DVA-C02 Development with AWS Services Practice Question
A company is using AWS Lambda functions behind an Amazon API Gateway REST API. Users report intermittent 503 errors. The Lambda function code appears correct. Which action is MOST likely to resolve the issue?
⚠ Common exam trap
A common mix-up: candidates confuse API Gateway throttling limits (which return 429 errors) with Lambda concurrency limits (which return 503 errors), leading them to incorrectly choose option D.
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
✓
Request a service quota increase for Lambda concurrent executions.
Intermittent 503 errors from API Gateway often indicate that Lambda concurrent execution limits have been reached. When the number of simultaneous invocations exceeds the account-level or function-level reserved concurrency, API Gateway returns a 503 'Service Unavailable' response. Increasing the Lambda concurrent executions quota allows more invocations to be processed without throttling.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Increase the Lambda function memory allocation.
Why it's wrong here
Increasing the Lambda function's memory allocation primarily impacts its CPU power and overall execution duration for a single invocation. While more memory can improve the performance and reduce the execution time of individual function calls, it does not directly address or increase the number of concurrent invocations that Lambda can process simultaneously. Exceeding the account-level or function-level concurrency quota will still result in throttling, regardless of individual function memory settings.
- ✗
Increase the Lambda function timeout.
Why it's wrong here
Increasing the Lambda function timeout setting addresses scenarios where individual function invocations exceed their allotted execution duration, leading to a 504 Gateway Timeout error if invoked via API Gateway. This parameter does not influence the number of concurrent executions Lambda can handle. A 503 Service Unavailable error specifically indicates that the Lambda service itself is unable to process the request due to resource constraints, typically concurrency limits, not an individual function's execution time.
- ✓
Request a service quota increase for Lambda concurrent executions.
Why this is correct
A 503 Service Unavailable error from Lambda indicates that the service is currently unable to handle the request, most commonly because the account's or function's concurrent execution quota has been reached. Each AWS account has a default regional concurrency limit for Lambda functions, and exceeding this limit causes subsequent invocation attempts to be throttled. Requesting a service quota increase directly addresses this bottleneck, allowing more Lambda instances to run in parallel and process incoming API Gateway requests.
- ✗
Increase the API Gateway throttling limits.
Why it's wrong here
Increasing API Gateway throttling limits controls the maximum number of requests per second and burst capacity that API Gateway will accept before rejecting requests. When API Gateway itself throttles requests, it returns a 429 Too Many Requests error to the client, indicating that the client has exceeded the API's rate limits. This is distinct from a 503 error originating from the backend Lambda function, which signifies that Lambda's own concurrency limits have been hit.
Visual reference
Quick reference
Cloud Service Model Comparison
| Model | You Manage | Provider Manages | Examples |
|---|---|---|---|
| IaaS | OS, runtime, apps, data | Hardware, hypervisor, networking | EC2, Azure VMs, GCP Compute Engine |
| PaaS | Apps and data | OS, runtime, middleware, hardware | Elastic Beanstalk, Azure App Service |
| SaaS | Data and settings only | Everything else | Microsoft 365, Salesforce, Workday |
| FaaS / Serverless | Function code only | Infra, scaling, runtime | Lambda, Azure Functions, Cloud Run |
| CaaS | Containers and apps | Kubernetes, OS, hardware | EKS, AKS, GKE |
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This DVA-C02 practice question is part of Courseiva's free Amazon Web Services certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the DVA-C02 exam.