I’ve been working on an Elixir application for the last year, and overall it’s been a smooth, pleasant experience. I’ve been meaning to write more, so here we go.

Hex, the package manager for Elixir is very well thought out, but there are things I’m still being introduced to, like private organizations. There’s a beta I’m trying out, and it requires me to use a hex org key, which is fine, but how do I securely store it in Heroku such that it’s available when installing packages?

My first attempt was to set the hook_pre_fetch_dependencies hook of the excellent buildpack for Heroku like so:

hook_pre_fetch_dependencies="mix hex.organization auth acme --key $HEX_ORG_KEY_FOR_ACME"

I pushed to Heroku and…

-----> Executing hook before fetching app dependencies: mix hex.organization auth acme --key

** (Mix) Could not invoke task "hex.organization": 1 error found!

--key : Missing argument of type string

Luckily, I had already set up a postdeploy script for Heroku’s app.json so I had that method in mind, however, there wasn’t a hook in that lifecycle that made sense for me to use. But, mixing the two approaches did seem like something worth trying, and this is what ended up working.

In ./bin/predeps


mix hex.organization auth acme --key "$HEX_ORG_KEY_FOR_ACME"

In elixir_buildpack.config


Worked, and feels clean enough!

- Jesse