The answer is to enable Cluster Mode and add multiple shards, because the single cache.r5.large node is overwhelmed by CPU saturation and MAXMEMORY evictions from increased concurrent users and session data. ElastiCache Redis Cluster Mode partitions data across shards, each handling a subset of keys, which reduces per-node CPU load and memory pressure—directly resolving the high CPU utilization and evictions caused by the session state growth. On the AWS Certified SAP on AWS Specialty PAS-C01 exam, this scenario tests your understanding that scaling vertically (larger node) is a secondary step; the primary fix for CPU-bound, memory-constrained workloads is horizontal scaling via sharding, especially when Cluster Mode is disabled. A common trap is to first scale up the node size, but that only delays the issue without addressing the CPU bottleneck from single-node processing. Memory tip: “Shard the load, not the node”—when CPU and memory both hit limits, distribute the data, don’t just enlarge the container.
PAS-C01 Operations and Maintenance Practice Question
This PAS-C01 practice question tests your understanding of operations and maintenance. 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.
A company runs a critical web application on a fleet of EC2 instances behind an Application Load Balancer (ALB) in an Auto Scaling group. The application stores session state in an ElastiCache Redis cluster (Cluster Mode disabled). The operations team receives alerts that the application is experiencing intermittent timeouts and high error rates. Upon investigation, they find that the Redis cluster's CPU utilization is consistently above 90%, and there are frequent 'MAXMEMORY' evictions. The application team confirms that they recently increased the number of concurrent users and added more session data per user. The current Redis cluster is a single cache.r5.large node with 13.37 GB of memory. Which of the following should the operations team do FIRST to address the performance issues?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "first"
Why it matters: Order matters here. You are being tested on which action comes before the others — not which action is generally useful.
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 and add multiple shards to distribute the data across nodes.
The correct first step is to enable Cluster Mode and add multiple shards because the performance issue stems from CPU saturation and memory pressure on a single Redis node. Cluster Mode distributes data across multiple shards, reducing per-node CPU load and memory usage, which directly addresses the high CPU utilization and 'MAXMEMORY' evictions caused by increased concurrent users and session data.
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.
✗
Upgrade the instance type to cache.r5.2xlarge to double the memory and compute capacity.
Why it's wrong here
Scaling vertically provides only a temporary solution and does not scale horizontally for future growth.
✗
Create a read replica in a different Availability Zone and redirect read traffic to it.
Why it's wrong here
Read replicas do not help with write-heavy workloads or reduce CPU load on the primary node.
✗
Change the eviction policy to 'allkeys-lru' to maximize memory utilization.
Why it's wrong here
Changing the eviction policy may evict important session data, causing application errors.
✓
Enable Cluster Mode and add multiple shards to distribute the data across nodes.
Why this is correct
Enabling Cluster Mode and adding shards allows horizontal scaling, distributing CPU and memory load.
Clue confirmation
The clue word "first" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often choose vertical scaling (Option A) or eviction policy changes (Option C) as quick fixes, failing to recognize that the scenario's high CPU and memory evictions indicate a need for horizontal scaling via sharding, which is the only option that directly reduces per-node load and memory pressure.
Detailed technical explanation
How to think about this question
In Redis Cluster Mode, data is automatically sharded across multiple nodes using a hash slot mechanism (16384 slots), which distributes CPU and memory load. The 'MAXMEMORY' eviction occurs when the node's memory limit is reached; with Cluster Mode, each shard has its own memory limit, reducing the chance of evictions on any single node. Additionally, Cluster Mode allows for replication per shard, improving fault tolerance, but the primary benefit here is horizontal scaling to handle increased session data and concurrent users.
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.
Operations and Maintenance — This question tests Operations and Maintenance — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Enable Cluster Mode and add multiple shards to distribute the data across nodes. — The correct first step is to enable Cluster Mode and add multiple shards because the performance issue stems from CPU saturation and memory pressure on a single Redis node. Cluster Mode distributes data across multiple shards, reducing per-node CPU load and memory usage, which directly addresses the high CPU utilization and 'MAXMEMORY' evictions caused by increased concurrent users and session data.
What should I do if I get this PAS-C01 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Are there clue words in this question I should notice?
Yes — watch for: "first". Order matters here. You are being tested on which action comes before the others — not which action is generally useful.
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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