Distributed Systems Series — Part 4.8: Fault Tolerance & High Availability Distributed Systems Without Observability Are Black Boxes Every mechanism covered in Part 4 — failure detection, redundancy, self-healing, high availability architecture, fault isolation — produces value only if engineers can observe whether it is working. A Raft cluster that is experiencing unnecessary leader elections … Read more
Distributed Systems Series — Part 4.7: Fault Tolerance & High Availability Failures Are Inevitable — Outages Are Not Every large distributed system experiences component failures continuously. Nodes crash, networks degrade, downstream services slow, disks fill, processes run out of memory. The engineering discipline is not preventing these failures — that is impossible at scale — … Read more
Distributed Systems Series — Part 4.6: Fault Tolerance & High Availability High Availability Is a System-Level Property The availability nines defined in Post 4.2 — 99.9%, 99.99%, 99.999% — are measurements of an outcome. This post is about the architecture that produces that outcome. High availability cannot be achieved by adding redundancy to one layer … Read more
Distributed Systems Series — Part 4.5: Fault Tolerance & High Availability Detection Is Not Recovery Post 4.4 established how distributed systems detect failures — through heartbeats, timeouts, phi accrual detectors, and gossip protocols. Detection is the prerequisite. But detecting that a node has failed solves nothing by itself. The system must then do something about … Read more
Distributed Systems Series — Part 4.4: Fault Tolerance & High Availability The Question That Has No Perfect Answer When a distributed node stops responding, other nodes face a question that cannot be answered with certainty: has this node failed, or is it merely slow? In a single-machine system, this question does not exist. The operating … Read more
Distributed Systems Series — Part 4.3: Fault Tolerance & High Availability Redundancy Is the Foundation, Not the Solution Post 4.1 established the taxonomy of failures — crash-stop, crash-recovery, omission, timing, gray, Byzantine, and correlated. Post 4.2 established the distinction between fault tolerance (correctness under failure) and high availability (uptime). This post addresses the structural mechanism … Read more