Including data files in a Distillery release

The traditional place to put non-code resources that are needed at runtime is the priv folder. All the tools are aware of this convention and preserve proper paths.

You can access the files at runtime using Application.app_dir(app_name, "priv/path/to/file")

Thank you @michalmuskala. I’m going to try this and report back!

EDIT: Michal’s answer does work. Marking it as the solution.

You can use :code.priv_dir(app) to get the priv directory directly as well, it’s what I typically use in my applications.

How can I access the priv path in dev.exs file? When I do it as below:

"#{Application.app_dir(:app)}/priv/ssl/ca.pem"

I got:

** (Mix.Config.LoadError) could not load config config/dev.exs
    ** (ArgumentError) unknown application: :app
    (elixir) lib/application.ex:428: Application.app_dir/1
    (stdlib) erl_eval.erl:670: :erl_eval.do_apply/6
    (stdlib) erl_eval.erl:269: :erl_eval.expr/5
    (stdlib) eval_bits.erl:81: :eval_bits.eval_field/3
    (stdlib) eval_bits.erl:65: :eval_bits.expr_grp/4
    (stdlib) erl_eval.erl:474: :erl_eval.expr/5
    (stdlib) erl_eval.erl:878: :erl_eval.expr_list/6
    (stdlib) erl_eval.erl:236: :erl_eval.expr/5

I’m setting ssl_opts for Ecto, putting those pem files under priv/ssl, but the application can’t access them after building with Distillery.

Quick question about this: Does this directory stay the same for all releases, or will each new version have its own priv_dir?

As long as you install each release into the same directory then the priv directory ‘should’ always remain the same (unless using a custom OTP build or so).

New versions of your application will have a slightly different path (as the path includes the version of your app in a release), but the same version will always be the same path, regardless of OTP version, Elixir version, etc.

Thank you. This has tripped me off before. I stored some general app-state-information in a file (because the database would be ridiculously overkill for this), but it turned out that the file was not found after upgrading my release, with the app thus restarting with a blank slate every time after an upgrade.

Yeah my general advice along these lines is to use priv for anything version-specific and/or static data/assets and to rely on something more well-known of your own creation in the filesystem for stateful data, i.e. /var/myapp/. You could also use the var directory created by the release, which you can obtain via the RELEASE_MUTABLE_DIR environment variable exposed to the release (which is used for temporary files like pipes, generated configs, and log files). That said, I would still tend towards using a directory like /var/myapp myself, since you can avoid clutter and manage it’s permissions and so on separately.

I’m having the same problem as @chensan I’m trying to set some ssl_opts in a config file and it says:

** (ArgumentError) unknown application: :app
    (elixir) lib/application.ex:654: Application.app_dir/1
    (elixir) lib/application.ex:681: Application.app_dir/2
    (stdlib) erl_eval.erl:680: :erl_eval.do_apply/6
    (stdlib) erl_eval.erl:888: :erl_eval.expr_list/6
    (stdlib) erl_eval.erl:240: :erl_eval.expr/5
    (stdlib) erl_eval.erl:232: :erl_eval.expr/5
    (stdlib) erl_eval.erl:888: :erl_eval.expr_list/6
    (stdlib) erl_eval.erl:240: :erl_eval.expr/5

The app is named :app in mix.exs