Workflows - a.k.a. functions calling functions

Building your first workflow - from OpenFaaS workshop

Using the CLI to deploy SentimentAnalysis function from the store:

mkdir $HOME/workflows
cd $HOME/workflows
faas-cli store deploy SentimentAnalysis

The Sentiment Analysis function will tell you the subjectivity and polarity (positivity rating) of any sentence. The result of the function is formatted in JSON as you can see with the example below:

echo -n "California is great, it's always sunny there." | faas-cli invoke sentimentanalysis
# Formatted result
  "polarity": 0.8,
  "sentence_count": 1,
  "subjectivity": 0.75

Now let's create a new simple function (like in the previous exercise) that will call sentimentanalysis just forwarding the request text.

faas-cli new --lang python3 invoker --prefix="<your-docker-username-here>"

The code should look like this:

import os
import requests
import sys

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

    gateway_hostname = os.getenv("gateway_hostname", "gateway")

    test_sentence = req

    r = requests.get("http://" + gateway_hostname + ":8080/function/sentimentanalysis", data=test_sentence)

    if r.status_code != 200:
        sys.exit("Error with sentimentanalysis, expected: %d, got: %d\n" % (200, r.status_code))

    result = r.json()
    if result["polarity"] > 0.45:
        return "That was probably positive"
        return "That was neutral or negative"

Put requests in requirements.txt file:

echo "requests" >> invoker/requirements.txt

Remember to set the environment variable gateway_hostname in invoker.yml:

version: 1.0
  name: openfaas
    lang: python3
    handler: ./invoker
    image: mircot/invoker:latest
      gateway_hostname: "gateway.openfaas"

Then, just deploy our function:

faas-cli up -f invoker.yml

You can now try to invoke the new function. You can verify that the request has been forwarded to sentimentanalysis by your custom function. We have just created a basic workflow.

$ echo -n "California is bad, it's always rainy there." | faas-cli invoke invoker
That was neutral or negative
$ echo -n "California is great, it's always sunny there." | faas-cli invoke invoker
That was probably positive


Example: using storage events webhook

If you are using Vagrant image you can start from here, otherwise at the end you'll find how to setup a S3 object storage on your own.

Let's configure it properly for using a webhook that points to our openfaas instance (we will use it later to trigger a function as soon as a new file appears).

mc admin config set local < /home/vagrant/config_minio.json
mc admin service restart local

The request sent to the function by Minio in case of a file upload will have a body in this form:

  "EventName": "s3:ObjectCreated:Put",
  "Key": "images/test7.jpg",
  "Records": [
      "eventVersion": "2.0",
      "eventSource": "minio:s3",
      "awsRegion": "",
      "eventTime": "2019-09-10T14:27:46Z",
      "eventName": "s3:ObjectCreated:Put",
      "userIdentity": {
        "principalId": "usernameID"
      "requestParameters": {
        "accessKey": "myaccesskey",
        "region": "",
        "sourceIPAddress": ""
      "responseElements": {
        "content-length": "0",
        "x-amz-request-id": "15C319FC231726B5",
        "x-minio-deployment-id": "f6a78fdc-8d8e-4d2c-8aca-4b0bd4082129",
        "x-minio-origin-endpoint": ""
      "s3": {
        "s3SchemaVersion": "1.0",
        "configurationId": "Config",
        "bucket": {
          "name": "images",
          "ownerIdentity": {
            "principalId": "usernameID"
          "arn": "arn:aws:s3:::images"
        "object": {
          "key": "test7.jpg",
          "size": 1767621,
          "eTag": "1f9ae70259a36b5c1b5692f91386bb75-1",
          "contentType": "image/jpeg",
          "userMetadata": {
            "content-type": "image/jpeg"
          "versionId": "1",
          "sequencer": "15C319FC2679B7CB"
      "source": {
        "host": "",
        "port": "",
        "userAgent": "MinIO (linux; amd64) minio-go/v6.0.32 mc/2019-09-05T23:43:50Z"

Now create two buckets called incoming and processed:

mc mb local/incoming
mc mb local/processed

Set the trigger for any new jpg file appearing in local/incoming:

mc event add local/incoming arn:minio:sqs::1:webhook --event put --suffix .jpg

You can log into the WebUI at http://localhost:9000/ui/ with username admin and password adminminio.

