As time goes on, I feel like this is anti-pattern. It's just convenient to have a global CONFIG which you can fetch anywhere some setting out of thin air. But really, I think we should just be parsing this in main and passing the respective configuration values to the part of the code which cares about them.

For example:

let cmd_args = config::AppConfig::parse()?;
let aws_config = config::load_aws_config(cmd_args.localstack_endpoint);
start_webserver(cmd_args.http_port, &aws_config);

Since this is already an established norm, I'm not going to block on it though.