To the non-developer, it might feel like Docker containers just got started. But CoreOS — a major Docker-project contributor — is worried they're already going astray.

So, CoreOS has created its own format of Linux container, called App Container, and a prototype project named Rocket for running those containers.

The projects were announced Monday, coincident with the kickoff of DockerCon in Amsterdam.

There's more at stake than open source bragging rights. Docker Inc., the company curating the evolution of Docker containers, just raised $40 million, a fantastic sum for an open-source project less than two years old. I have to believe the money was backed by an assumption that Docker had become the de facto standard for containers and wasn't facing any immediate competition.

Weirdly, 18-month-old Docker Inc. is the "big" company here. In an online rebuttal to CoreOS, Docker Inc. CEO Ben Golub lists Docker's accomplishments so far, including support by every major public cloud and more than 700 contributors, 95 percent of whom do not work for Docker Inc. The bullet points do have the ring of an incumbent facing off against an upstart competitor.

"While we disagree with some of the arguments and questionable rhetoric and timing of the Rocket announcement, we hope that we can all continue to be guided by what is best for users and developers," Golub writes.

App Containers are at the heart of CoreOS' announcement. Rocket is the first software for running them — a "runtime," analogous to Docker Engine — but CoreOS told Wired that anyone else could build their own runtime as well.

CoreOS was bothered by the increasing complexity of Docker containers, writes CoreOS CEO Alex Polvi in a blog entry announcing Rocket. Docker's original vision was of simple, reusable containers, but plans for the future are more complex, including "tools for launching cloud servers, systems for clustering, and a wide range of functions" such as overlay networking, he writes.

"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," Polvi writes

App Containers, while apparently simpler, will have some added pieces of their own — things that CoreOS believes are missing from production Docker containers, such as security improvements.

Golub's rebuttal acknowledges one of the Docker add-ons in development: the orchestration of multiple containers together. But this kind of thing is being developed because it's where the Docker community wants to go, he writes.

"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 writes.

Details about these orchestration services are due to come out during DockerCon, he adds.

"This is all part of a healthy open-source process," Golub writes, noting that Docker Inc. plans to post more blog entries addressing the specifics of CoreOS' complaints.

Rocket 0.1.0 is available on Github.

(Photo by Steve Jurvetson on Flickr. Yes, that Steve Jurvetson. Creative Commons license; photo has been cropped.)