Also, how do you manage your containers in production?
I'm not terribly fond of using environment variables for configuration, personally. That method requires either a startup shim or development work to make your program aware of the variables, and your container manager has to have access to all configuration values for the services it starts up.
Lots of people write their own scripts to do this; I wrote Tiller (http://github.com/markround/tiller) to standardise this usage pattern. While I have written a plugin to support storing values in a Zookeeper cluster, I tend to prefer to keep things in YAML files inside the container - at least, for small environments that don't change often. It just reduces a dependency on an external service, but I can see how useful it would be in larger, dynamic environments.
Management: We create AMIs using Packer. Packer runs a provisioning tool which downloads tho container and the configuration and sets up the process monitoring. It then builds a machine image, and then we launch new servers.