InterProcessSemaphoreV2.getParticipantNodes() would have ordinal numbers on each node - it's part of the recipe. But, use whichever method works best for you.
-Jordan On Jul 11, 2013, at 8:26 AM, Ignasi Rius <[email protected]> wrote: > 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 >>> >>
