Back in 2015, I had just started at CANVAS Technology and my task was clear: to create a web application that can service many operations concurrently from users, robots, and other integration services. Prior to this new venture, I had spent my last few years doing Ruby on Rails, Node.js JavaScript, mobile applications (cordova, minimal Objective-C, Java/Android). Only a few months before joining CANVAS had I just started playing with Elixir and Phoenix. I was so excited and relieved to find something that was geared exactly for what we were embarking on.

What I want to outline in this post is the lessons I’ve learned using Elixir these last 3+ years and help others learn quickly.

Upgrade sooner than later

Discuss pains of upgrading Elixir 1.3 –> 1.6, Ecto 1.0 –> 2.0, Phoenix 0.9 –> 1.3. It definitely hasn’t been easy to update, this is mitigated by staying abreast of Elixir / phoenix changes and trying to implement early.

GenServers are your friend – but use them only if you must

Abstract away the API and the Server – link to post by Dave Thomas explaining splitting the APIs, Servers, and Implementations in Elixir.

Testing pains with GenServers and Ecto’s concurrency model

Make sure to restart genservers / supervisors. Having a connection time out be longer for longer running genservers that aren’t started every setup fixture.

Using docker for team / testing scenarios

Docker-compose for stack, testing with diff vars. Preload any databases by putting them in the postgres container root in /tmp.

Testing browsers with Hound / ChromeDriver

Use Hound and chromedriver.

Do not code everything to the Repo itself

It’s not as easy to cut off your database addiction. Having an intermediate context API that cache is a good first step.

PubSub is your friend, use structs to pass messages

When using cast/gproc, pass the Structs, don’t use tuples. Resist the simple solutiuons. Pass structs defined.

Learn ETS

Don’t use a cache when the Erlang VM has one built in.

Use behaviours

Take a look how crowdfundr app. Code to interfaces, not the implementations. Use the impl approach.

Nginx as a front-end for SSL termination

Links/discussion to the post, security wise, leave Nginx to handle the vulns and your app to handle the impl.

Releases with Distillery

Ship those tarballs, let it fly. Easier/safer than shiping your code. Should probably post about the replacing of ENV vars. Use a Config module for system set env variables instead of them getting baked into your sys.config file.

Clustering – using epmd / GenServers for node communication message passing

Link to swarm and libcluster – knowing that clustering comes out of the box with Erlang/Elixir.