Split-brain.
Two captains both think they’re in charge after the radio cuts out.
- 1
A healthy cluster: one leader, the rest follow its lead.
- Hello? Anyone?2
The network splits — the two halves can no longer reach each other.
- I’m in charge now.3
Each half assumes the leader is gone and elects its own. Two captains.
- 4
Both accept writes, so the two sides drift into conflicting data.
- 5
When the link heals, whose version is right? Now there’s a conflict to untangle.
- 6
The fix: require a majority (quorum) to lead, so only one side ever can.
Semicolony semicolony.dev/eli5/split-brain/comic