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Lab 3 - Introduction to Functions

Creating a new function

There are two ways to create a new function:

  • scaffold a function using a built-in or community code template (default)
  • take an existing binary and use it as your function (advanced)

Scaffold or generate a new function

To find out which languages are available type in:

$ faas new --list
Languages available as templates:
- csharp
- go
- go-armhf
- node
- node-arm64
- node-armhf
- python
- python-armhf
- python3
- ruby

Or alternatively create a folder containing a Dockerfile, then pick
the "Dockerfile" lang type in your YAML file.

At this point you can create a new function for Python, Python 3, Ruby, Go, Node, CSharp etc.

Hello world in Python

We will create a hello-world function in Python, then move onto something that uses additional dependencies too.

  • Scaffold the function
$ faas new --lang python hello-openfaas

This will create three files for us:

./hello-openfaas.yml
./hello-openfaas
./hello-openfaas/handler.py
./hello-openfaas/requirements.txt

The YAML (.yml) file is used to configure the CLI for building, pushing and deploying your function.

Note: Whenever you need to deploy a function on Kubernetes or on a remote OpenFaaS instance you must always push your function after building it.

Here's the contents of the YAML file:

provider:
  name: faas
  gateway: http://localhost:8080

functions:
  hello-openfaas:
    lang: python
    handler: ./hello-openfaas
    image: hello-openfaas

On the line image: make sure the name is prefixed with your Docker Hub account. For Alex Ellis this is image: alexellis2/hello-openfaas. Update this for your name every time you create a new function.

Here is the contents of the handler.py file:

def handle(req):
    """handle a request to the function
    Args:
        req (str): request body
    """

    print(req)

This function will just print the input, so it's effectively an echo function.

Edit the message so it prints hello world instead i.e.

    print("Hello World")

This is the local developer-workflow for functions:

$ faas build -f ./hello-openfaas.yml
$ faas push -f ./hello-openfaas.yml
$ faas deploy -f ./hello-openfaas.yml

Followed by invoking the function via the UI, CLI, curl or another application.

The function will always get a route, for example:

http://localhost:8080/function/<function_name>
http://localhost:8080/function/figlet
http://localhost:8080/function/hello-openfaas

Pro-tip: if you rename your YAML file to stack.yml then you will not need to pass a -f flag to any commands.

Functions can be invoked via a GET or POST method only.

  • Invoke your function

Test out the function with faas-cli invoke, check faas-cli invoke --help for more options.

Example function: space-counter

We'll create a function that pulls in a random name of someone in space aboard the International Space Station (ISS).

$ faas new --lang python space-counter

This will write three files for us:

./space-counter/handler.py

The handler for the function - you get a req object with the raw request and can print the result of the function to the console.

./space-counter/requirements.txt

This file lists any pip modules you want to install, such as requests or urllib

./space-counter.yml

This file is used to manage the function - it has the name of the function, the Docker image and any other customisations needed.

  • Edit ./space-counter/requirements.txt
requests

This tells the function it needs to use a third-party module named requests for accessing websites over HTTP.

  • Write the function's code:

We'll be pulling in data from: http://api.open-notify.org/astros.json

Here's an example of the result:

{"number": 6, "people": [{"craft": "ISS", "name": "Alexander Misurkin"}, {"craft": "ISS", "name": "Mark Vande Hei"}, {"craft": "ISS", "name": "Joe Acaba"}, {"craft": "ISS", "name": "Anton Shkaplerov"}, {"craft": "ISS", "name": "Scott Tingle"}, {"craft": "ISS", "name": "Norishige Kanai"}], "message": "success"}

Update handler.py:

import requests
import random

def handle(req):
    r = requests.get("http://api.open-notify.org/astros.json")
    result = r.json()
    index = random.randint(0, len(result["people"])-1)
    name = result["people"][index]["name"]

    print (name + " is in space")

Note: in this example we do not make use of the parameter req but must keep it in the function's header.

Now build the function:

$ faas build -f ./space-counter.yml

Tip: If you rename space-counter.yml to stack.yml then you can leave off the -f argument. stack.yml is the default file-name for the CLI.

Deploy the function:

$ faas deploy -f ./space-counter.yml

Invoke the function

$ echo | faas invoke space-counter
Anton Shkaplerov is in space

$ echo | faas invoke space-counter
Joe Acaba is in space

Troubleshooting: find the container's logs

You can find out high-level information on every invocation of your function via the container's logs:

$ docker service logs -f space-counter
space-counter.1.1e1ujtsijf6b@nuc    | 2018/02/21 14:53:25 Forking fprocess.
space-counter.1.1e1ujtsijf6b@nuc    | 2018/02/21 14:53:26 Wrote 18 Bytes - Duration: 0.063269 seconds

Troubleshooting: verbose output with write_debug

Let's turn on verbose output for your function. This is turned-off by default so that we do not flood your function's logs with data - that is especially important when working with binary data which makes no sense in the logs.

This is the standard YAML configuration:

provider:
  name: faas
  gateway: http://localhost:8080

functions:
  space-counter:
    lang: python
    handler: ./space-counter
    image: space-counter

Edit your YAML file for the function and add an "environment" section.

  space-counter:
    lang: python
    handler: ./space-counter
    image: space-counter
    environment:
      write_debug: true

Now deploy your function again with faas-cli deploy -f ./space-counter.yml.

Invoke the function and then checkout the logs again to view the function responses:

$ docker service logs -f space-counter
space-counter.1.1e1ujtsijf6b@nuc    | 2018/02/21 14:53:25 Forking fprocess.
space-counter.1.szobw9pt3m60@nuc    | 2018/02/26 14:49:57 Query  
space-counter.1.szobw9pt3m60@nuc    | 2018/02/26 14:49:57 Path  /function/hello-openfaas
space-counter.1.1e1ujtsijf6b@nuc    | 2018/02/21 14:53:26 Hello World
space-counter.1.1e1ujtsijf6b@nuc    | 2018/02/21 14:53:26 Duration: 0.063269 seconds

Make use of custom templates

If you have your own language template or have found a community template such as the PHP template then you can add that with the following command:

$ faas template pull https://github.com/itscaro/openfaas-template-php

...

faas new --list|grep php
- php
- php5

A list of community templates is maintained on the OpenFaaS CLI README page.

Now move onto Lab 4