I don't think that this is an issue now since you can use roles and "spread out" the cluster-singletons that way.
That the cluster-singleton can be made to only start on a node with a specific role is perfectly clear from the documentation. What I think that what could be improved is this part: > The singleton actor is always running on the oldest member, which can be > determined by Member#isOlderThan. This can change when removing that > member from the cluster. Be aware that there is a short time period when > there is no active singleton during the hand-over process. > It probably should say something like: The singleton actor is always running on the on the oldest member with specified role ... To avoid getting stupid questions from people like me :) Thanks for helping me out! On Friday, April 3, 2015 at 6:04:36 PM UTC+2, Patrik Nordwall wrote: > > > > > 3 apr 2015 kl. 17:34 skrev Akka Team <[email protected] <javascript:>>: > > Hello Olle, > > Are there any way of not having all cluster-singleton actors running on >> the same node ( the leader node of the cluster ) in case that a service >> needs to be migrated to another node because of other reasons than a node >> is down ( out of disk space or something like that ). > > It does not have to be running on the cluster leader - it can run on > "oldest node that has a given role", it's documented here: > http://doc.akka.io/docs/akka/current/contrib/cluster-singleton.html > > So you can have roles like "backend" or "cpu-heavy" and then the singleton > would be running on the oldest cluster member that contains each its > required role. > We do not support very dynamic moving of singletons around as you seem to > be asking for. > Singletons are usually used for light "master" or "scheduler" Actors, and > the actual work would be performed by some sharded workers. > > Do you feel you have a strong use-case for it or are just wondering if > it's possible? > > > I noticed that you can use roles for the cluster-singleton, what happens >> if a new leader is elected but without the roles needed for a particular >> cluster singleton would that service be spun up on a non-leader node ? > > The cluster "leader" is not what decides where the singleton is being run. > The singleton is running on "oldest node, that matches it's role > requirements". > > Yes, if you do not require any roles, this requirement matches with the > node that we call the cluster leader, but as you see the singleton may (and > often will) run on non-leader nodes. > > > Let me clarify the terminology. What we call cluster leader is actually > the node with the lowest address (sorted by hostname:port). That is not the > same as the oldest node. Singleton runs on the oldest node (with matching > role requirements). > > This is not the first time this comes up. Is the documentation wrong > somewhere? > > /Patrik > > > Hope this helps! > > > -- Konrad > > On Tue, Mar 31, 2015 at 8:38 AM, <[email protected] <javascript:>> > wrote: > >> Hi, >> >> A couple of questions regarding the cluster-singleton functionality: >> >> - Are there any way of not having all cluster-singleton actors >> running on the same node ( the leader node of the cluster ) in case that >> a >> service needs to be migrated to another node because of other reasons >> than >> a node is down ( out of disk space or something like that ). >> - I noticed that you can use roles for the cluster-singleton, what >> happens if a new leader is elected but without the roles needed for a >> particular cluster singleton would that service be spun up on a >> non-leader >> node ? >> >> Thanks, Olle >> >> >> >> -- >> >>>>>>>>>> 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. >> > > > > -- > Akka Team > Typesafe - Reactive apps on the JVM > Blog: letitcrash.com > Twitter: @akkateam > > -- > >>>>>>>>>> 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. > > -- >>>>>>>>>> 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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