The answer is to configure the ECS service to use multiple subnets with larger CIDR blocks across multiple Availability Zones. This is the most resilient solution because ECS Fargate tasks require a unique, private IP address from the VPC subnet to launch, and an IP shortage occurs when the subnet’s address pool is exhausted. By expanding the CIDR block, you increase the total IP capacity, and by distributing tasks across multiple subnets in different AZs, you avoid a single point of failure and spread the IP demand. On the DOP-C02 exam, this question tests your understanding of VPC networking fundamentals for Fargate, often hiding traps like increasing the desired count (which worsens the shortage) or misattributing the issue to IAM roles or VPC endpoints. A common memory tip is to think of subnets as parking lots: if your lot is full, you either need a bigger lot (larger CIDR) or more lots in different locations (multiple AZs).
DOP-C02 Resilient Cloud Solutions Practice Question
This DOP-C02 practice question tests your understanding of resilient cloud solutions. 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 application on Amazon ECS with Fargate launch type. The application experiences intermittent failures when the ECS service scheduler attempts to place tasks during a deployment. The DevOps engineer notices that tasks fail to start due to insufficient IP addresses in the VPC subnets. What is the MOST resilient solution to prevent this issue?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Configure the ECS service to use multiple subnets with larger CIDR blocks across multiple Availability Zones.
Option D is correct because using a larger CIDR block for subnets provides more IP addresses, and using multiple subnets across Availability Zones increases availability and capacity. Option A is wrong because increasing desired count does not solve IP shortage. Option B is wrong because ECS service-linked role does not affect IP allocation. Option C is wrong because VPC endpoints do not provide IP addresses for tasks.
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.
✗
Create an ECS service-linked role with permissions to allocate IPs.
Why it's wrong here
Role permissions are not the cause of IP shortage.
✗
Increase the desired task count in the ECS service to pre-warm IP addresses.
Why it's wrong here
Pre-warming does not work; tasks consume IPs only when running.
✗
Use VPC endpoints for ECS to reduce IP usage.
Why it's wrong here
VPC endpoints do not reduce IP consumption for tasks.
✓
Configure the ECS service to use multiple subnets with larger CIDR blocks across multiple Availability Zones.
Why this is correct
More subnets and larger CIDRs increase available IPs and resilience.
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 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 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.
Resilient Cloud Solutions — This question tests Resilient Cloud Solutions — CIDR notation defines the prefix length..
What is the correct answer to this question?
The correct answer is: Configure the ECS service to use multiple subnets with larger CIDR blocks across multiple Availability Zones. — Option D is correct because using a larger CIDR block for subnets provides more IP addresses, and using multiple subnets across Availability Zones increases availability and capacity. Option A is wrong because increasing desired count does not solve IP shortage. Option B is wrong because ECS service-linked role does not affect IP allocation. Option C is wrong because VPC endpoints do not provide IP addresses for tasks.
What should I do if I get this DOP-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 DOP-C02 subnetting questions on CIDR, address ranges, and subnet selection.
What is the key concept behind this question?
CIDR notation defines the prefix length.
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Question Discussion
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