The answer is to enable cluster mode for the Redis cluster and add more shards. This is correct because cluster mode horizontally partitions data across multiple shards, each with its own primary and replica nodes, directly distributing the CPU and memory load that was causing 100% utilization during traffic spikes. By scaling out shards rather than vertically scaling a single node, you achieve linear scalability, allowing the cluster to handle increased concurrent requests without performance degradation, while the existing Auto Scaling group handles compute capacity separately. On the AWS Certified Solutions Architect Professional SAP-C02 exam, this scenario tests your understanding of when to use Redis cluster mode versus vertical scaling or read replicas; a common trap is choosing to simply increase instance size or add read replicas, which only addresses memory or read-heavy workloads, not the CPU bottleneck from write-heavy session state. Remember the mnemonic “Shards for CPU, Replicas for reads” to quickly differentiate horizontal partitioning from read scaling.
SAP-C02 Continuous Improvement for Existing Solutions Practice Question
This SAP-C02 practice question tests your understanding of continuous improvement for existing solutions. Examine the command output carefully: the correct answer depends on what the output actually shows, not on general recall alone. 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 critical web application on Amazon EC2 instances in an Auto Scaling group behind an Application Load Balancer (ALB). The application stores session state in an Amazon ElastiCache for Redis cluster. Recently, the operations team noticed that during traffic spikes, the ALB returns 5xx errors and the application becomes slow. CloudWatch metrics show that the Redis cluster's CPU utilization reaches 100% and memory usage is high. The Auto Scaling group scales out, but the new instances take several minutes to warm up and become healthy. The company needs to improve the application's ability to handle traffic spikes with minimal impact on performance. Which solution should the company implement?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Enable cluster mode for the Redis cluster and add more shards.
Enabling cluster mode for the Redis cluster and adding more shards horizontally partitions the data across multiple nodes, distributing both CPU and memory load. This directly addresses the 100% CPU and high memory utilization during traffic spikes, allowing the cluster to handle more concurrent requests without performance degradation. Cluster mode also provides linear scalability, which is essential for a critical web application experiencing variable traffic.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✗
Configure ElastiCache Auto Scaling to automatically add nodes when CPU utilization exceeds 75%.
Why it's wrong here
ElastiCache does not support automatic scaling based on CPU; scaling is manual.
✓
Enable cluster mode for the Redis cluster and add more shards.
Why this is correct
Cluster mode distributes data and load across multiple shards, increasing CPU and memory capacity.
Related concept
Read the scenario before looking for a memorised answer.
✗
Enable Multi-AZ replication for the Redis cluster.
Why it's wrong here
Multi-AZ provides high availability but does not increase capacity.
✗
Increase the instance size of the Redis cluster to a larger node type.
Why it's wrong here
Vertical scaling is limited and may not handle extreme spikes as well as horizontal scaling.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often confuse vertical scaling (increasing instance size) with horizontal scaling (adding shards), and fail to recognize that cluster mode is the only option that distributes both CPU and memory load across multiple nodes, which is necessary when a single node reaches 100% CPU utilization.
Detailed technical explanation
How to think about this question
Redis cluster mode uses a sharding architecture where each shard is a master-replica group, and the keyspace is partitioned into 16,384 hash slots. Clients use the Redis Cluster protocol (or a smart client like Lettuce) to route commands directly to the correct shard, avoiding a proxy bottleneck. In a real-world scenario, a gaming leaderboard application with millions of concurrent writes would benefit from cluster mode because it allows writes to be distributed across shards, preventing any single node from becoming a hot spot.
KKey Concepts to Remember
Read the scenario before looking for a memorised answer.
Find the constraint that changes the correct option.
Eliminate answers that are true in general but not in this case.
TExam Day Tips
→Watch for words such as best, first, most likely and least administrative effort.
→Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
An e-commerce site experiences heavy traffic on Black Friday and near-zero traffic during off-peak weeks. Rather than provisioning permanent large VMs, the team uses auto-scaling groups that add capacity automatically under load and reduce it overnight. Questions like this test whether you understand elasticity, availability zones, and cloud compute scaling patterns.
What to study next
Got this wrong? Here's your next step.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Continuous Improvement for Existing Solutions — This question tests Continuous Improvement for Existing Solutions — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Enable cluster mode for the Redis cluster and add more shards. — Enabling cluster mode for the Redis cluster and adding more shards horizontally partitions the data across multiple nodes, distributing both CPU and memory load. This directly addresses the 100% CPU and high memory utilization during traffic spikes, allowing the cluster to handle more concurrent requests without performance degradation. Cluster mode also provides linear scalability, which is essential for a critical web application experiencing variable traffic.
What should I do if I get this SAP-C02 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Question Discussion
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