http://the-paper-trail.org/blog/?p=173

and http://the-paper-trail.org/blog/?p=190

for some tutorials I wrote on the subject.

You're correct that failure detection and consensus are very deeply related, in that a strong failure detector is 'sufficient' for consensus.

But my point is about client failure detection, not failure detection between servers (which must have some kind of timeout system; that's ok - you just sacrifice liveness in a few pathological cases rather than sacrificing correctness). If I am to implement leader election with Doozer, does Doozer provide any tools to help us with deciding when to elect a new leader? There's no reason it should, but ZooKeeper, for example, does have that in its arsenal.

Doozer doesn't, AFAIK, expose consensus as a primitive; that's not its model. So the fact that it uses Paxos, or ZAB, or 2PC or whatever doesn't make a difference to its clients.