In most cases, configuration via environment variables works fine. There are cases where it doesn't. E.g. 10k pods restarting because of a simple config change

In most cases, configuration via environment variables works fine. There are cases where it doesn't. E.g. 10k pods restarting because of a simple config change is not ideal. Better subscribe to an external system like "etcd" fetch and update the config without restarting the process.