To be honest my favorite part of SmartStack is that you are not tied to a single discovery backend or mechanism. Both Synapse and Nerve support custom backends using whatever system you want (zookeeper, etcd, DNS, etc). At the end of the day both just expose basic configuration files and we exploit that at Yelp to do pretty cool stuff like allowing multiple systems to inform nerve/synapse about services (e.g. marathon or puppet) and allowing us to control service latency using a DSL that compiles down to those configuration files.
Just to clear something up, we have not found it necessary to run zookeeper at a cross datacenter level to get multidatacenter support. We're still working on writing up the details but the general gist is run zk in all datacenters and then cross register from a single nerve instance to multiple datacenters. That's why we had to remove fast fail from nerve, because by its nature cross datacenter communication is flakey. This approach has some tradeoffs however, as all approaches do.
All that being said, this is an interesting system and I look forward to more mindshare in the area of service discovery!
Just to clear something up, we have not found it necessary to run zookeeper at a cross datacenter level to get multidatacenter support. We're still working on writing up the details but the general gist is run zk in all datacenters and then cross register from a single nerve instance to multiple datacenters. That's why we had to remove fast fail from nerve, because by its nature cross datacenter communication is flakey. This approach has some tradeoffs however, as all approaches do.
All that being said, this is an interesting system and I look forward to more mindshare in the area of service discovery!