# `Beamlet.Config.Provider`
[🔗](https://github.com/aaronrussell/beamlet/blob/v0.1.0/lib/beamlet/config/provider.ex#L1)

Reads a `config.exs` from the data dir when a release boots.

The file lets you configure a beamlet without rebuilding it. It is
a plain Elixir config file:

    import Config

    config :beamlet,
      policies: [
        explorer: [tools: [:eval]]
      ],
      eval: [timeout: 60_000]

It can set any of the keys `Beamlet.Config` lists. It is read after
all other config, so what it says wins.

> #### A policy here replaces the policy whole {: .warning}
>
> When the file names a policy, its version replaces any policy of
> the same name declared elsewhere. The two are not merged.
> Policies the file does not name are kept.

A change takes a restart. `beamlet policies.show` reads the file
afresh each time it runs, so you can check a change first. A
beamlet with no file starts as usual. A file that fails to
evaluate stops the boot with the file and line at fault.

The file stands alone: `import_config` and `config_env/0` do not
work in it.

## In your own release

The standalone server reads the file already. To read it in your
own release, add the provider to its `config_providers`:

    releases: [
      my_app: [
        config_providers: [
          {Beamlet.Config.Provider, path: {:system, "BEAMLET_DATA_DIR", "/config.exs"}}
        ]
      ]
    ]

`path` takes any path `Config.Provider` accepts. Point it at the
same directory as `:data_dir`.

# `read!`

```elixir
@spec read!(Path.t()) :: keyword()
```

Reads the file, returning what it declares.

Raises `ArgumentError` naming the file, and the line when the error
has one in it, so a boot log says where to look.

---

*Consult [api-reference.md](api-reference.md) for complete listing*