Looks like init function is called during the compile time

[oleg-kivra]

Hey,

I have a bit strange case for me. E.g. I can not override the settings with Application config. As far as I see it happens because the init function is called during the compile time, and options are just automatically passed to the call function. So to summarize I cant use configs in runtime in order to set different origins.

It looks like its a behaviour expected by Phoenix: https://hexdocs.pm/plug/Plug.html#c:init/1

The result returned by init/1 is passed as second argument to call/2. Note that init/1 may be called during compilation and as such it must not return pids, ports or values that are specific to the runtime.

[phasebash]

This might provide more context for what you are seeing? Can you confirm?
https://github.com/elixir-plug/plug/blob/40738527bbb45515d33b4030656703ddb0a84a6f/lib/plug/builder.ex#L37

[LukasKnuth]

I was just bitten by this as well. This isn't necessarily a problem with this plug, it's just the standard Phoenix config (see your config/compiletime/dev.exs file). The relevant config is plug_init_mode

We where running into this because we want to allow different origins based on the NAMESPACE environment variable set by Kubernetes. This configuration was in config/runtime.exs and worked as expected in test/dev.

On prod however, its completely ignored which makes debugging this issue very hard. I fixed it by using a function as the origin config and in that function loading our config at runtime.

It would be nice to add a note in the documentation pointing this out to people.