Why a Healthy Cluster Refuses Your Writes: A Working Model of Raft
You don't implement consensus, but you operate it every day — etcd, Consul, CockroachDB, Kafka's KRaft. This is the mechanism behind the elections, the read-only clusters, and the fsync obsession: enough Raft to turn its surprises into diagnoses.
The cluster is up. Every node reports healthy. It's refusing writes.
Writes froze for nine seconds, then recovered on their own. Nothing in the logs looks broken.
Both read like bugs. Neither is. In both cases the system is doing exactly what its algorithm promises — and the only reason they feel like mysteries is that the algorithm is the one piece most of us never got around to learning.
That's a fair thing to have skipped. Almost nobody implements consensus from scratch; the papers are dense, and the systems built on it are reliable enough that you can run them for years without opening the hood. But implement and operateare...
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