Jumped straight to session stickiness and they seemed pleased, but I fumbled when they asked me to go further.
Start by restating the problem and identifying the most likely cause: session state not being shared across backend servers. Then walk through the architecture, explain how sticky sessions or a centralized session store would solve it, and discuss trade-offs. Finally, mention how you would diagnose and verify the issue.
Pro tip: Demonstrate that you consider both quick fixes (enabling sticky sessions) and robust long-term solutions (externalizing session state), and tie your answer to Amazon's Leadership Principles like Customer Obsession and Dive Deep.
Ask clarifying questions to understand the setup: Is the load balancer using round-robin? Are sessions stored in-memory on each server? What session management is in place?
Explain that without shared session state, each server has its own session data. When a user's request hits a different server, their session is not recognized, causing a logout.
Discuss two main approaches: sticky sessions (session affinity) at the load balancer, or externalizing session state to a shared store like Redis or a database.
Compare sticky sessions (simple but can cause uneven load and still fail if a server goes down) vs. centralized session store (more scalable and resilient but adds latency and complexity).
Mention how to confirm the issue: check load balancer logs for session stickiness, inspect server logs for session creation, and test with a shared session store to see if the problem persists.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.