Functions Framework for .NET

An open source FaaS (Function as a service) framework for writing portable .NET functions -- brought to you by the Google Cloud Functions team.

The Functions Framework lets you write lightweight functions that run in many different environments, including:

Google Cloud Functions
Your local development machine
Cloud Run and Cloud Run on GKE
Knative-based environments

Prerequisites

The Functions Framework for .NET requires the .NET Core SDK 3.1.

Quickstarts

Quickstart: Hello, World on your local machine

First, install the template package into the .NET tooling:

dotnet new -i Google.Cloud.Functions.Templates

Next, create a directory for your project, and use dotnet new to create a new HTTP function:

mkdir HelloFunctions
cd HelloFunctions
dotnet new gcf-http

That will create HelloFunctions.csproj and Function.cs in the current directory. Edit Function.cs to have a look at what's required, and provide a custom message if you want.

Run the function:

dotnet run

Once the server is running, browse to http://localhost:8080 to invoke the function. Press Ctrl-C in the console to stop the server.

Note:
Visual Studio supports using .NET Core CLI templates from version 16.8.0 onwards. In some versions (including 16.8.0) you first need to enable the feature under Tools / Options / Preview Features / "Show all .NET Core templates in the New project dialog". You will need to restart Visual Studio after enabling this feature.

Quickstart: Build a Deployable Container

Here is how to build and run a deployable container on your local machine.

Install Docker and the pack tool.

Build a container from your function using the Functions buildpacks:

pack build \
	--builder gcr.io/buildpacks/builder:v1 \
	--env GOOGLE_FUNCTION_SIGNATURE_TYPE=http \
	--env GOOGLE_FUNCTION_TARGET=HelloFunctions.Function \
	my-first-function

Start the built container:

docker run --rm -p 8080:8080 my-first-function
# Output: Serving function...

Send a request to this function by navigating to localhost:8080. You should see the output Hello, Functions Framework.

CloudEvent Functions

After installing the same template package described above, use the gcf-event template:

mkdir HelloEvents
cd HelloEvents
dotnet new gcf-event

That will create the same set of files as before, but the Function class now implements ICloudEventFunction<StorageObjectData>. This is a function that responds to CNCF Cloud Events, expecting data corresponding to a Google Cloud Storage object. If you deploy the function with a trigger of google.storage.object.finalize and then upload a new object to Google Cloud Storage, the sample event will log the details of the new event, including some properties of the storage object.

The procedure for running a CloudEvent Function is exactly the same as for an HTTP Function.

The type argument to the generic ICloudEventFunction<TData> interface expresses the type of data your function expects within the CloudEvent. The data type should be annotated with CloudEventFormatterAttribute to indicate an appropriate CloudEventFormatter which knows how to parse the CloudEvent, including its data. Typically this is a type from the Google.Events.Protobuf package. See the google-cloudevents-dotnet README for more information about this package.

Note:
Google Cloud Functions support for events predates the CNCF Cloud Events initiative. The types in the Google.Cloud.Functions.Framework.GcfEvents namespace provide payloads for these events. The Functions Framework converts the Google Cloud Functions representation into a CloudEvent representation transparently, so as a developer you only need to handle CloudEvents.

Untyped CloudEvent Functions

If you are experimenting with CloudEvents and don't yet have a payload data model you wish to commit to, or you want your function to be able to handle any CloudEvent, you can implement the non-generic ICloudEventFunction interface. Your function's method will then just be passed a CloudEvent, with no separate data object.

After installing the template package described earlier, use the gcf-untyped-event template:

mkdir HelloUntypedEvents
cd HelloUntypedEvents
dotnet new gcf-untyped-event

This will create a function that simply logs the information about any CloudEvent it receives.

VB and F# support

The templates package also supports VB and F# projects. Just use -lang vb or -lang f# in the dotnet new command. For example, the HTTP function example above can be used with VB like this:

mkdir HelloFunctions
cd HelloFunctions
dotnet new gcf-http -lang vb

The examples and documentation are primarily written in C# for the moment, but the same concepts and features apply equally to VB.

F# support is currently not "idiomatic F#", but regular F# functions should be easy to wrap using the code in the templates. Feedback on how we can provide a more familiar F# experience is welcome.

Run your function on serverless platforms

Google Cloud Functions

You can use the Google Cloud SDK to deploy to Google Cloud Functions from the command line with the gcloud tool.

Once you have created and configured a Google Cloud project (as described in the Google Cloud Functions Quickstarts and installed the Google Cloud SDK, open a command line and navigate to the function directory. Use the gcloud functions deploy command to deploy the function. For the quickstart HTTP function described above, you could run:

gcloud functions deploy hello-functions --runtime dotnet3 --trigger-http --entry-point HelloFunctions.Function

Other function types require different command line options. See the deployment documentation for more details.

Cloud Run/Cloud Run on GKE

Once you've written your function and added the Functions Framework, all that's left is to create a container image. Check out the Cloud Run quickstart for C# to create a container image and deploy it to Cloud Run. You'll write a Dockerfile when you build your container. This Dockerfile allows you to specify exactly what goes into your container (including custom binaries, a specific operating system, and more).

If you want even more control over the environment, you can deploy your container image to Cloud Run on GKE. With Cloud Run on GKE, you can run your function on a GKE cluster, which gives you additional control over the environment (including use of GPU-based instances, longer timeouts and more).

Container environments based on Knative

Cloud Run and Cloud Run on GKE both implement the Knative Serving API. The Functions Framework is designed to be compatible with Knative environments. Just build and deploy your container to a Knative environment.

Configure the Functions Framework

You can configure the Functions Framework using command-line flags or environment variables. If you specify both, the environment variable will be ignored. For convenience, if you specify just a single command line argument, that is assumed to be the target.

Command-line flag	Environment variable	Description
`--port`	`PORT`	The port on which the Functions Framework listens for requests. Default: `8080`
`--target` (or only argument)	`FUNCTION_TARGET`	The name of the target function (implementing `IHttpFunction`, `ICloudEventFunction` or `ICloudEventFunction<TData>`) to be invoked in response to requests.

If the function isn't specified at all, the assembly is scanned for compatible types. If a single suitable type is found, that is used as the function. If multiple types are found, the target type must be specified.

Examples:

dotnet run
dotnet run HelloFunctions.Function
dotnet run --target HelloFunctions.Function
dotnet run --target HelloFunctions.Function --port 8000

Further documentation

For more information, see the files in the docs directory.

brcaswell/functions-framework-dotnet