A hardware engineer look at code architecture.

Thomas Depierre

@Di4naO

DianaOlympos

@di4na

Twitter :

Github :

Slack :

Maths and Physics
Caml

Hardware (C, VHDL, ...)

Data Analysis

Elixir for fun

What is an engineer ?

Create a system that is a solution to a problem

How to create something that complex ?

How to create something that complex ?

  • Separation of concerns
  • Known reusable components
  • Clarke's third law

Any sufficiently advanced technology is indistinguishable from magic.

Clarke's third law

Why talk about it ?

  • Code is a possible solution to a problem

  • You build systems

  • Existing corpus about engineering, and not only about technological solution

    • Human Factors is an engineering field

  • Because as a Hardware engineer, OO never stuck in my original field

  • Because Erlang/OTP are an engineer solution

Erlang/OTP : for engineers

  • Find a solution for engineers to build systems with real constraints
  • Not a CS thing
  • Try, test, move or keep

I want to stay away from the obvious: ‘concurrency, yay!’ One thing I’m really interested in is how Elixir can help make architectural decisions easier.

George Guimarães, Plataformatec

Let's go into the real thing

Data in, transform, Data out

Let's have a look at OTP

Nothing about the outside world. Sorry.

Not really nothing no...

In

Well known structure. Decide the protocol

Transform

Ecto

Phoenix

Cowboy

...

OTP Behavio(u)rs

  • Separation of concerns :
    • independant
    • isolated
  • Known and reusable :
    • common interface
    • common callbacks
  • Magic :
    • Edge case handling done by experts
    • separation of concerns by abstraction

From top to bottom

  • Application

  • Supervisors

  • Process

    • gen_server

    • gen_statem

    • sys

    • ...

Application

  • Known component
  • Independant from your app
  • A full Service, battery included
  • Node level

In a factory, it is a service, a unit.

Supervisor

  • Put the workers at work!
  • Handle the dirty stuff : Who dies !
  • Orthogonal from your data flow
    • Kind of...
    • Linked to the structure of your app
    • But don't interact with the work being done

Just like in a Factory...

Process

  • Handle the data flow.
    • What goes where
    • How to transform
  • Respect the principles too, at a lower level
  • Hide their interiors through Client API

Your workers

Can be specific to your app or a known behaviour.

Hint: you probably want one of the generic behaviour

How to use it?

Think in term of service!

  • Is it used in more than one place ?
  • Does it handle it's own data ?
  • Is it modifying data ?
  • Could it be an independent piece of software ?

If you answer yes to any of these questions, you got a service.

How to use it?

Think in term of service!

  • Each of these piece get its own folder in /lib
  • Dedicated supervisor sub-tree
  • Define a struct for your data inside that service

Example_service

supervisor.ex

random_gen_server.ex

How to use it?

Think in term of service!

  • Each of these piece get its own folder in /lib
  • Dedicated supervisor sub-tree
  • Define a struct for your data inside that service

Example_service

supervisor.ex

random_gen_server.ex

Why use that architecture ?

  • You can extract that part easily later
  • Transform it into a library
  • or an application
  • or a dedicated node

Why use that architecture ?

You can even add an interface and get a microservice !

It is all the same thing. Define the business logic.

Use a layer of abstraction on top with a client API.

Supervisors

Supervisors are orthogonal to your data flow and business logic !

But not really

They define the boundaries of your services

They are helping in architecturing !

Common Gotchas

  • Ecto is not your app. It is a connection to the outside
  • Phoenix is not  your app. It is... a connexion to the outside ...

Common Gotchas

  • Supervisors are not here to handle data flow
  • Try to hide your OTP behaviours behind Client API
  • So please no GenServer.cast in the middle of code

Common Gotchas

  • Applications everywhere !!!
  • Put all your dependencies in applications
  • If you have multiple things, you can look at Umbrella.

Thank you for listening

Questions ?