Rocket is a containerization model developed by CoreOS that serves as an alternative to Docker. As with Docker, CoreOS Rocket automates the deployment of applications as portable, self-sufficient containers that can run virtually anywhere on any type of server.
But while Docker has started to evolve into a complex platform that serves a variety of needs and functions, Rocket is designed to serve as a simple but secure re-usable component for deploying applications.
What Exactly Is Rocket?
CoreOS Rocket was created with four key areas of focus in mind: composability (all the necessary tools for operating containers need to be well integrated but independent), security, image distribution (simple and facilitated discovery of container images), and an open model.
At its most basic level, Rocket operates as a command-line tool, rkt, for running App containers, which are specifications of an image format, container runtime and a discovery mechanism. Rocket is oriented around the App Container Specification (appc), which CoreOS developed as a set of simple and open specifications for a portable container format.