This book aims to describe a superior approach to build heavily asynchronous and distributed applications based on the actor model. Major part of the book is about the elfo framework and is illustrated with best practices of its usage. The second part of the book tells you about the best corporate practices of asynchronous applications' architecture.


  • Assist in building fault-tolerant systems.
  • Be performant enough for low-latency systems.
  • Be observable, provide a lot of metrics to detect problems.
  • Provide built-in support of exposing log events, dumps, metrics, and trace events.
  • Distributing actors across several machines should be as simple as possible.


  • Provide the most performant way to communicate between actors.
  • Provide any HTTP server.


  • Asynchronous actors with supervision and custom life cycle.
  • Two-level routing system: between actor groups (pipelining) and inside them (sharding).
  • Multiple protocols: actors (so-called gates) can handle messages from different protocols.
  • Multiple patterns of communication: regular messages, request-response (TODO: subscriptions).
  • Config updating and distribution on the fly.
  • Appropriate for both low latency and high throughput tasks.
  • Tracing: all messages have trace_id that spread across the system implicitly.
  • Telemetry (via the metrics crate).
  • Dumping: messages can be stored for further debugging.
  • Seamless distribution across nodes TODO.
  • Utils for simple testing.
  • Utils for benchmarking TODO.