Docker, the open platform for developers to build, ship, and run distributed applications in software “containers”, now has a competitor which is challenging the direction Docker is taking and hopes to relegate it to the quayside.

San Francisco-based startup CoreOS, which is building a distribution of Linux tuned for containers, has  launched an open source software project called Rocket, claiming that its approach to managing containers will be true to the original path which Docker’s true-believers wanted it to follow.

Alex Polvi, the CEO and co-founder of CoreOS, has been a big fan of Docker since the early days, and told Wired. “We think that still needs to exist… so we’re doing something about it.”

Docker creator Solomon Hykes hit back on Ycombinator, saying “Competition is always good,” and promised that Docker would be “forced to up its game and earn its right to be the dominant tool”. But was heavily critical of CoreOS’ campaign: “‘Disappointed’ doesn’t even begin to describe how I feel about the behavior and language in [CoreOS’ announcement] and in the accompanying press campaign. If you’re going to compete, just compete! Slinging mud accomplishes nothing and will backfire in the end.”

Docker lost its way?

Docker has become popular in the enterprise world, with the likes of, Dell, HP, Google, IBM, Microsoft, VMware, Red Hat and others calling on the small start-up to partner with them.

CoreOS’s co-founder and CEO Alex Polvi sold his first startup Cloudkick to Rackspace for an estimated $30 million in 2010 at age of 25. Now at CoreOS he is making a Linux operating system that runs huge enterprise data centers more affordably, using less hardware by making use of containers.

However, in a recent blog Polvi wrote: “When Docker was first introduced to us in early 2013, the idea of a “standard container” was striking and immediately attractive: a simple component, a composable unit, that could be used in a variety of systems. The Docker repository included a manifesto of what a standard container should be. This was a rally cry to the industry, and we quickly followed.

“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: building images, running images, uploading, downloading, and eventually even overlay networking, all compiled into one monolithic binary running primarily as root on your server. The standard container manifesto was removed. 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.

“At CoreOS we have large, serious users running in enterprise environments. We cannot in good faith continue to support Docker’s broken security model without addressing these issues. Additionally, in the past few weeks Docker has demonstrated that it is on a path to include many facilities beyond basic container management, turning it into a complex platform. Our primary users have existing platforms that they want to integrate containers with. We need to fill the gap for companies that just want a way to securely and portably run a container.”

Docker makes an open source technology that allows developers to easily write apps in for a cloud world. Instead of giving each app a whole virtual machine to play with (with all the overhead that implies) Docker delivers applications in lightweight containers, which can be easily moved form development to operations and deployed at will. 

Docker Convention in Amsterdam

Vice president of marketing at Docker, David Messina, was more measured than Hykes, pointing out that Docker already has thousands of developers and “millions of users”. He added: “Docker has solved an incredible problem - dependency hell - in a way which is incredibly accessible, with strong principles around openness.”

Five hundred Docker developers are converging on Amsterdam this Thursday 4 December, for the second DockerCon - the first one in San Francisco in June presented Docker 1.0. This time round the event sold out two months before it opened, and could have been 100 percent bigger said Messina, already planning for an even bigger DockerCon back in San Francisco in June 2015.

DockerCon EU has been preceded by a security issue, as Docker users were told to install version 1.3.2 including urgent security updates, but the urgency arguably shows that Docker is being trusted for real work where security matters. 

Polvi has launched his pirate ship – but whether it will have the following wind of Docker remains to be seen. It is at a very early stage, and Docker may well (to pursue the nautical metaphor) have the weather gage.