When to cache, which tool actually fits (Redis vs Memcached vs a key-value store), and the failure modes that come with either.
Can use it - fundamentals and hands-on basics.
Can troubleshoot it - real operational depth.
Can run it in production - reliability under pressure.
Can design and scale it - platform-engineering judgment.
Real scenario-based DevOps questions, hands-on practice, and clear explanations for every answer.