Why Phoenix is exciting for the modern web

Ruby on Rails is a server-side framework that makes it possible to write database driven web apps in days, instead of weeks. I’ve been a fan of Rails since I discovered it many years back.

Using Rails has however always meant sacrificing performance to gain developer productivity. Ruby is a slow language and apps can grow into big monoliths.

"Do things that are worse for the machine, that make programs run slower, but widen the smile on a programmer’s face.”

DHH, the creator of Rails about the Ruby programming language

The Phoenix Framework promises to be both fast and productive. What came as a surprise was a massive benefit of underlying technologies, the Elixir programming language and the Erlang Virtual Machine.

The Phoenix Framework

Phoenix appears on the surface to be similar to Rails. It’s a server-side MVC framework with same concepts such as migrations and generators. This makes it simpler for Rails developers to enter Phonenix.

Be aware though, the internals of Phoenix are very different.

Going real-time

Channels are the real-time layer built into Phoenix. The idea is that writing real-time apps should be trivial to implement.

Phoenix is optimised for multiple real-time connections, and said to handle 2 million concurrent connections on one machine at the same time.

"Channels is why I started the Framework.”

Chris McCord, creator of Phoenix

The amount of connected devices is increasing in the world, from smartphones to smart toasters. Phoenix is built for this brave new world.

There are already client libraries available for Web, Swift, ObjectC, Android and C# to communicate with Channels.

Modern front-end tools

Phoenix uses Node Package Manager (NPM) for client-side tooling. This is great as most front-end libraries are already available as an NPM package.

The default build tool is the little known Brunch. It works well out of the box, but can be skipped for using other build tools. Example:

mix phoenix.new —no-brunch

Phoenix promotes using ES6 for modern JavaScript and includes ready modules to talk with Phoenix back-ends. Example of importing sockets in JavaScript to communicate with Channels.

import sockets from phoenix

Live-reload is included in Phoenix by default, so every time a file is saved the page automatically updates in the browser.

Phoenix is not opinionated about CSS libraries or other front-end frameworks. You are free to pick yourself.


Phoenix is built with Elixir, a modern programming language created by José Valim in 2009.

Elixir is a dynamic, functional language. Functional means it has no classes, object instances or classic inheritance - leading to simpler code.

The syntax is nice and a lot can be accomplished in few lines of code. I recommend reading the Elixir website to learn more about the language features.

Elixir ships with a great set of tools to ease development. A build tool called Mix, Testing tool called ExUnit and an Interactive Shell called IEX.

Erlang Virtual Machine

Elixir is a compiled language, making it faster. The compiled code runs on the Erlang Virtual Machine. This is where the magic happens.

Erlang was built for telecom by Ericsson in 1986. It currently handles around 50% of the world telecom traffic.

A telephone network needs to operate regardless of the number of simultaneous calls, unexpected issues, or upgrades taking place. Those became Erlang’s design goals:

  • Concurrency
  • Distribution
  • Fault Tolerance
  • High Availability

These goal fit surprisingly well with the nature of the modern web.


The world is not synchronous. Many things are concurrently happening around you now while you read this.

The same is true for web apps. Modern web apps talk to multiple users, on multiple devices and perform multiple tasks, all at the same time.

Most platforms offer threads and background processes to deal with this kind of concurrency in a performant way. Developers know the complexity of using these technologies.

In Erlang concurrency is made simple by using light-weight processes within the virtual machine. Processes are an isolated unit and only communicate with each others by sending messages.

The Virtual Machine can spread load on multiple CPU cores on the same machine. It can actually harness the power of modern computers better than most other platforms.

Erlang can also easily be scaled to multiple machines, this brings us to the next section.


There is a debate in the software industry on whether to build big monoliths of code or smaller micro-services. Monoliths are simpler to build but don’t scale well.

Micro-services scale better but are more complex to maintain as complexity grows with every new service.

I’ve talked to number of companies that have started with monoliths, but forced to re-write parts of the system as a micro-service to scale and deploy in isolation from other parts of the system. One famous example is Twitter.

The Virtual Machine has an elegant solution to this problem. Since every process is an isolated unit and can communicate to the system on multiple machines, apps can be scaled infinitely. Yes infinitely. This blew my mind.

Fault Tolerance

Most programming languages run by default in one thread. For example NodeJS is asynchronous, but if something breaks it might take the whole system down.

Erlang has a concept of supervisors to deal with this. Supervisors monitor processes within the Virtual Machine. If a process goes down it will be restarted by its Supervisor without affecting other parts of the system.

In Erlang you should in general not write try-catch statements. Processes should just fail, log the problem and be restarted again. Making up a self-healing system.

High Availability

Because of Erlang built-in fault tolerance, systems have high availability. There is an example of long-running system in Erlang with 99.999999999% availability.

Because of Erlangs process model, it is possible to make zero downtime deploys. Updates are made live to production without taking the system down.


Phoenix takes good advantage of Elixir and Erlang features.

The Elixir programming language gives Phoenix an enjoyable developer experience and speed. Phoenix for example uses Elixir to compile HTML templates to bytecode to optmize speed further.

In Phoenix, each request and channel connection gets it’s own process within Erlangs Virtual Machine. This makes Phoenix great to build highly concurrent systems with good distribution mechanism, fault-tolerance and high availability.

It’s still early days for Phoenix. Many libraries are missing or immature compared to Rails. It’s ready for production and many companies are already using it live.

Services to deploy seem a bit immature for Phoenix. It can be deployed to Heroku in a simple way, but Heroku is still without support for Erlang’s concurrency features.

Deploying to your own setup requires time and skills. I trust that somewhere in the world hackers are sitting in a dark room, eating pizza and making this easier for the rest of us.

I’ve been greatly impressed by Phoenix and look forward to use it going forward.

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