set fails health checks and the deployment is rolled back. The application logs indicate that the new containers fail because they cannot connect to the Redis cluster, which is a required dependency. The Redis cluster is running on Amazon ElastiCache and is in the same VPC as the ECS tasks. The team has verified that the security group for the ElastiCache cluster allows inbound traffic from the ECS tasks' security group. The ECS task definition includes the Redis endpoint as an environment variable. What is the MOST likely cause of the connection failure?

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.

Question 1hardmultiple choice

Full question →

A
The new task set is being launched in different private subnets that do not have a route to the ElastiCache cluster.
Why wrong: ECS Fargate tasks in the same VPC and subnets should have network connectivity; the subnets are likely the same.
B
The Redis endpoint environment variable is not being passed correctly to the new task set because of a misconfiguration in the task definition.
Why wrong: Environment variables are passed correctly if the task definition is updated; the issue is connectivity, not variable passing.
C
The security group for the ElastiCache cluster only allows inbound traffic from the security group of the original task set, not the new task set created during deployment.
During a blue/green deployment, the new task set uses a different security group (or the same group but with a new rule) and the ElastiCache security group must be updated to allow traffic from the new tasks.
D
The new task set is using a different VPC than the ElastiCache cluster.
Why wrong: The deployment uses the same VPC; otherwise, the original tasks would also fail.

Full breakdown with real-world context →

Answer choices

Why each option matters

Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.

Correct answer & explanation

✓

The security group for the ElastiCache cluster only allows inbound traffic from the security group of the original task set, not the new task set created during deployment.

Option B is correct because in a blue/green deployment with CODE_DEPLOY, the new task set is created in a separate target group, and the security group for the ElastiCache cluster must allow traffic from the new task set's security group. If the security group rule is only attached to the original task set's security group, the new task set cannot connect. Option A is wrong because the ECS service uses the same subnets; the issue is not subnet-related. Option C is wrong because if the environment variable is correctly set, DNS resolution should work. Option D is wrong because the security group for ECS tasks is typically attached to the service, and adding a new security group rule is necessary.

Key principle: Count usable hosts — not total addresses — and remember that the network and broadcast addresses are not available to hosts in standard IPv4 subnets.

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 new task set is being launched in different private subnets that do not have a route to the ElastiCache cluster.
Why it's wrong here
ECS Fargate tasks in the same VPC and subnets should have network connectivity; the subnets are likely the same.
✗
The Redis endpoint environment variable is not being passed correctly to the new task set because of a misconfiguration in the task definition.
Why it's wrong here
Environment variables are passed correctly if the task definition is updated; the issue is connectivity, not variable passing.
✓
The security group for the ElastiCache cluster only allows inbound traffic from the security group of the original task set, not the new task set created during deployment.
Why this is correct
During a blue/green deployment, the new task set uses a different security group (or the same group but with a new rule) and the ElastiCache security group must be updated to allow traffic from the new tasks.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
CIDR notation defines the prefix length.
✗
The new task set is using a different VPC than the ElastiCache cluster.
Why it's wrong here
The deployment uses the same VPC; otherwise, the original tasks would also fail.

Common exam traps

Common exam trap: usable hosts are not the same as total addresses

Subnetting questions often tempt you into counting all addresses. In normal IPv4 subnets, the network and broadcast addresses are not usable host addresses.

Detailed technical explanation

How to think about this question

Subnetting questions test whether you can identify the network, broadcast address, usable range, mask and correct subnet. Slow down enough to calculate the block size correctly.

KKey Concepts to Remember

CIDR notation defines the prefix length.
Block size helps identify subnet boundaries.
Network and broadcast addresses are not usable hosts in normal IPv4 subnets.
The required host count determines the smallest suitable subnet.

TExam Day Tips

Write the block size before choosing the subnet.
Check whether the question asks for hosts, subnets or a specific address range.
Do not confuse /24, /25, /26 and /27 host counts.

Key takeaway

Count usable hosts — not total addresses — and remember that the network and broadcast addresses are not available to hosts in standard IPv4 subnets.

Real-world example

How this comes up in practice

A healthcare organisation deploys an application with a public-facing web tier and a private database tier. The database subnet has no public IP and only accepts connections from the web tier's security group. Questions like this test whether you can design cloud network isolation using VNets/VPCs, subnets, and security group rules.

What to study next

Got this wrong? Here's your next step.

Review block sizes, usable host formulas (2^n − 2), and how to find network and broadcast addresses for /24 through /30. Then practise related DOP-C02 subnetting questions on CIDR, address ranges, and subnet selection.

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FAQ

Questions learners often ask

What does this DOP-C02 question test?

SDLC Automation — This question tests SDLC Automation — CIDR notation defines the prefix length..

What is the correct answer to this question?

The correct answer is: The security group for the ElastiCache cluster only allows inbound traffic from the security group of the original task set, not the new task set created during deployment. — Option B is correct because in a blue/green deployment with CODE_DEPLOY, the new task set is created in a separate target group, and the security group for the ElastiCache cluster must allow traffic from the new task set's security group. If the security group rule is only attached to the original task set's security group, the new task set cannot connect. Option A is wrong because the ECS service uses the same subnets; the issue is not subnet-related. Option C is wrong because if the environment variable is correctly set, DNS resolution should work. Option D is wrong because the security group for ECS tasks is typically attached to the service, and adding a new security group rule is necessary.

What should I do if I get this DOP-C02 question wrong?

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?

CIDR notation defines the prefix length.

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