DOP-C02 Resilient Cloud Solutions Practice Question
A company runs a containerized application on Amazon ECS with Fargate. The application needs to store session state. Which service provides the MOST resilient and scalable solution?
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
Amazon ElastiCache for Redis provides a highly available, scalable, and low-latency in-memory data store ideal for session state management in a containerized environment. It supports replication and automatic failover, ensuring resilience. Option B (Amazon EFS) is a file storage service with higher latency and not designed for sub-millisecond session retrieval. Option C (ephemeral storage on the container instance) is not durable; data is lost when the container stops or fails. Option D (Amazon S3) is object storage with higher latency and not optimized for frequent read/write operations required for session state.
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 Redis
Why this is correct
Amazon ElastiCache for Redis is a fully managed in-memory data store that provides sub-millisecond read/write latencies and is ideal for storing transient session state. It supports replication across Availability Zones and automatic failover, so the session store remains available even if a container task is rescheduled or an Availability Zone fails. Because it is external to the ECS task, the session data persists independently of the container lifecycle, enabling stateless containers and horizontal scaling of the web tier.
- ✗
Amazon EFS
Why it's wrong here
Amazon EFS provides a shared POSIX-compliant network file system that can be mounted into ECS containers to share files, but it is a poor fit for session state. Each session lookup incurs network file protocol overhead and higher latency than an in-memory key-value store, and the file-based access pattern does not efficiently handle high-frequency per-request operations like session get/set. Additionally, EFS requires lifecycle management and throughput provisioning considerations that add complexity compared to a purpose-built cache.
- ✗
Ephemeral storage on the container instance
Why it's wrong here
Ephemeral storage on the container instance consists of local instance store volumes that are tied to the EC2 host and the container's runtime. This storage is not durable; it is lost when the ECS task stops, is restarted, or when the container instance is replaced, and it cannot be shared across multiple tasks or instances. Relying on it for session state would cause users to be logged out or lose session data during any rolling deployment, task rescheduling, or instance scaling event.
- ✗
Amazon S3
Why it's wrong here
Amazon S3 is a durable, scalable object storage service, but it is optimized for throughput and large objects, not for low-latency, high-rate updates of small session records. Each read/write operation involves HTTPS request overhead and latency that is orders of magnitude higher than an in-memory cache, and performance would degrade under the volume of per-request session lookups. Using S3 also introduces cost and lifecycle complexity for data that is inherently transient and should not require deletion policies.
Quick reference
AWS S3 Storage Class Comparison
| Storage Class | Min Duration | Retrieval | Use Case |
|---|---|---|---|
| S3 Standard | None | Immediate | Frequently accessed data |
| S3 Standard-IA | 30 days | Immediate | Infrequent access, rapid retrieval |
| S3 One Zone-IA | 30 days | Immediate | Non-critical infrequent data |
| S3 Intelligent-Tiering | None | Immediate–hours | Unknown or changing access patterns |
| S3 Glacier Instant | 90 days | Milliseconds | Archive with instant retrieval |
| S3 Glacier Flexible | 90 days | Minutes–hours | Archive, flexible retrieval |
| S3 Glacier Deep Archive | 180 days | Hours | Long-term compliance archive |
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This DOP-C02 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 DOP-C02 exam.