Nettle: Functional Reactive Programming of OpenFlow Networks

We describe a language-centric approach to solving the complex, low-level, and error-prone problem of network control. Specifically, we have designed a domain-specific language called Nettle, embedded in Haskell, that allows programming OpenFlow networks in an elegant, declarative style. Nettle is based on the principles of functional reactive programming (FRP), and as such has both continuous and discrete abstractions, each of which is leveraged in the design of Nettle: using the discrete nature of FRP we are able to elegantly capture control messages to and from OpenFlow switches as streams of Nettle events; using the continuous nature of FRP we are able to express dynamic load balancing algorithms in a concise manner, reflecting directly the mathematics of the underlying control system. We have implemented Nettle and tested it on real OpenFlow switches. We demonstrate our methodology by writing several non-trivial OpenFlow controllers.