Google's live reloading application configuration: https://cloud.google.com/deployment-manager/runtime-configurator/
TL;DR:
Hey app, take your configs from <runtime_config_name>. The app can watch for those configurations and all variables inside of it and change without redeploying or restarting.
The workings are similar to using etcd as a configuration store. But it is more focused on app configuration in the design, variables inside of a config and support for watching and waiting for values and patterns