- A
Amazon ElastiCache for Memcached with session data stored as key-value pairs
Why wrong: Memcached supports only simple key-value pairs and cannot perform sorted set operations. Memcached also lacks replication — a node failure destroys all cached sessions.
- B
Amazon DynamoDB with TTL enabled for session expiration
Why wrong: DynamoDB achieves single-digit millisecond latency, not sub-millisecond. It also lacks native sorted set operations. ElastiCache Redis provides the required sub-millisecond in-memory latency.
- C
Amazon ElastiCache for Redis with sessions stored as sorted sets
Redis provides sub-millisecond latency, sorted sets for ordering by last-access score, Multi-AZ replication, and external storage for cross-instance availability. All requirements are met.
- D
ElastiCache for Redis with sticky sessions enabled on the Application Load Balancer
Why wrong: ALB sticky sessions pin clients to specific EC2 instances. If an instance fails, those sessions are lost. External Redis sessions (without ALB stickiness) are the correct cross-instance resilient approach.
Quick Answer
The answer is Amazon ElastiCache for Redis with sessions stored as sorted sets. This solution meets every requirement because Redis natively supports the sorted set (ZSET) data structure, which allows you to assign a score—such as a Unix timestamp of the last access time—to each session ID, enabling the cache to efficiently order and expire the oldest sessions first. On the SAA-C03 exam, this scenario tests your ability to distinguish between Redis and Memcached under the specific constraint of needing sorted operations for session management; a common trap is choosing Memcached for its simplicity, but it only handles simple key-value pairs and lacks the sorted set capability as well as replication, meaning a node failure would lose all sessions. Remember the memory tip: “Redis sorts, Memcached stores”—if you need to rank or order data by a score, Redis is the only choice.
SAA-C03 Practice Question: ElastiCache Redis supports sorted sets (ZSET) for…
This SAA-C03 practice question tests your understanding of design high-performing architectures. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. A key principle to apply: elastiCache Redis supports sorted sets (ZSET) for ordering data by score — ideal for session expiry queues. 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 needs to implement session management for a web application. Sessions must persist across multiple EC2 instances, survive EC2 failures, and be accessible with sub-millisecond latency. Sessions must also be sortable by last-access time to expire the oldest sessions first. Which caching solution should a solutions architect recommend?
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 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
Amazon ElastiCache for Redis with sessions stored as sorted sets
Amazon ElastiCache for Redis satisfies all requirements: multi-instance session sharing (sessions stored externally), sub-millisecond latency, survival of EC2 failures (stored outside instances), and sorted sets (ZSET data structure) for ordering sessions by last-access score. Memcached supports only simple key-value pairs — it cannot perform sorted set operations to order sessions by last-access time. Memcached also lacks replication, meaning a node failure loses all cached sessions.
Key principle: ElastiCache Redis supports sorted sets (ZSET) for ordering data by score — ideal for session expiry queues
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Amazon ElastiCache for Memcached with session data stored as key-value pairs
Why it's wrong here
Memcached supports only simple key-value pairs and cannot perform sorted set operations. Memcached also lacks replication — a node failure destroys all cached sessions.
- ✗
Amazon DynamoDB with TTL enabled for session expiration
Why it's wrong here
DynamoDB achieves single-digit millisecond latency, not sub-millisecond. It also lacks native sorted set operations. ElastiCache Redis provides the required sub-millisecond in-memory latency.
- ✓
Amazon ElastiCache for Redis with sessions stored as sorted sets
Why this is correct
Redis provides sub-millisecond latency, sorted sets for ordering by last-access score, Multi-AZ replication, and external storage for cross-instance availability. All requirements are met.
Clue confirmation
The clue word "first" in the question point toward this answer.
Related concept
ElastiCache Redis supports sorted sets (ZSET) for ordering data by score — ideal for session expiry queues
- ✗
ElastiCache for Redis with sticky sessions enabled on the Application Load Balancer
Why it's wrong here
ALB sticky sessions pin clients to specific EC2 instances. If an instance fails, those sessions are lost. External Redis sessions (without ALB stickiness) are the correct cross-instance resilient approach.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Memcached and Redis are both ElastiCache engines, but they serve different needs. Any requirement involving sorted data, complex data structures, persistence, or replication eliminates Memcached. Redis sorted sets (ZSET) store members with numeric scores and support range queries — perfect for session expiry queues ordered by last-access timestamp.
Detailed technical explanation
How to think about this question
ElastiCache Redis vs Memcached: | Feature | Redis | Memcached | | Data types | Strings, lists, sets, sorted sets, hashes | Strings only | | Persistence | Yes (RDB, AOF) | No | | Replication/Multi-AZ | Yes | No | | Pub/Sub | Yes | No | | Multi-threading | No (single core) | Yes | Redis sorted set commands for sessions: ZADD sessions <timestamp> <session_id> ZRANGEBYSCORE sessions 0 <cutoff_time> -- get expired sessions ZREM sessions <session_id> -- remove session Sub-millisecond note: ElastiCache delivers microsecond-range latency for in-memory operations. DynamoDB achieves single-digit millisecond — faster than disk but slower than in-memory cache.
KKey Concepts to Remember
- ElastiCache Redis supports sorted sets (ZSET) for ordering data by score — ideal for session expiry queues
- Redis supports persistence (RDB snapshots, AOF) and Multi-AZ replication
- Memcached supports only simple key-value pairs with no data structure operations
- ElastiCache delivers sub-millisecond (microsecond) in-memory latency
- Externalizing sessions to ElastiCache makes them available across all EC2 instances
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
ElastiCache Redis supports sorted sets (ZSET) for ordering data by score — ideal for session expiry queues
Real-world example
How this comes up in practice
A company's IT admin needs to give a contractor read-only access to production logs without sharing account credentials. Using role-based access control (RBAC) and temporary scoped permissions — not a permanent shared password — is the correct pattern. Questions like this test whether you can apply least-privilege access across cloud identity services.
What to study next
Got this wrong? Here's your next step.
Review elastiCache Redis supports sorted sets (ZSET) for ordering data by score — ideal for session expiry queues, then practise related SAA-C03 questions on the same topic to reinforce the concept.
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FAQ
Questions learners often ask
What does this SAA-C03 question test?
Design High-Performing Architectures — This question tests Design High-Performing Architectures — ElastiCache Redis supports sorted sets (ZSET) for ordering data by score — ideal for session expiry queues.
What is the correct answer to this question?
The correct answer is: Amazon ElastiCache for Redis with sessions stored as sorted sets — Amazon ElastiCache for Redis satisfies all requirements: multi-instance session sharing (sessions stored externally), sub-millisecond latency, survival of EC2 failures (stored outside instances), and sorted sets (ZSET data structure) for ordering sessions by last-access score. Memcached supports only simple key-value pairs — it cannot perform sorted set operations to order sessions by last-access time. Memcached also lacks replication, meaning a node failure loses all cached sessions.
What should I do if I get this SAA-C03 question wrong?
Review elastiCache Redis supports sorted sets (ZSET) for ordering data by score — ideal for session expiry queues, then practise related SAA-C03 questions on the same topic to reinforce the concept.
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?
ElastiCache Redis supports sorted sets (ZSET) for ordering data by score — ideal for session expiry queues
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Last reviewed: May 17, 2026
This SAA-C03 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 SAA-C03 exam.
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