Building Scalable SystemsWhat you can Learn from Erlang

First Stop: 1973

Actor Model

• Carl Hewitt

Actor Model Principle

• An actor can:

• Send Messages to other Actors

• Create other Actors

• Process Next Message

Share Nothing

“An Island of Sanity in a Sea of Concurrency"

Actor

State

Actor

State

Actor

State

Actor

State

Actor

State

Naturally scalable

Next stop: 1986

Birth of ErlangJoe Armstrong, Robert Virding, Mike Williams, Bjarne Däcker

Share Nothing with Lightweight Processes

Let it Crash

Handle Failures with Process Links and Supervisors

Next stop: 1998

Erlang VM released as Open Source

Erlang strength lies in the VM

Vertical scaling: Multicore and Scheduler

Horizontal scaling: ClusteringTransparent, well almost

Erlang strengths match Server applications properties

• Server apps are most of the time IO bound

• Server apps are often memory bound.

NetworkStack

Accepted connections

Requests processingServer threads

Pool

Thread

Thread

Thread

Thread

Thread

Thread

Thread

Thread

Thread

…

ClientRequests

X

X

X

Connections Pooli.e. Apache

NetworkStack

Accepted connections

Requests processingLightweight processes

ClientRequests

…

One Connection per Thread

Erlang webservers i.e. Yaws, Cowboy, etc.

Design comparison

• Number of requests handled in peak time: 1Ks to 10ks

• Throughput: reduce quickly when max concurrency reached

• More complex code

• Number of concurrent requests handle in peak time: 100Ks to 1Ms

• Throughput: Higher for large number of concurrent requests.

• Simple code, no pool to manage

Design with worker thread pools Design with Erlang processes

Back to 2016

Erlang is still the Reference for Scalable Systems

Makes it easier to build Advanced Concurrency Patterns

New languages using the Erlang VM: Elixir, LFE, etc

Inspiration for new languages / Frameworks:

Go, Scala, Akka, Clojure, …

Next Stop ?