Hi Jordan, Eric, thanks for your advices. InterProcessSemaphoreV2.getParticipantNodes() is fine, but as Jordan says, I would like that each participant knows who it is ordinally. The reason is that I would like to use this number as an identifier for the "role" I want that node to fulfill.
Eric's suggestion will do the job and looks pretty easy to implement and mantain. I will store a "list of roles" somewhere, and once a node acquires de semaphore, it will try to create each "role node" until it succeeds. That's it. Thanks! 2013/7/10 Eric Tschetter <[email protected]>: > The other option is to have a specific znode for each "role" that you want > fulfilled. On startup, you have each process race to claim one of those > znodes by creating an ephemeral node. If it manages to create its ephemeral > node, then it acts as that role. If it gets a NodeExistsException, then it > tries another role. > > This is similar to electing a leader for each role. It does cause some > stampeding when a node goes down, though. There also is no recipe for this > currently. > > --Eric > > > On Wednesday, July 10, 2013, Jordan Zimmerman wrote: >> >> I would use InterProcessSemaphoreV2. Does each node need to know which >> participant it is ordinally? If so, I'm curious why. In any event, you can >> use setNodeData() to set an identifier for each participant. Just like >> LeaderLatch InterProcessSemaphoreV2 has a getParticipantNodes() method. >> >> -Jordan >> >> On Jul 10, 2013, at 3:18 AM, Ignasi Rius <[email protected]> wrote: >> >> > Hi all, >> > >> > I am a newbie to Zookeeper and Curator. After a couple of weeks >> > reading, testing and playing with it, I am quite convinced that it is >> > a great solution for our cluster management needs. >> > >> > I would like to ask you some advice on how could I implement the >> > following behaviour based on Curator recipes: >> > >> > We provide a service which is split/distributed among N nodes, and we >> > would like to implement a N+1 redundancy strategy. That is N active >> > nodes plus 1 spare node which can "behave" as any of the others. >> > >> > Indeed, when each node starts, it should take the following role: >> > - a) Behave like a Spare Node: iif there are already "N" nodes working. >> > - b) Behave like node (M+1): if (M < N) (assuming M is the number of >> > current workers). >> > >> > Then, in case that any of the N working nodes dies, the Spare one >> > should behave like the one that died. >> > >> > >> > Summarizing, as an exemple with 3 hosts (1,2 and 3) this is a >> > possible sequence of events: >> > >> > - Host 1 starts and acts as Node 1. >> > - Host 2 starts and acts as Node 2. >> > - Host 3 starts and acts as a Spare Node. >> > - Host 2 dies. >> > - Host 3 takes over and acts as Node 2. >> > >> > >> > My question is about what do you guys think would be the best >> > "practice" for implementing such scenario? >> > >> > I thought that the simplest thing to do was using an >> > InterProcessSemaphoreV2 (N), so if a node can acquire the semaphore, >> > it means that it is not the "Spare" one. However, I don't see a way in >> > Curator to find out "which node I am" in case I can acquire de >> > semaphore. >> > >> > On the contrary, LeaderLatch seems to handle participant IDs, etc... >> > but there is only "one leader" at a time (obviusly). >> > >> > Thanks for your time. Any ideas are welcome. >> > >> > Best, >> > Ignasi >> >
