I’ve been unsuccessful in trying to get an akka-cluster application that works
fine with one instance to work when there are multiple members of the clusters.
A bit of background is in order:
1) the application is an akka-cluster-sharing application
2) it runs in a docker container
3) the cluster is comprised of multiple docker hosts, each running the akka
application
4) the error I’m getting is this:
[WARN] [03/19/2016 01:39:18.086]
[ClusterSystem-akka.actor.default-dispatcher-3]
[akka.tcp://ClusterSystem@10.0.3.170:2552/system/sharding/ExperimentInstance]
Trying to register to coordinator at
[Some(ActorSelection[Anchor(akka://ClusterSystem/),
Path(/system/sharding/ExperimentInstanceCoordinator/singleton/coordinator)])],
but no acknowledgement. Total [1] buffered messages.
[WARN] [03/19/2016 01:39:20.086]
[ClusterSystem-akka.actor.default-dispatcher-3]
[akka.tcp://ClusterSystem@10.0.3.170:2552/system/sharding/ExperimentInstance]
Trying to register to coordinator at
[Some(ActorSelection[Anchor(akka://ClusterSystem/),
Path(/system/sharding/ExperimentInstanceCoordinator/singleton/coordinator)])],
but no acknowledgement. Total [1] buffered messages.
5) the warning message is logged repeatedly and the cluster never initializes.
6) I’ve set the following config parameters:
akka.remote.netty.tcp.hostname: to the actual host ip address (the one
accessible from all the other docker hosts)
akka.remote.netty.tcp.bind-hostname: to 0.0.0.0 (so that it binds on
the docker0 interface, on the ip address of the container)
akka.remote.netty.tcp.port: 2552
akka.remote.netty.tcp.bind-port:2552
7) when I start the container, I map port 2552 on the host to port 2552 on the
container.
8) from the host, I’m able to do a “telnet <ip-address-of-host> 2552” so I
should be taking to the akka-remoting handler.
9) I’m setting the akka..cluster.seed-nodes to a list of one element:
akka.tcp://ClusterSystem@<ip-address-of-host>:2552. I’m doing that because, as
far as I know, this seed-node list is advertised to all the other members of
the cluster (currently just the one) and must be accessible to them all. The
Docker container ip address (seen by the docker container) is on the private
docker0 interface, which is not accessible from the outside (from outside the
host).
Now, before I tried all this, I set seed-nodes to a list of a single
aka.tcp://ClusterSystem@127.0.0.1:2552 entry, and left
akka.remote.netty.tcp.hostname, bind-hostname, port, and bind-port to their
default values. In this configuration, the cluster comes up perfectly fine and
the application (with an akka-http frontend and a cluster sharing backend)
works perfectly. In fact, when I use two seed nodes of the same form, but
different ports on the same local 127.0.0.1 host, and two instances of the app
(each binding to the different ports), the app works fine too. The cluster
comes up find and each node finds the other.
But in a real environment, the multiple instances will be on different nodes
(diffferent ip addresses), and in my case, as docker containers on different
docker hosts. So clearly, the seed nodes must have externally accessible ip
addresses.
Can anyone shed any light on what might be going wrong?
How might I debug this? Thank. — Eric
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