Skip to content

Create new functions


The OpenFaaS CLI has a template engine built-in which can create new functions in a given programming language. The way this works is by reading a list of templates from the ./template location in your current working folder.

Before creating a new function make sure you pull in the official OpenFaaS language templates from GitHub via the templates repository.

$ faas-cli template pull

This page shows how to generate functions in the most popular languages and explains how you can manage their dependencies too.

1.0 Go

To create a new function named go-fn in Go type in the following:

$ faas-cli new go-fn --lang go

You will now see two files generate:


You can now edit handler.go and use the faas-cli to build and deploy your function.

1.1 Go: dependencies

Dependencies should be managed with a Go vendoring tool such as dep.

$ go get -u
  • Initialise the dependencies
$ $GOPATH/bin/dep init
  • Now vendor a library

Make sure you're in the go-fn folder, now use dep ensure -add and the name of the library you want. In this example we are vendoring the package for use in our function.

$ dep ensure -add
  • Reference the package from function

You can now edit your function and add an import statement in handler.go to

2.0 Python 3

To create a Python function named pycon type in:

$ faas-cli new pycon --lang python3

You'll see:


Note: Python 2.7 is also available with the language template python.

2.1 Python: dependencies

You should edit pycon/requirements.txt and add any pip modules you want with each one on a new line, for instance requests.

The primary Python template uses Alpine Linux as a runtime environment due to its minimal size, but if you need a Debian environment so that you can compile numpy or other modules then read on to the next section.

2.2 Python: advanced dependencies

If you need to use pip modules that require compilation then you should try the python3-debian template then add your pip modules to the requirements.txt file.

$ faas-cli template pull
$ faas-cli new numpy-function --lang python3-debian
$ echo "numpy" > ./numpy-function/requirements.txt
$ faas-build -f ./numpy-function.yml

Step 11/17 : RUN pip install -r requirements.txt
 ---> Running in d0ff430a607e
Collecting numpy (from -r requirements.txt (line 1))
  Downloading (12.2MB)
Installing collected packages: numpy
Successfully installed numpy-1.14.2


3.0 Node.js

Generate a function named js-fn:

$ faas-cli new js-fn --lang node

You'll see:


3.1 Node.js dependencies

Node.js dependencies are managed with npm and the package.json file which was generated for you.

To add the cheerio module type in:

cd js-fn
npm i --save cheerio

You can now add a require('cheerio') statement into your function and make use of this library.

4.0 CSharp / .NET Core 2.1

You can create functions in .NET Core 2.1 using C# / CSharp.

  • Write a function named csharp-function
faas-cli new --lang csharp csharp-function

Now you can open your current folder in a tool such as Visual Studio Code and add dependencies using the project (csproj) file.

5.0 Ruby

Create a function called ruby-function:

$ faas-cli new --lang ruby ruby-function

The directory structure is:

├── ruby-function
│   ├── Gemfile
│   └── handler.rb
├── ruby-function.yml

Your code should be in the handler.rb file

5.1 Adding a Gem (Library)

Open the Gemfile in the ruby-function directory

Add the following line

gem 'httparty'

5.1 Using our Gem

Replace your handler.rb code with the following

require 'httparty'

class Handler
    def run(req)
        return HTTParty.get("{req}")

5.3 Building / Deploy / Run

Edit the ruby-function.yml and point your image to your dockerhub, for example ${your_user}/ruby-function

$ faas-cli up -f ruby-function.yml
Using bundler 1.16.4
Fetching multi_xml 0.6.0
Installing multi_xml 0.6.0
Fetching httparty 0.16.2
Installing httparty 0.16.2
Bundle complete! 1 Gemfile dependency, 3 gems now installed.
Bundled gems are installed into `/usr/local/bundle`
Post-install message from httparty:
When you HTTParty, you must party hard!

5.4 Invoke!

$ echo 'OpenFaaS' | faas-cli invoke ruby-function
   "quota_remaining" : 298,
   "quota_max" : 300,
   "has_more" : false,
   "items" : [
         "title" : "Scaling with GPU usage",
         "creation_date" : 1536315498,
         "answer_count" : 0,
         "view_count" : 10,
         "is_answered" : false,

6.0 Java

A Java 8 template is provided which uses Gradle 4.8.1 as a build-system.

Support is made available for external code repositories via the build.gradle file where you specify dependencies to fetch from repositories or JAR files to be added via the build.

  • Write a function java-function:
$ faas-cli new --lang java8 java-function
  • Write your code in:


  • Write junit tests in:


  • Update gradle config if needed in:

./build.gradle ./settings.gradle

  • Working with headers

You can use getHeader(k) on the Request interface to query a header.

To set a header such as content-type you can use setHeader(k, v) on the Response interface.

7.0 PHP 7

To create a PHP7 function named my-function type in:

$ faas-cli new my-function --lang php7

You'll see:


Add any dependencies/extensions as described below and implement your functions business logic in Handler.php.

7.1 Composer Dependencies

You should edit composer.json and add any required package dependencies, referring to the Composer Documentation for instructions on using composer.json.

7.2 Private Composer Repositories

Refer to the PHP7 Template Documentation for instructions on how to use Composers COMPOSER_AUTH environment variable to configure access to dependencies in private repositories.

7.3 PHP Extensions

The PHP7 template is based upon the Docker Library PHP image and provides the script which exposes the ability to customise extensions installed in a function image.

Refer to the PHP7 Template Documentation for instructions on customising installed extensions.

8.0 Customise a template

It is recommended that you use the official templates as they are provided and if there is a short-coming that you raise a GitHub issue so we can improve the templates for everyone.

All templates are driven by a Dockerfile and can be customised by editing the files found in the ./template folder.

8.1 Update the Dockerfile

There are several reasons why you may want to update your Dockerfile, just edit ./template/<language_name>/Dockerfile.

  • New base image - some companies prefer to use their own base images for Docker images for compliance, support or licensing reasons

  • Add native package - sometimes you may want to add a native package from the Alpine Linux repository or the Debian package repository - just add a step into the Dockerfile

  • Try a new version of a base-image - it may be that the project is showing support for Node.js LTS, but you want the cutting-edge version, you can do that too

8.2 Update a template's configuration

The name of a template is read from a "template.yml" file kept within the template folder: ./template/<language_name>/template.yml

For csharp we have the following:

language: csharp
fprocess: dotnet ./root.dll
  • language is the display name used for faas-cli new --list.
  • fprocess provides the process to run for each invocation - i.e. your function

8.3 Use your own templates

You can use your own Git repository for a custom or forked set of templates. This can be public or private.

See faas-cli template pull for more information.

ARM / Raspberry Pi

Templates for ARM and Raspberry Pi are provided on a best-effort basis. If you can help with maintenance please let the project contributors know.

  • ARMv7 / Raspberry Pi

Type in faas-cli new --list and look for any languages ending in -armhf. You can use any of these for your functions.

  • ARM64 / / Scaleway ARM 64-bit

For these platforms do the same as above and look for the -arm64 suffix.

It is easy to make your own templates so if you need to use this platform please convert one of the "regular" templates for your platform.