After years of battling Linux as a competitive threat, Microsoft is now offering Linux-based operating systems on its Windows Azure cloud service.

The Linux services will go live on Azure at 4 a.m. EDT on Thursday. At that time, the Azure portal will offer a number of Linux distributions, including Suse Linux Enterprise Server 11 SP2, OpenSuse 12.01, CentOS 6.2 and Canonical Ubuntu 12.04. Azure users will be able to choose and deploy a Linux distribution from the Microsoft Windows Azure Image Gallery and be charged on an hourly pay-as-you-go basis.

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In Suse's case, Azure users will be able to provision the latest edition of either the Suse Linux Enterprise Server or OpenSuse. "To set up an instance, they just pick the Suse enterprise image and provision it like they would on any other cloud service," said Doug Jarvis, Suse product marketing manager for Cloud. Suse can automatically update these virtual distributions with security patches, bug fixes and new features.

Azure users will also deploy applications they've built with the Suse Studio IDE (integrated developer environment) directly onto Azure. In this case, they do not need to worry about the machine image. Instead, they will enter their Azure ID into Suse Studio before deploying their application to the Azure cloud.

The move may be a surprising one for observers of Microsoft, which has traditionally considered itself a platform company, built around the enormous success of Windows. As such, the company has traditionally seen Linux as a competitive threat, especially in the server market, where it competes with Windows Server for replacing traditional Unix servers.

With its Azure cloud service, however, Microsoft faces a formable rival in the popular Amazon Web Services -- which offers Linux distributions such as Canonical Ubuntu and Red Hat Enterprise Linux in addition to Windows.

"We do find it to be a watershed moment, especially considering the past, but it's not surprising," said Amanda McPherson, vice president of marketing and developer services at The Linux Foundation, in an email interview. "Cloud computing has mostly been a Linux and open-source affair. Microsoft is a smart company and will do what they need to do to be a player in cloud, and in this case it means doing something that was anathema in its past: agreeing that another operating system is needed in order to be technically relevant. I'm sure many Redmond inhabitants aren't too happy about this, but it's good for users."

Over the past year, Microsoft engineers have done considerable work on ensuring the driver for its Hyper-V Windows-based hypervisor works with Linux, the underlying hypervisor for Azure. As part of an earlier cooperative agreement with Suse, Microsoft has also worked quite a bit with Suse on adapting Linux to work on Hyper-V.

"Microsoft recognizes that their customers run more than just Windows in their enterprise, and this is an opportunity for Windows Azure to run as many workloads as possible," said Wade Wegner, chief technology officer for Aditi Technologies, a technology services company and Microsoft partner. "The cloud provides a way to make it easier to connect all of these different platforms and technologies, and my take is that Microsoft is trying to make Windows Azure the best and simplest place to run your applications regardless of the platform or technology."

The partnership may benefit Linux as well.

"There are customers who view Microsoft as their principal IT provider, and they will want to work with Microsoft," said Peter Chadwick, Suse senior product manager for cloud operations. "We've been working with Microsoft on interoperability, so this is a logical extension to that."

Open-source support company OpenLogic is providing CentOS for the Azure portal. CentOS is a clone of the enterprise-focused Red Hat Enterprise Linux distribution. (Red Hat did not respond to queries to comment on the Azure announcement.) OpenLogic has provided commercial support for CentOS since 2009, along with 600 other open-source programs. For Microsoft, OpenLogic will support all the running instances of CentOS, which includes providing Azure with the latest version of CentOS. Users will be able to update their CentOS virtual machines from a repository of patches that OpenLogic will maintain on Azure. Microsoft has contracted OpenLogic to provide support, initially, for a set monthly fee, said Steve Grandchamp, CEO of OpenLogic.

The Linux virtual machines are now offered in technology preview mode, so pricing has not been announced. The images will be persistent, meaning they can be shut down and reopened without loss of data. In addition to the virtual machine images of selected distributions, users will be able to import their own Linux builds through Microsoft's Virtual Hard Disk (VHD) capability, according to the announcement posted by Microsoft.

The release also mentions that Azure now supports both Python and Java, as well as Web development technologies such as Node.js and PHP, which will pave the way for easy use of Web content management tools such as WordPress, Drupal and Joomla.

Joab Jackson covers enterprise software and general technology breaking news for The IDG News Service. Follow Joab on Twitter at @Joab_Jackson. Joab's e-mail address is Joab_Jackson@idg.com