ANS-C01 Network Implementation Practice Question
A company has deployed a web application behind an Application Load Balancer (ALB) in a VPC. The ALB is in public subnets, and the web servers are in private subnets. The ALB is configured with a target group pointing to the web servers. Users report intermittent 503 errors. The web servers are healthy according to the target group health checks. What is the most likely cause?
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 ALB subnets do not have a route to an internet gateway
An internet-facing ALB must be deployed in public subnets that have a route to an internet gateway. Since the web servers are healthy but users get intermittent 503 errors, the issue is likely that the ALB's subnets lack a route to an internet gateway, preventing the ALB from sending responses to clients. Option B is wrong because a long health check interval would not cause 503 errors if the targets are healthy. Option C is wrong because the ALB is described as being in public subnets and should be internet-facing; if it were internal, it would not receive internet traffic. Option D is wrong because cross-zone load balancing being disabled affects traffic distribution but does not cause intermittent 503 errors when targets are healthy.
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 ALB subnets do not have a route to an internet gateway
Why this is correct
Without a route to an internet gateway, the ALB cannot respond to client requests, causing 503 errors.
- ✗
The target group health check interval is too long
Why it's wrong here
Health checks are passing, so the interval is not the issue.
- ✗
The ALB is configured as internal instead of internet-facing
Why it's wrong here
If it were internal, users would not be able to reach it at all, not just intermittent errors.
- ✗
Cross-zone load balancing is disabled
Why it's wrong here
Disabling cross-zone load balancing could cause uneven distribution but not 503 errors.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This ANS-C01 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 ANS-C01 exam.