DVA-C02 Question #380: Real Exam Question with Answer & Explanation

Question

A developer is designing a fault-tolerant environment where client sessions will be saved. How can the developer ensure that no sessions are lost if an Amazon EC2 instance fails?

Options

• AUse sticky sessions with an Elastic Load Balancer target group.
• BUse Amazon SQS to save session data.
• CUse Amazon DynamoDB to perform scalable session handling.
• DUse Elastic Load Balancer connection draining to stop sending requests to failing instances.

Explanation

To survive EC2 instance failures, session state must be stored in an external, fault-tolerant data store rather than in instance memory. DynamoDB provides a managed, highly available key-value store ideal for session data.

Common mistakes.

• A. Sticky sessions route a client to the same EC2 instance, so if that instance fails, the session stored in memory is lost along with it.
• B. Amazon SQS is a message queuing service designed for decoupling components, not for storing and retrieving key-value session data.
• D. Connection draining gracefully stops new requests to a failing instance but does not persist or recover session data stored in instance memory.

Concept tested. External session state management with DynamoDB

Reference. https://docs.aws.amazon.com/amazondynamodb/latest/developerguide/bp-session-handling.html

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