The open-source project for building cloud deployments began two years ago as a partnership between Rackspace and NASA and has blossomed to include more than 150 companies and more than 2,000 contributing developers. OpenStack reached a milestone on Thursday, with the fifth release of its software, code named Essex, which a variety of OpenStack supporters say brings the project to a new level of maturity, interoperability with other cloud providers and ease of use.

But cracks are starting to show.

Then, the first fissure came in late March when Eucalyptus, which is an open-source project for building private clouds, with Amazon Web Services that will expand interoperability between Eucalyptus' private clouds and AWS' public cloud services. The move threw the support of market leader AWS behind an project that is not OpenStack.

Then, this week came the "bombshell" as Gartner analyst Lydia Leong called it: Citrix announced it is bringing its cloud building platform named CloudStack -- which it purchased last year for a reported $200 million from Cloud.com -- into the Apache Software Foundation, in effect creating a competing open source model to OpenStack.

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