Minio login

From there you can upload files and check the contents of the buckets.

Minio login

Trigger a facedetect function on loaded images

First of all create a new function:

mkdir $HOME/triggers
cd $HOME/triggers

faas-cli new --lang python3 processimage --prefix="<your-docker-username-here>"

Then we need to modify the handler to:

  1. get the file name from the storage event
  2. get the file from the storage
  3. encode it in base64 (required as input by the face detection function)
  4. call the face detection function
  5. get the output and save it back to the storage in a separate bucket

A possible result could be:

import json
from minio import Minio
import requests
import os
import base64

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

    # Decode the json from the Minio event
    req = json.loads(st)

    # Get configuration parameters from the docker environment (set in the processimage.yml)
    gateway = os.getenv("openfaas_gw", "gateway.openfaas")

    # Configure the storage client
    mc = Minio(os.environ['minio_hostname'],

    # Set the name for the source and destination buckets 
    source_bucket = "incoming"
    dest_bucket = "processed"

    # Get the name of the file from the 'Key' field in the event message
    file_name = req['Key'].split('/')[-1]

    # Get the file from the storage
    mc.fget_object(source_bucket, file_name, "/tmp/" + file_name)

    # Encode the image into base64
    f = open("/tmp/" + file_name, "rb")
    input_image = base64.b64encode(

    # Pass it to the facedetect function
    r = + "/function/facedetect", input_image)
    if r.status_code != 200:
        return "Error during call to facedetect, expected: %d, got: %d\n" % (200, r.status_code)

    # Finally get the output and save it locally
    dest_file_name = f"processed_{file_name}"
    f = open("/tmp/" + dest_file_name, "wb")

    f = open("/tmp/input_" + file_name, "wb")

    # sync to Minio
    mc.fput_object(dest_bucket, dest_file_name, "/tmp/"+dest_file_name)

    return f"Image {file_name} processed. Result is in {dest_bucket}"

Now you need to configure the deployment of the functions:

version: 1.0
  name: openfaas
  # function for loading the image from storage - the code just edited
    lang: python3
    handler: ./processimage
    image: <your-docker-username-here>/processimage:latest
      write_debug: true
      # environment variables used inside the funcion code
      minio_hostname: ""
      minio_access_key: "admin"
      minio_secret_key: "adminminio"
      openfaas_gw: "http://gateway.openfaas:8080"

  # face detection function, pre-built. You can find the source here: 
    skip_build: true
    image: alexellis2/facedetect:0.1
      output_mode: "image"
      write_debug: true

Before pushing the function in, don't forget to set the requirements.txt:


Then just build and deploy our two functions with:

faas-cli build -f processimage.yml
faas-cli push -f processimage.yml
faas-cli deploy -f processimage.yml

Now, once the functions will be ready you should try to upload a .jpg image to the incoming bucket using the WebUI ( login at <your host>:9000 with user admin and password adminminio ) and soon you should be able to find a processed file in the processed bucket that you can download from the webUI and visualize.

In the following image you can see an example of the hook result:

Minio file upload

Minio file processed


  • Create a workflow with 2 functions in different languages
  • Try to create a workflow triggered by a storage event that use the Tensorflow serving function created on the previous set of homeworks

EXTRA: Setting up an S3-compatible storage

mkdir $HOME/minio_data
docker run -d -v $HOME/minio_data:/data --net host -e "MINIO_ACCESS_KEY=admin" -e "MINIO_SECRET_KEY=admindciangot"  minio/minio server /data

and the client

mv mc /usr/bin/mc
sudo chmod +x /usr/bin/mc