On Wed, Aug 30, 2017 at 11:24 AM, Igor Baltiyskiy <ios...@gmail.com> wrote:
> I'd like to clarify the warning given in the documentation: > > > We recommend against using the auto-down feature of Akka Cluster in > production. This is crucial for correct behavior if you use Cluster > Singleton <http://doc.akka.io/docs/akka/2.5/scala/cluster-singleton.html> > or Cluster Sharding > <http://doc.akka.io/docs/akka/2.5/scala/cluster-sharding.html>, > especially together with Akka Persistence > <http://doc.akka.io/docs/akka/2.5/scala/persistence.html>. For Akka > Persistence with Cluster Sharding it can result in corrupt data in case of > network partitions. > (http://doc.akka.io/docs/akka/2.5/scala/cluster-usage.html# > auto-downing-do-not-use-) > > This passage raises several questions: > > 1. Does it mean that auto-downing is *always* a bad idea? Or is it only a > bad idea when using Cluster Singleton and Cluster Sharding, so that if I'm > not using them, using auto-downing in production is perfectly fine? > It's a more or less *guaranteed* disaster in the long run with Cluster Sharding; it's only a *likely* disaster without, depending on what your app is doing. But personally, I think it should never, ever be used. Look at it this way: the problem with auto-down is that it is likely, in the long run, that you will eventually wind up in a Split Brain situation, with two or more disconnected clusters, each of which thinks that it is The One True Cluster and Source of Truth. This will usually happen in a realistic network, due to the vagaries of network traffic and the fundamental dumbness of the auto-down algorithm. Now, ask yourself: if this is acceptable -- if it is okay to sometimes *not* be a Cluster -- why are you using Clustering at all? Basically, if your nodes need to be able to share information in a consistent way, you need Clustering, which means that Split-Brain is deadly, which means that you must not use auto-down. If the nodes *don't* need to be sharing information, you probably shouldn't be bothering with Clustering at all, so auto-down is irrelevant. That's the heart of the argument, and why I personally think auto-down should be simply excised from the library entirely: it is *never* safe to use in anything more than a toy environment, and its existence just confuses people... -- >>>>>>>>>> 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 akka-user+unsubscr...@googlegroups.com. To post to this group, send email to akka-user@googlegroups.com. Visit this group at https://groups.google.com/group/akka-user. For more options, visit https://groups.google.com/d/optout.
