MiCA: A Compositional Architecture for Gossip Protocols

C o n si st en t * lete * W ll D o c u m e n t e d * E a s y t o R e u s e * * E v a l u a t e d * E C O O P * Ar tifact * A E C The developers of today’s cloud computing systems are expected to not only create applications that will work well at scale, but also to create management services that will monitor run-time conditions and intervene to address problems as conditions evolve. Management tasks are generally not performance intensive, but robustness is critical: when a large system becomes unstable, the management infrastructure must remain reliable, predictable, and fault-tolerant. A wide range of management tasks can be expressed as gossip protocols where nodes in the system periodically interact with random peers and exchange information about their respective states. Although individual gossip protocols are typically very simple, by composing multiple protocols one can create a wide variety of interesting, complex functionality with strong (albeit probabilistic) robustness and convergence guarantees. For example, in a system with a sufficiently dense topology, all nodes will learn the information being disseminated in expected logarithmic time. Unfortunately, programmers today must typically build gossip protocols by hand—an approach that makes their programs more complicated and error-prone, and hinders attempts to optimize gossip implementations to achieve better performance. MiCA is a new system for building gossip-based management tools that are highly resistant to disruptions and make efficient use of system resources. MiCA provides abstractions that enable expressing gossip protocols in terms of functions on pairs of node states, along with a rich collection of composition operators that facilitates constructing sophisticated protocols in a modular style. The MiCA prototype realizes these abstractions on top of the Java Virtual Machine, and implements optimizations that greatly reduce the number and size of messages used.