By now, you may have heard of a startup called Docker that has skyrocketed into prominence in less than two years, raising $55 million from several top tier VCs and angels like Yahoo founder Jerry Yang.On Monday, one of Docker's closest partners, another super-cool startup called CoreOS, stood up, said it didn't like the direction Docker was going, and launched an alternative technology.Before this, CoreOS was one of Docker's biggest fans.Docker has become so popular with software developers who have brought it into their companies, that big tech companies like Amazon, Dell, HP, Google, IBM, Microsoft, Red Hat, VMware and more have all called it up and begged the little 70-employee company to partner with them.On the other hand, you may not have heard of CoreOS. But it also has some major juice in the enterprise tech world. Its co-founder and CEO Alex Polvi sold his first startupCloudkick to Rackspace for an estimated $30 million in 2010 at age of 25.CoreOS makes a Linux operating system that runs huge enterprise data centers more affordably, using less hardware. In fact, it has none other than Greg Kroah-Hartman as its advisor. Kroah-Hartman is a rock star in the Linux world, one of the two top people leading Linux. (The other is Linux creator Linus Torvalds).CoreOS has such cache in its world that Google engineers, particularly in New York, have been leaving Google to work for CoreOS. Its New York office, obtained when it acquired Quay.io, is chock filled with ex-Googlers from New York, Polvi tells us.Until recently, CoreOS was all-in with Docker.Docker makes a free and open source technology that allows developers to easily write apps in a cloud world. Instead of writing one big app designed to live on one computer, like a server or a PC, Docker lets them mince up their app into tiny pieces.They wrap those pieces in a technology called a "container" and those containers easily plug in together. This lets an app be spread across lots of computers in the data center, which is how the cloud works. That's how an app can handle lots of users logging in from devices all over the world.CoreOS was basically building its tech to work with Docker. Co-founder and CTO Brandon Philips contributed so much code to Docker that he joined Docker's governance board.But on Monday, CoreOS came out swinging at Docker and launched an alternative called Rocket. It essentially didn't like all the new technologies that Docker was adding to its containers. Polvi wrote in a blog post: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. Brandon Philips, co-founder/CTO of CoreOS, became a top Docker contributor, and now serves on the Docker governance board. ...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.Polvi told Business Insider that he didn't condemn Docker for going in this direction. It's just that CoreOS really wants to keep that simple container simple."The key thing to take away about Rocket is that what Docker is doing is not a bad thing. It's just not what we signed up for. It's evolved into more than what we signed up for," he told us.It's not completely surprising that CoreOS has decided to take on Docker this way.CoreOS, which raised $8 million in the summer, used the money to buy a startup called bought Quay.io, then used that tech to launch something called a private "Docker repository" for enterprise customers. This is a tool that lets big organizations keep track of all Docker containers, the applets that work together to form an app. This kind of "private repository" is one of the ways that Docker earns its living, too. (Although CoreOS would argue that its product isn't an apples-to-apples comparison to what Docker is offering.)Still, within hours of discovering that its respected friend was gunning to be even more of a direct competitor, Docker released a blog post statement in response:Of course, different people have different views of how open source projects should develop. As noted above, the overwhelming majority of users, the vast majority of contributors, and the vast majority of ecosystem vendors want the project to support standard, multi-Docker container distributed applications. ... A small number of vendors disagree with this direction. ... In some cases, of course, there are technical or philosophical differences, which appears to be the case with the recent announcement from CoreOS regarding Rocket. We hope to address some of the technical arguments posed by the Rocket project in a subsequent post.Polvi also told us that eventually, Rocket and Docker should be able to co-exist, appealing to different customers.In the meantime, one thing is clear. The huge, shocking success of Docker is attracting others to the market and at least some of them, like CoreOS, have some serious engineering brainpower to bring to the game.We reached out to Docker for comment and will update when we hear back.SEE ALSO:This 28-Year-Old Sold His First Startup For $30 Million And Is Back With A Cool New CompanySEE ALSO:How An Awful, Misspelled Presentation Launched The Most Important Startup You've Never Heard OfJoin the conversation about this story Click here to read full news..