Why Erlang?

The post argues that Erlang is a better choice for concurrent network applications because it implements the actor model natively. It presents Wooga as a case where an Erlang backend handled similar game complexity with far fewer application servers than a Ruby backend.

Reading notes

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• Concurrency for web applications and API backends becomes more important as multicore CPUs become more common.
• Ruby developers discuss concurrency through threads, multiple runtimes, more processes, actor-model libraries like Celluloid, or Akka through JRuby.
• Actor-based approaches in Ruby, Python, and Java still depend on runtimes that do not natively support the model.
• In the actor model, actors run at the same time, communicate by messages, and do not share global state or shared memory.
• Because each actor owns its internal state, it can serialize access to that state and reduce deadlocks and race conditions.
• The actor model fits functional languages because they embrace immutable data.
• Erlang is described as a functional language that implements the actor model for concurrency.
• Erlang was developed by Ericsson for carrier-grade telecom switches, with goals of fault tolerance, high availability, and concurrent execution.
• The author says he had long been a Ruby developer but kept hitting limits in network applications such as web apps, web servers, and proxies.
• At Wooga, one Ruby backend for a large game ran on about 80 to 200 application servers and handled about 5000 to 7000 requests per second.
• A new backend for a similarly complex game was built in Erlang by Paolo and Knut and now uses about 1 application server, with 2 or 3 servers for redundancy.
• The backend uses a stateful design where each player is represented by an actor inside the Erlang VM.
• Requests for a player go directly to that actor, so many requests are answered quickly without hitting the database.
• If one actor crashes, the others are not affected because there is no shared or global state.
• When a player stops playing, the actor saves the game state to persistent storage and terminates.
• The author says Erlang spread to more backends and smaller services at Wooga after that success.
• He recommends learning Erlang by starting a small project and using learnyousomeerlang.com rather than only reading books.