Modular Composition of Coordination Services


Coordination services like ZooKeeper, etcd, Doozer, and Consul are increasingly used by distributed applications for consistent, reliable, and high-speed coordination. When applications execute in multiple geographic regions, coordination service deployments trade-off between performance, (achieved by using independent services in separate regions), and consistency.

We present a system design for modular composition of services that addresses this trade-off. We implement ZooNet, a prototype of this concept over ZooKeeper. ZooNet allows users to compose multiple instances of the service in a consistent fashion, facilitating applications that execute in multiple regions. In ZooNet, clients that access only local data suffer no performance penalty compared to working with a standard single ZooKeeper. Clients that use remote and local ZooKeepers show up to 7x performance improvement compared to consistent solutions available today.