DBS-C01 Redis Cluster Mode Practice Question
A company runs a self-managed Redis cluster on Amazon EC2 for caching. The cluster has one primary and two replicas, each on c5.large instances. The application experiences high latency during peak hours. CloudWatch metrics show that the primary node's CPU utilization is consistently above 80% and the network bandwidth is near the instance limit. The replicas show moderate CPU usage. The team wants to reduce latency without increasing cost significantly. Which combination of actions should the team take? (Choose two.)
⚠ Common exam trap
Candidates may incorrectly select reading from replicas (option C) assuming it alleviates the primary's CPU, but the primary's high CPU is due to both CPU and network saturation from read/write operations; read replicas only offload read queries, not the underlying processing on the primary.
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
✓
Enable Redis Cluster Mode and distribute data across multiple shards.
Enables Redis Cluster Mode to shard data across multiple nodes, reducing CPU and network load on the primary. Option E migrates to Amazon ElastiCache for Redis with Cluster Mode, which manages scaling and reduces operational overhead. Together, they address the bottleneck without significant cost increase. Option C (read from replicas) does not reduce primary write/CPU load. Option D (upgrade instance) increases cost and may still hit network limits. Option B (add replicas) increases cost and does not reduce primary load.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Enable Redis Cluster Mode and distribute data across multiple shards.
Why this is correct
Correct. Enabling Redis Cluster Mode shards data across multiple nodes, reducing CPU and network load on the primary.
- ✗
Add more EC2 instances as additional replicas to offload reads.
Why it's wrong here
Incorrect. Adding more replicas increases cost but does not reduce the primary node's CPU or network load.
- ✗
Configure the application to read from replica nodes.
Why it's wrong here
Incorrect. Reading from replicas offloads read traffic but does not reduce the primary's CPU or network bottleneck for writes and general processing.
- ✗
Upgrade the primary to a c5.2xlarge instance type.
Why it's wrong here
Incorrect. Upgrading to a larger instance (vertical scaling) increases cost significantly and may still hit network limits; horizontal scaling is preferred.
- ✓
Migrate to Amazon ElastiCache for Redis with Cluster Mode enabled.
Why this is correct
Correct. Migrating to ElastiCache for Redis with Cluster Mode provides managed horizontal scaling and reduces operational burden.
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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JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This DBS-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 DBS-C01 exam.