Trying to join member with wrong ActorSystem name, but was ignored, expected [X] but was [Y]

[Eric Pederson]

Hi guys:

If one of my actor system names is different from the actor system name of the seed nodes I get this message:

WARN: Trying to join member with wrong ActorSystem name, but was ignored, expected [X] but was [Y]

And actually the cluster fails to start up at all.  If I change the actor system name to the same as the seed nodes then everything starts up fine.

Is having the same actor system name required?

This is using Akka 2.3.0. 

Thanks,

[Konrad Malawski]

Hello Eric,

Is having the same actor system name required?

Yes, for a cluster to converge the cluster members should have the same actorsystem-name.

I like to think of it as: the ActorSystem being the “universe” in which Actors live, the cluster just allows them to live on different “planets” (nodes) (in that abstract universe).
When you look at an actor path it also helps to reason about it - “more left == more general”. So in akka.tcp://Cluster...@127.0.0.1:2552/system/cluster/core/daemon,
the things that have to equal for a Cluster to be able to join another ActorSystem are both the protocol used as well as the actorsystem-name; The host, port, and rest of the path can (and will) differ between nodes.

Relevant lines are: https://github.com/akka/akka/blob/master/akka-cluster/src/main/scala/akka/cluster/ClusterDaemon.scala#L392-L397

I noticed we were not very explicit about this requirement in the docs… Will try to make it more explicit!
I hope this helps though!

PS: Do you have an use-case in mind where you might need to join differently named actor systems into the same cluster?

--

Cheers,

Konrad 'ktoso' Malawski

hAkker - Typesafe, Inc

[Eric Pederson]

Thanks Konrad - 

I have an app that launches cluster members by ssh-ing into each box and running a script.

The launcher app is joining the cluster to simplify the logic of knowing when everything is up.  I had a different actor system name for the launcher because it's a different app.  But it's not a big deal to have it use the same actor system name.

I'm probably going to move away from having the launcher join the cluster because there is a lot of log noise when the launcher app completes and leaves the cluster.  

Ideally you could subscribe to cluster events without actually joining the cluster, from a launching or monitoring perspective.

What I'll probably do is just send an Identify to an actor that should be living after the cluster member starts successfully.  

-- Eric

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[Carsten Saathoff]

Hi,

Am Montag, 7. April 2014 20:56:24 UTC+2 schrieb Eric Pederson:

I'm probably going to move away from having the launcher join the cluster because there is a lot of log noise when the launcher app completes and leaves the cluster.  

Ideally you could subscribe to cluster events without actually joining the cluster, from a launching or monitoring perspective.

have you seen the Cluster Client?

http://doc.akka.io/docs/akka/2.3.1/contrib/cluster-client.html

best

Carsten

[Eric Pederson]

Hi Carsten - yes.  It didn't seem to do what I needed but I may experiment with it later. 

Actually joining the cluster worked exactly how I wanted it except for the noise in the logs after the launcher app quits after the cluster is fully launched.  

I ended up using just plain remoting and Identify/ActorIdentity.

Thanks,

-- Eric

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