Heartbeats
A heartbeat is a periodic 'I'm still alive' signal, and its timeout is the one knob that trades false-positive failovers against slow failure detection.
Service Discovery
Service discovery lets services find each other's current address dynamically instead of by hardcoded config, kept accurate by heartbeats to a registry.
Consensus Algorithms
Consensus is how multiple nodes agree on one value safely, even with failures — it's what makes split-brain mathematically impossible, not just unlikely.
Distributed Locking
A distributed lock makes sure only one actor holds a resource at a time across machines. Covers leases, and the fencing token that closes a subtle race.
Gossip Protocol
A gossip protocol spreads cluster state peer-to-peer, like a rumor, avoiding the O(n²) cost of every node pinging every other node directly.
Circuit Breaker
A circuit breaker stops calling a failing dependency after enough errors, failing fast instead of piling up timeouts. Covers its three-state recovery cycle.
Disaster Recovery
Disaster recovery plans for an entire region going dark, not just one node. Covers RPO, RTO, and the cost ladder from cold backups to active-active.
Distributed Tracing
Distributed tracing follows one request across every microservice it touches, using trace IDs and spans to answer 'which hop was actually slow.'