Microsoft today announced that it’s launching the Azure Functions event-driven computing service in preview. This marks the Microsoft cloud’s predictable entrance into a market that has gotten many developers excited, one that makes it easy to set up rules associated with their applications and then let the computers take action on their own.

Functions can be tied to triggers of events in the Azure — like the Azure IoT Suite — or other services. Developers don’t need to worry about scaling out these programs across many virtual machines, and they only pay for the time it takes for their functions to be executed.

“You can write this code in a wide variety of languages, including C# and Node.js,” Scott Guthrie, executive vice president for Microsoft’s Cloud and Enterprise group, said onstage today at Microsoft’s Build developer conference in San Francisco.

But there is a key differentiator here — relative to, for example, the Lambda service from public cloud market leader Amazon Web Services that kicked off this market or Google Cloud Platform’s Google Cloud Functions. What makes Azure Functions stand out is its open-source runtime that will allow companies to run it in their own data centers.

That’s not an unpredecented strategic choice, however. IBM’s Bluemix OpenWhisk is also open-source.

Even so, Microsoft will continue to execute on its strategy of taking its hyperscale-worthy services and making them available for on-premises deployment. That’s the whole point behind the Azure Stack portfolio of services.

But on the public cloud side, Microsoft has finally ported the Lambda hole.

The news isn’t a complete surprise, as Brad Sams of Petri reported last week on the existence of a landing page for Azure Functions.

A blog post on the new service is here.