Can you change runtime config at runtime and is it evaluated. I read somewhere that runtime config is read at boot time

Questions / Help
1

Im trying to allow users set config at runtime but from what I’ve read so far it seems it cannot be done. Is that the case?

2

Check out Application.put_env/4 and see if that’s what you need.

3

thank you, I think this is what I need so if I use this function in release task then the values from this function should supercede those in runtime.exs ?

4

What Im trying to achieve is to load config values from a configs table in the DB.

The DB is not started at the time that runtime.exs is evaluated…

I tried something like this:
alias Dynamic.Repo
alias Dynamic.Structures.Config

Get config from DB and set it to the application

config = Config
|> Repo.all()
|> Enum.reduce(%{}, fn config, acc → Map.put(acc, config.key, config.value) end)

Then I tried setting the value with a value in config and fallback to ENV var

like so:

config :dynamic, Dynamic.PromEx,
grafana: [
host: config[“GRAFANA_HOST”] || System.fetch_env!(“GRAFANA_HOST”),
username: config[“GRAFANA_USER”] || System.fetch_env!(“GRAFANA_USER”),
password: config[“GRAFANA_PASSWORD”] || System.fetch_env!(“GRAFANA_PASSWORD”),
upload_dashboards_on_start: config[“UPLOAD_DASHBOARDS_ON_START”] || false
],
metrics_server: :disabled

5

You can do some or all of it in runtime.exs using environment variables. In your application’s start function, you can load config from files, the environment, etc. and use Application.put_env as @dimitarvp suggests.

defmodule My.Application do

  def start(_type, _args) do
    # set the config
    grafana_config = ....
    Application.put_env(:some_app, :key, grafana_config)

    # merge the config
    extra_some_config = ...
    existing_some_config = Application.get_env(:some_app, :some_config)
    Application.put_env(:some_app, :some_config, Keyword.merge(existing_some_config, extra_some_config)

    children = [...]
    # start the children
  end
end

To get it out of the repo, you’d have to start the Repo process first. You could try inserting a process in the children that starts after the repo but before promex and do the config in there.

Also check out Config Providers.

1 Like
6

Thank you both, this is just what I needed.