The Plug.init/1 method gets called during the compile step and not during the startup like I thought, is there someway to update a plugs config when the router supervisor tree is being setup?

Background info: All of our applications/servers/api:s connect to a configuration server during startup and loads their config at that point, without the config the applications will not work since the configuration contains things like “How are the authentication rows formatted in redis”. The configuration can change depending on which datacenter the application will end up in so we can’t tell the application this during the compile step or by using environment variables.

Now, this was a easy problem to solve for most of our elixir apps, just add the configuration genserver to the top of the supervisor tree, it loads the config and the rest of the genservers can query it in their init/1 calls. Our only problem is the Plugs init/1 functions which are called during the compilation and we don’t have access to the configuration at that point. The config is a deeply nested, large (200 000 rows) map which means asking for the configuration rows each request might be too expensive.

We can of course just extract the plug functionality into a genserver but I would prefer to avoid the extra step if we could avoid it.