Akka cluster management using etcd
Running an Akka cluster requires establishing a set of seed nodes. The purpose of them is two-fold: all nodes joinig the cluster do so by contacting any of the seed nodes over the network, and one of the seed nodes bootstraps the cluster by "joining itself" - establishing a new cluster with size 1.
This creates an administrative burden: care must be taken to start that only one of the seed nodes will perform cluster bootstrap (otherwise a the cluster will become partitioned from the very outset) and secondly the IP address list of seed nodes needs to be kept up to date and used whenever a new instance of the application is started.
There are several cloud application platforms based on Docker (Kubernetes, Fleet) etcd is used as a distributed configuration store that is used by the platform for workload scheduling and maintaining SDN (Weave, Flannel) but it is also available for applications to use. An instance of etcd can be assumed to run on each of the cluster's nodes (Docker hosts) and to be reachable on a fixed IP address visible in the application Docker container. etcd can be then used to discover existing Akka cluster nodes, and also elect the initial seed node, thanks to consistency guarantees provided by etcd. This enables a zero-configuration deployment scenario for Akka cluster.