Split Brain and Fencing¶

When network partitions create isolated groups, each group might believe it is the authoritative leader, causing conflicting decisions - fencing mechanisms ensure that old leaders cannot make progress once superseded.

Tension Addressed¶

Safety vs. Liveness

Recognizable As¶

Fencing tokens; epoch numbers; generation counters; lease expiration; STONITH (shoot the other node in the head); quorum-based leader election

Canonical Sources¶

Kleppmann, "Designing Data-Intensive Applications" (2017); Chockler, Keidar & Vitenberg, "Group Communication Specifications: A Comprehensive Study" (2001)

Transfers To¶

Distributed databases, cluster management, distributed locks, highly available systems

Split brain is particularly dangerous because both "leaders" may make valid decisions that conflict. Fencing ensures that even if an old leader is alive but isolated, it cannot cause damage. The monotonically increasing token/epoch is the key mechanism.