[zoips]

You're conflating their target functions. etcd is all about configuration distribution. Serf seems more like its about member discovery. So you might have a service you run in multiple clusters. Each cluster has a different configuration (etcd), and each instance in a cluster needs to know about the others in the same cluster because they talk to each other (Serf). You could make etcd handle all this, but it probably wouldn't do it as well (Serf has heart beats and recognizes dead nodes, etcd won't do that except for etcd nodes themselves).