Proposal: Remote dynamic configurable elixir application

[Dan Calancea]

Let's suppose we have a elixir service that spawns some workers to do a job, the supervisor takes configuration from config and starts the workers. Now the classic way to configure such a project in prod is to use releases.exs, where you can configure environment variables and the release will reload the configuration.

What I want to implement now is a dashboard that will control multiple services configuration, this means that there should be a centralized storage for configuration and some kind of signaling when to change configuration.

Let's suppose we use postgres, some tables to store the configuration and custom signaling/ postgres NOTIFY to notify that the configuration has changed and needs to be reloaded.

The questions that arise are:

1. Is it possible/recommended to change the releases.exs file responsible for configuration in a release so that the new configuration is persisted across reloads?
2. Is it possible to implement this for dev environment? since as far as I know dev environment does not support runtime configuration currently.
3. Is it intended behavior that releases.exs replaces configuration added with Application.put_env/4 with option persistent: true?
   

[Jon Rowe]

Hi Dan

Attempting to answer question 2, the most recent version of elixir adds runtime.exs to replace/improve on releases.exs which runs at boot of an Elixir app from mix or a release, see https://hexdocs.pm/elixir/Config.html#module-config-runtime-exs

Cheers

Jon

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[José Valim]

In addition to what Jon wrote, it is worth keeping in mind that config/runtime.exs is mostly a wrapper around Application.put_env/4 with option persistent: true, as you well noted, so you can implement the functionality you need using those functions if necessary.

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[Dan Calancea]

Now the only question is: is it possible to restart elixir application programatically from code? I couldn't find any related documentation on this.

[José Valim]

You can call Application.stop and Application.start.

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