Kollaps: Decentralized and Efficient Network Emulation for Large-Scale Systems

The performance and behavior of distributed systems is highly influenced by network properties, latency, bandwidth, packet loss, and jitter. When developing a distributed system, questions like, “how sensitive is the application’s performance to network latency and bandwidth?” commonly arise. Answering these questions systematically and in a reproducible manner is very hard due to the variability and lack of control over the network. Moreover, state-of-the-art approaches are focused exclusively on the control plane, lack support for network dynamics or do not scale beyond a single machine or small cluster, which further aggravates this problem. Kollaps is a distributed, scalable, and efficient network emulator addressing these limitations by hinging on two observations. First, from an application’s perspective, what matters are the emergent end-to-end properties (e. g., latency, bandwidth, jitter) rather than the internal state of the routers and switches leading to those properties. Second, this model is amenable to decentralized management, allowing the emulation to scale with the number of machines required by the application. This premise allows for building a simpler, dynamic emulation model that does not require maintaining the full network state. Kollaps is agnostic of the application language and transport protocol, scales to thousands of application nodes, and is accurate when compared against a bare-metal deployment or state-of-the-art approaches that emulate the full network state. We use Kollaps to accurately reproduce results from the literature and predict the behavior of complex unmodified distributed systems under different network dynamics.