How would you implement a distributed locking mechanism?

Requirements: mutual exclusion, deadlock avoidance, fault tolerance. Redis approach: SET key value NX EX (set if not exists with expiry), owner token for safe release. Redlock (multi-node): acquire lock on majority of independent nodes. ZooKeeper: ephemeral sequential nodes, watch for predecessor deletion. Challenges: lock holder failure (TTL), clock drift (fencing tokens), split-brain. Best practices: always set timeout, use fencing tokens to detect stale locks, prefer local coordination when possible. Libraries: Redisson, Curator. Consider: is strong consistency needed, or eventual consistency acceptable?