Microsoft's embrace of open source software continues, with Azure Service Fabric making the first tentative foray into the open world. Today, the SDK was (mostly) published to GitHub under the MIT license. The team behind the move described it as the "beginning stages" of a wider use of open source.

Service Fabric, first revealed in 2015, grew out of the infrastructure Microsoft developed to build and run large-scale cloud services, including Azure SQL, Cortana, and Skype for Business. It provides scaling and fault tolerance for services, both stateless and stateful, running in containers across clusters of (virtual) machines. It runs in Azure, naturally, but the runtime is also freely downloadable and can be deployed across on-premises Windows systems, or even onto Windows virtual machines in non-Microsoft clouds. A Linux version of the runtime is currently in development, too.

Microsoft has already been using GitHub for tracking feature requests and bugs within Service Fabric. Users of the runtime have expressed a greater interest in the design and features of Service Fabric, and opening up the SDK is seen as the next step in engaging with the community and helping drive the development direction.

However, with Service Fabric, the company is being a lot more cautious than it has been with projects such as .NET or Chakra, the Edge browser's JavaScript engine. Part of this is due to history. Developed as an internal service, Service Fabric's development process uses tools that aren't public. To be publishable, such issues have to be resolved. Tools either need to be replaced or themselves published, and the service has to be cleanly extricated from any other systems that it depends on. Service Fabric is also mission critical to a great many services within Microsoft. These concerns would tend to promote a conservative, incremental approach to opening up the software.

This means that Service Fabric is stopping a long way short of the Platonic ideal represented by .NET Core, which is led by an independent oversight committee and which has all development done in the open on GitHub with a substantial number of community contributions. Microsoft isn't publishing the full Services Fabric SDK—support for reliable collections will be missing—and will initially develop privately, with occasional code pushes to the public source repository.

But although the team won't commit to any future course of action, it does hope to expand the reach of open source, with both further SDKs and even parts of the service runtime both potentially being candidates for future open sourcing.