Most of Erlang applications requires configuration variables. It can be: database credentials, metrics report hosts, some system limits and so on. Such variables can be set in application resource configuration file. They can be accessed with `application:get_env`. You should prefer dynamic configuration instead of hardcoded one. But what if you need different properties in configuration depend on environment?

Assume you have your compound service, which uses database, some microservices and also sends push notifications to mobile phones. All these configuration properties rely on environment. You have different microservice hosts/ports, auth tokens, certificates, database passwords in production, staging and testing. You don’t use same credentials everywhere, do you? How to deal with it and handle configuration changes gracefully? (Quick hint, the most cool stuff is at the end of the article, so, if you don’t like reading the comparison of different ways – just skip it). Lets explore all options.

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