DVA-C02 Development with AWS Services Practice Question
This DVA-C02 practice question tests your understanding of development with aws services. 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 microservices application on Amazon ECS with Fargate. Each service has its own task definition and uses service discovery via AWS Cloud Map. Recently, one service is failing to connect to another service using the service discovery endpoint. The developer verified that both services are running and the security groups allow traffic. What is the most likely cause of the connectivity issue?
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 service discovery namespace is of type private but the DNS records are not being created.
Service discovery namespace must be of type 'private' for ECS tasks to resolve. Option C identifies this. Option A is incorrect because Fargate tasks use awsvpc network mode by default. Option B is incorrect because ECS service discovery works within VPC. Option D is incorrect because Cloud Map does not require an internet gateway for private namespaces.
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 service discovery namespace is of type private but the DNS records are not being created.
Why this is correct
If DNS records are missing, service discovery fails.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
The task definitions are not using the awsvpc network mode.
Why it's wrong here
Fargate tasks require awsvpc mode and it's default.
✗
The service discovery namespace is of type public and the services are in a private subnet.
Why it's wrong here
Public namespace would not resolve within VPC.
✗
The VPC does not have an internet gateway attached.
Why it's wrong here
Private namespace resolution does not require internet gateway.
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 DVA-C02 subnetting questions on CIDR, address ranges, and subnet selection.
Development with AWS Services — This question tests Development with AWS Services — CIDR notation defines the prefix length..
What is the correct answer to this question?
The correct answer is: The service discovery namespace is of type private but the DNS records are not being created. — Service discovery namespace must be of type 'private' for ECS tasks to resolve. Option C identifies this. Option A is incorrect because Fargate tasks use awsvpc network mode by default. Option B is incorrect because ECS service discovery works within VPC. Option D is incorrect because Cloud Map does not require an internet gateway for private namespaces.
What should I do if I get this DVA-C02 question wrong?
Review block sizes, usable host formulas (2^n − 2), and how to find network and broadcast addresses for /24 through /30. Then practise related DVA-C02 subnetting questions on CIDR, address ranges, and subnet selection.
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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Question Discussion
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