Building more reliable web applications with magic

Hubert Łępicki


About me

  • Hubert Łępicki
  • local guy
  • backup guy (not so great)
  • > 10 years programming
  • 2 daughters
  • part of awesome team at AmberBit

I work with web apps

Web apps suck




Speaking of the devil...

Some users have 13k notifications

What exactly happened?

  • One of the requests took time to process
  • it allocated a lot of memory
  • slow requests blocked web server
  • app become unresponsive for other users

The deployment

  • 2 x 2x Heroku Dyno (VM)
  • 8 unicorn web servers per dyno
  • 16 concurrent connections
  • this list sucks big time
  • 16 concurrent connections
  • 16 requests to block it all

Ruby reality

  • Ruby is slow
  • unicorn vs. puma
  • Ruby cannot into threads
  • there is no way to scale
  • this must be rocket science
  • must it?
  • why so painful?

Why making it work is hard?

  1. shared mutable data
  2. no built-in crash recovery mechanisms
  3. GC is hard
  4. threading is hard
  5. preempting is hard
  6. monitoring is hard

if only was there better VM

taking care of all those issues...

Edsger Dijkstra says...

  • famous dining philosophers problem
  • mutexes/semaphores
  • deadlocks
  • race conditions
  • spending too much CPU time in critical sections (wasting CPU power resources)

Let's discuss memory allocation

Shared heap is the source of all evil


  • LIFO structure
  • each function called adds stuff on top
  • each function finished removes stuff from top
  • VMs handle 1 stack per thread


  • shared memory between all threads
  • classes and types metadata
  • dynamically allocated memory

Heap of problems

  • global state
  • slow access by different CPUs/cores
  • need to synchronize access (locks, mutexes)
  • single point of failure
  • GC is a rocket science

Entirely different VM


  • exists since 1986
  • free and open source
  • proven in many battles
  • your telecom runs it

Simple concurrency

There is no shared memory

There is no problem synchronizing access to one

Multitask like a telecom box

  • multiple CPU cores required
  • message passing between processes
  • supervisors and crash recovery

Your web server in 2015

  • has multiple CPU cores
  • has tones of memory
  • is perfect hardware to run Erlang on

Why programmers avoid Erlang?

  • unfriendly syntax
  • unfamiliar terminology
  • different, functional mindset
  • requires writing a lot of code

José Valim

  • creator of many Ruby gems
  • long-time Rails contributor
  • frustrated with state of things
  • looked at Erlang
  • created new language that runs on top of Erlang VM
  • programmer-friendly language


Elixir is

  • dynamic programming language (with optional type checking!)
  • running on top of Erlang VM (beam)
  • integrates nicely into Erlang/OTP ecosystem
  • clean, easy to learn Ruby-like syntax
  • pattern matching
  • functional
  • immutable data structures
  • compiled

Great Unicode support

Source code documentation built-in


Testing framework


Automates common tasks


Manages dependencies


Talks to the databases


Serves web requests


Serves modern web apps

Phoenix Framework

Erlang tools


Writing code that writes code

Writing supervised code

Hardware failure

OTP app cluster

  • connect N nodes via (fast) web
  • concurrency / message passing just works
  • minimal changes to your code
  • yay, you wrote distributed app by accident
  • production-ready (remember dRB?)
  • failover
  • load balancing
  • sleep well

Zero-downtime deployments

  • elixir/erlang allows code hot-swapping
  • your app is modular
  • replace individual parts of system (applications)
  • do not miss a single message
  • do not loose a single HTTP request 

Less infrastructure is more

Ruby on Rails

  • [web] unicorn/puma + nginx/apache
  • [worker] resque
  • [scheduled tasks] cron + rake
  • [websockets] faye/pusher


[web] elixir

[worker] elixir

[scheduled tasks] elixir

[websockets] elixir

Application server

- bloat
+ speed





Thank you!


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