Rolling upgrades

[squaremo]

https://botbot.me/freenode/weavenetwork/2015-02-18/?msg=32237468&page=1

Any thoughts on how I may perform a rolling update of weave without taking the whole cluster down?

[rade]

Bounce each node in turn. The new nodes won't be able to talk to the old ones IF the protocol revision has changed, so you end up with a sort of rolling partition which eventually disappears. We could do better, but not easily, so we'd need some evidence that what we have isn't enough.

[rade]

A few things we could do to improve the situation...

1. Maintain release branches and ship non-protocol-changing bug fix updates on them.
2. Switch to a major/minor scheme for the protocol version, with minor version changes being considered compatible.
3. Make the protocol resilient to "extra stuff", so that we can introduce some additions w/o bumping the major version.

However, some bug fixes / changes are simply too intrusive to maintain compatibility.

[rade]

We did (1) for the first time with the 0.11.1 release. We create release branches "just in time", i.e. when we need them, rather than at the time of the release.