The answer is to add subnets from multiple Availability Zones to the Lambda VPC configuration. This resolves the timeout because a Lambda function deployed in a VPC requires subnets in at least two AZs to ensure high availability; with only one subnet, the function has no redundancy if that single AZ experiences an outage or if the subnet lacks a route to a NAT gateway for internet access, causing connection attempts to RDS to hang until the 30-second timeout. On the AWS Certified Solutions Architect Professional SAP-C02 exam, this scenario tests your understanding of Lambda VPC networking fundamentals and the common trap of assuming more memory or removing the VPC will fix connectivity issues—neither addresses the availability zone dependency. Remember the mnemonic: "Lambda needs two AZs to play, or your RDS calls will delay."
SAP-C02 Design for New Solutions Practice Question
This SAP-C02 practice question tests your understanding of design for new 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.
Network Topology
A company is troubleshooting a Lambda function that is timing out when trying to connect to an RDS database in a VPC. The Lambda function configuration is shown in the exhibit. The function has a timeout of 30 seconds and a memory size of 128 MB. The VPC has subnets in multiple Availability Zones, but the function only has one subnet configured. What change will MOST LIKELY resolve the timeout?
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
✓
Add subnets from other Availability Zones to the VPC configuration.
Lambda functions require subnets in multiple Availability Zones for high availability. With only one subnet, if that AZ becomes unavailable or the subnet lacks a NATgateway for internet access, the function may fail. Adding subnets from multiple AZs improves availability. Option B is correct. Option A is wrong because increasing memory may help performance but not connectivity. Option C is wrong because VPC is needed for RDS. Option D is wrong because the security group may be correct.
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.
✓
Add subnets from other Availability Zones to the VPC configuration.
Why this is correct
Multiple subnets improve availability and connectivity.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Remove the VPC configuration to allow the function to access the internet.
Why it's wrong here
Removing VPC will prevent access to RDS in VPC.
✗
Increase the function's memory size to 1024 MB.
Why it's wrong here
Memory increase may help compute, not network connectivity.
✗
Update the security group to allow all outbound traffic.
Why it's wrong here
Security group may already allow outbound.
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 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 SAP-C02 subnetting questions on CIDR, address ranges, and subnet selection.
Design for New Solutions — This question tests Design for New Solutions — CIDR notation defines the prefix length..
What is the correct answer to this question?
The correct answer is: Add subnets from other Availability Zones to the VPC configuration. — Lambda functions require subnets in multiple Availability Zones for high availability. With only one subnet, if that AZ becomes unavailable or the subnet lacks a NAT gateway for internet access, the function may fail. Adding subnets from multiple AZs improves availability. Option B is correct. Option A is wrong because increasing memory may help performance but not connectivity. Option C is wrong because VPC is needed for RDS. Option D is wrong because the security group may be correct.
What should I do if I get this SAP-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 SAP-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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