Yes, precisely what I was wondering, although probably not as well articulated!
I am curious as, to my limited knowledge, RAFT prohibits split-brain. Does that mean RAFT therefore sits at the 'unavailable' end of the continuum you described, or does it somehow provide slightly greater availability compared to more primitive schemes like a N>0.5•M quorum? Thanks, Lawrence On Friday, May 9, 2014 10:50:23 PM UTC+1, Eric Pederson wrote: > > Lawrence - were you wondering where the existing Akka-based Raft > implementations (eg. ktoso/akka-raft <https://github.com/ktoso/akka-raft>) > sit in Roland's auto downing to no downing spectrum and/or if RAFT has any > particular consistency requirements that map to one of Roland's categories? > I'm curious too. > > > -- Eric > > > On Fri, May 9, 2014 at 8:31 AM, Jonas Bonér <[email protected]<javascript:> > > wrote: > >> >> >> >> On Thu, May 8, 2014 at 5:35 PM, Lawrence Wagerfield < >> [email protected] <javascript:>> wrote: >> >>> Fascinating and very helpful! >>> >>> Out of interest, where does RAFT sit on the aforementioned spectrum? I >>> only ask as there's a few Akka RAFT implementations floating around... >>> >> >> We have not talked about adding Raft (or similar, like Paxos/VR) to the >> Akka distribution. As everything in Akka, features are driven by need. If >> it turns out to be an important building block, either as an >> abstraction/tool for our users, or internally (if we f.e. decide to >> implement our own replicated Akka Persistence Journal) then we will add it. >> Many of the good things in Akka started out as external contributions, that >> after proven essential, was added to the core distribution—examples are >> Spray, eventsourced and Akka Camel. >> >> >>> >>> On Monday, May 5, 2014 7:07:16 AM UTC+1, shikhar wrote: >>>> >>>> I have been hacking on a discovery plugin for >>>> elasticsearch<https://github.com/shikhar/eskka> using >>>> akka cluster and I wanted to add some automated downing, and the >>>> auto-down-unreachable-after is not really an option since it can lead to >>>> split brain. >>>> >>>> So I went with the approach of using a quorum of members to determine >>>> whether the unreachable node should be downed. I'm curious to hear what >>>> you >>>> think of this. >>>> >>>> see https://github.com/shikhar/eskka/blob/master/src/main/scala/eskka/ >>>> QuorumBasedPartitionMonitor.scala >>>> >>>> 1. The >>>> VotingMembers<https://github.com/shikhar/eskka/blob/release-0.1/src/main/scala/eskka/VotingMembers.scala>passed >>>> in the constructor are the seed nodes. Using seed nodes was just an >>>> easy choice since they are specified before-hand. So ideally there should >>>> be 3 or more seed nodes. >>>> >>>> 2. I am using an app-level ping >>>> layer<https://github.com/shikhar/eskka/blob/master/src/main/scala/eskka/Pinger.scala>on >>>> top of the UNREACHABLE events. When a ping request to an unreachable >>>> node, made via the seed nodes "affirmatively times-out" (i.e. they must >>>> explicitly return a timeout response rather than the ping request timing >>>> out, so that we don't consider an unreachable seed-node as a voter!), then >>>> we DOWN that unreachable node. Instead of these app-level pings maybe it >>>> makes sense to utilize the Akka private[cluster] metadata >>>> like Reachability.isReachable(observer, node) but I'm not entirely >>>> sure of the semantics. >>>> >>>> 3. Currently this QuorumBasedPartitionMonitor actor gets started on >>>> every seed node. So in case a member becomes unreachable, they'd all end >>>> up >>>> trying to arrange for a distributed ping to the unreachable node via one >>>> another, and possibly downing it. This seems a bit like a thundering herd >>>> so not ideal. But on the other hand I don't want to use a >>>> cluster-singleton >>>> because this partition resolver is trying to be the layer that allows for >>>> singleton failover to happen smoothly. I'd love to hear ideas on how to >>>> handle this better. >>>> >>>> 4. Maybe a generic solution for quorum-based partition resolution >>>> should be a part of Akka proper/contrib? It seems AutoDown is rarely a >>>> good >>>> answer. >>>> >>> -- >>> >>>>>>>>>> Read the docs: http://akka.io/docs/ >>> >>>>>>>>>> Check the FAQ: >>> http://doc.akka.io/docs/akka/current/additional/faq.html >>> >>>>>>>>>> Search the archives: >>> https://groups.google.com/group/akka-user >>> --- >>> You received this message because you are subscribed to the Google >>> Groups "Akka User List" group. >>> To unsubscribe from this group and stop receiving emails from it, send >>> an email to [email protected] <javascript:>. >>> To post to this group, send email to [email protected]<javascript:> >>> . >>> Visit this group at http://groups.google.com/group/akka-user. >>> For more options, visit https://groups.google.com/d/optout. >>> >> >> >> >> -- >> >> *Jonas Bonér*Phone: +46 733 777 123 >> Home: jonasboner.com >> Twitter: @jboner <https://twitter.com/jboner> >> >> -- >> >>>>>>>>>> Read the docs: http://akka.io/docs/ >> >>>>>>>>>> Check the FAQ: >> http://doc.akka.io/docs/akka/current/additional/faq.html >> >>>>>>>>>> Search the archives: https://groups.google.com/group/akka-user >> --- >> You received this message because you are subscribed to a topic in the >> Google Groups "Akka User List" group. >> To unsubscribe from this topic, visit >> https://groups.google.com/d/topic/akka-user/UBSF3QQnGaM/unsubscribe. >> To unsubscribe from this group and all its topics, send an email to >> [email protected] <javascript:>. >> To post to this group, send email to [email protected]<javascript:> >> . >> Visit this group at http://groups.google.com/group/akka-user. >> For more options, visit https://groups.google.com/d/optout. >> > > -- >>>>>>>>>> Read the docs: http://akka.io/docs/ >>>>>>>>>> Check the FAQ: >>>>>>>>>> http://doc.akka.io/docs/akka/current/additional/faq.html >>>>>>>>>> Search the archives: https://groups.google.com/group/akka-user --- You received this message because you are subscribed to the Google Groups "Akka User List" group. 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