Eucalyptus has a new and important milestone, as its private cloud technology goes fully open source with the forthcoming release of Eucalyptus 3.1.

Historically, the private cloud company had built its flagship (and proprietary) enterprise offering on top of an open source community edition.

Now the company is shifting to a services and support business model, and releasing one and only one platform – as open source.

Eucalyptus Systems made headlines a few months ago when it partnered up with Amazon Web Services for cloud portability. It was a significant event for the company and validation for its CEO Marten Mickoss, who has been a vocal  open cloud evangelist.

A blog entry by Mickos explains the change in approach to cloud development. Not only is Eucalyptus placing the code to its bread and butter on GitHub and opening its bug tracking to Jira, but it’s adopted a more open, agile development methodology internally.

“Eucalyptus 3.1 is the fourth software release we will issue in just 6 months. This is agile development at its best. We are serving highly demanding users all over the world, and it’s important to keep the pace up,” Mickos writes.

Mickos brags that during the development of Eucalyptus 3.1, the company spun out its Quality Assurance into a separate, dedicated team, with over half a million instances of Eucalyptus spun up just to test the platform. There’s also a new Eutester tool for customers to write and run their own test scripts. Worth noting is the fact that Mickos also says that a new Sustaining Engineering project at Eucalyptus headquarters is designed to maintain support for earlier releases of the platform, making sure that even large-scale customers stay up and running without being forced into an upgrade.

Eucalyptus has built a community around itself – Mickos claims that Eucalyptus sees 25,000 cloud starts per year, with over 240 business partners building unique value propositions on top of the platform. And for those who don’t want to actually fiddle with the source code itself, Mickos says that Eucalyptus will only expand its API support.

There’s a lot of chatter about Eucalyptus versus OpenStack in the private cloud market. In fact, at this week’s GigaOM Structure conference, Mickos and Chris Kemp, OpenStack project co-founder and CEO of Nebula, are slated to discuss the future of the open cloud (I’m bringing popcorn).

But the real thing to come away with here is the fact that in the cloud, open source, open standards and open APIs are the way forward. Mickos said as much at last week’s Cloud Expo in New York, and it’s something that OpenStack has recognized since day one.

The only real troublesome aspect here is that Eucalyptus has thrown its support wholeheartedly behind the Amazon EC2 API, which may currently be the de facto standard, but simply is not as open as AWS might want one to think. AWS still owns the standard, and any company that adopts it is ultimately beholden to Amazon’s mercy.