Chris Gioran describes rolling upgrades, a new feature in the upcoming Neo4j 1.8
So the rolling upgrade, actually, works exactly as you’d expect an upgrade would work. If there are not breaking changes between versions, you normally begin with the slaves, powering down, copying the store, migrating configuration if needed, then bringing that server back up. The new version would take over, communicate with the rest of the cluster and you wouldn’t notice anything.
A rolling upgrade offers that with versions that have incompatible protocols. Each slave, as it is brought up, detects the version running in the cluster and gracefully falls back into a compatibility mode that doesn’t allow it to become master, but allows it to continue to execute transactions.
Another thing I’ve found interesting is that the time a master machine is upgraded is considered the confirmation of a completed upgrade and all machines are switching to the new protocol. Clever.
Original title and link: Rolling Upgrades in Upcoming Neo4j 1.8 ( ©myNoSQL)