What is leader election and how is it implemented in distributed systems?

Leader election selects one node as coordinator for a task, ensuring single active leader. Uses: distributed locks, primary database replica, job scheduling. Algorithms: Raft/Paxos (consensus-based), ZooKeeper (ephemeral nodes + watches), etcd (lease-based), Redis (SETNX with expiry). Requirements: detect leader failure, elect new leader quickly, prevent split-brain. Implementation: acquire lock/lease, maintain heartbeat, others monitor, re-election on failure. Fencing tokens prevent stale leaders from taking actions. Critical for consistency in distributed systems.