Containers, the concept that Docker implements, lets app developers give a self-contained environment for distribution. For devs that means consistency in deployments across environments, which in turn means sysadmins can deploy each of these apps as fully isolated units.
With that, you get really clean installs/updates/uninstalls, and your deployments get done with a well-defined, declarative definition file which can also handle multi service dependencies (a la Docker Compose/K8s)
Heh, crosspost