Etcd has been phenomenal. In terms of solving the simple KV HA story, I can't think of a single technology that I have ever used that is as simple to set up and operate. We run etcd clusters with millions of keys and 500+/sec write rates and I can count on one hand the number of problems / tunings / issues we've had over the last two years.
There are lots of reasons why you might not want to use etcd, but if you can live with simple K/V, need HA, and need something that is simple and just works, I can't think of anything else that is comparable except for Consul (which I haven't used much, but has similar design principles).
There are lots of reasons why you might not want to use etcd, but if you can live with simple K/V, need HA, and need something that is simple and just works, I can't think of anything else that is comparable except for Consul (which I haven't used much, but has similar design principles).