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Rocket Containers, an Alternative to Docker, Blasts Off

CoreOS, in announcing the move, says that Docker has lost sight of its core mission of providing simple application containers.

• By Keith Ward
• 12/02/2014

One vendor, though, thinks Docker is getting too big -- as in too complex, too unwieldy, too far from its original mission. That's why CoreOS just announced a new container technology – Rocket – that it believes will be what Docker was supposed to be before it got so big.

CoreOS is a lightweight, Linux-based operating system for enterprise environments, delivered as a service. CoreOS applications run in Linux containers powered by Docker. But that appears to be changing, according to a post by CoreOS CEO Alex Polvi. Rocket was released yesterday as a prototype on GitHub.

Too Many Tools?
In his post, he explains his disenchantment with the direction Docker's heading:

"Unfortunately, a simple re-usable component is not how things are playing out. Docker now is building tools for launching cloud servers, systems for clustering, and a wide range of functions … We should stop talking about Docker containers, and start talking about the Docker Platform. It is not becoming the simple composable building block we had envisioned." 

To that end, Povli announced Rocket 0.1.0. He calls Rocket a "command line tool for running App Containers." The container has three parts: an image format, runtime and discovery mechanism.

A 'Broken Security Model'
Povli also had some harsh words for Docker, saying that "We cannot in good faith continue to support Docker's broken security model, " referring to the fact that Docker runs everything through a central daemon. He added that "We need to fill the gap for companies that just want a way to securely and portably run a container."

Although the timing of the Rocket announcement may be coincidental, it's worth noting that DockerCon Europe is being held this week in Amsterdam, the Netherlands. That fact was not lost on Docker CEO Ben Golub, who responded to Povli's blog with thoughts of his own. "… we disagree with some of the arguments and questionable rhetoric and timing of the Rocket announcement … " he stated on the Docker blog.

Docker CEO: Changes Are Due to Market Forces
Golub said that the growth of Docker was a response to the reality of the market:

"While Docker continues to define a single container format, it is clear that our users and the vast majority of contributors and vendors want Docker to enable distributed applications consisting of multiple, discrete containers running across multiple hosts."

Golub said that he'll have more to say about Rocket in a future post. "For now, we want to emphasize that this is all part of a healthy, open source process. We welcome open competition of ideas and products." He added that Docker users don't have to extend it; it can be used as nothing more than a simple container.

Container Wars?
The Rocket announcement is the latest salvo in what appears to be the beginning of a container war. Microsoft, for example, recently said it's adding Docker support to Windows. Microsoft is going even further, though, developing its own version of Windows containers in a project code-named "Drawbridge." In fact, Microsoft has used Drawbridge internally, and has made it available, on a limited basis, in its Azure cloud platform.

The Rocket prototype can be found here.