Microsoft currently support two versions of the Azure Functions runtime - version 1 and version 2. This post will look at the main changes between the two versions, and show you how you can check which runtime you’re using.

What are the key differences between versions?

Version 1 of the runtime was introduced back in 2016, when functions were first announced. At launch it supported JavaScript, C#, Python and PHP.

In late September 2018 Microsoft made the Functions 2 runtime generally available and with it bought a number of significant development, deployment and performance improvements including the ability to use the runtime anywhere - on a Mac or Linux machine too! It’s worth noting that as of March 2019, Python support for Functions 2 is still in preview.

There were significant under the hood changes made to improve performance - and .NET Core 2.1 support was added, alongside a move to .NET Core powering the functions host process instead of .NET.

Big changes were made to the way that bindings work - as part of 2.0 they became extensions instead of being bundled into the runtime itself (aside from HTTP and timer support which are deemed core to the experience). This means that some bindings didn’t make it over yet to the new 2.0 runtime - your mileage may vary, but the Microsoft bindings docs have a clearer comparison between the two.

There are also a bunch of new integrations with Functions 2 - for instance, Application Insights is supported with minimal configuration required, while you can easily use deployment centre to add code from other sources such as Github repos into your functions app.

How can I tell what runtime I’m using?

If you’re running a functions app on a Mac or Linux machine - there’s a fair chance you’re using the 2.0 runtime, as that’s what the functions command line tools support. You can verify this by opening the host.json file within the root directory of your app, which should look something like this:

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{    "version": "2.0",    "extensions": {      "http": {        "routePrefix": ""      }    } }

The version field directly references the version of the functions runtime you’re using. If it says 2.0, you’re using version 2 - if it’s 1 or missing completely, you’re on the first version of the runtime.

Similarly, you can also view the runtime for your app through the Azure Portal - open your app in the portal, then navigate to “Function app settings” where you’ll see the below “Runtime version” setting.