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Python

Python

There are two recommended templates for Python 3 users.

Do you need to customise this template?

You can customise the official templates, or provide your own. The code for this templates is available on GitHub: openfaas/python-flask-template.

  • python3-http - based upon Alpine Linux, small image size, for pure Python only.
  • python3-http-debian - based upon Debian Linux, larger image size, required for native C modules as as SQL, Kafka, Pandas, and image manipulation.

Flask is used internally for handling HTTP requests and responses, however it is not exposed to the user, so is only an implementation detail.

The HTTP server used is currently Waitress.

This is an official template maintained by OpenFaaS Ltd.

Downloading the templates

Using template pull with the repository's URL:

faas-cli template pull https://github.com/openfaas/python-flask-template

Using the template store, since they are both within the same repository, either command will fetch down both templates.

faas-cli template store pull python3-http
faas-cli template store pull python3-http-debian

Using your stack.yml file:

configuration:
    templates:
        - name: python3-http

Python 3 versions

The python3-http template supports a dynamic Python version through a build argument.

It is recommended that you put the version within the OpenFaaS YAML file:

functions:
  postgres-fn:
    lang: python3-http
+    build_args:
+      - PYTHON_VERSION=3.12

The option can also be passed via a CLI flag, however this is not recommended as it is easy to forget or miss it:

faas-cli build --build-arg PYTHON_VERSION=3.11

Event and Context Data

The function handler is passed two arguments, event and context.

event contains data about the request, including: - body - headers - method - query - path

context contains basic information about the function, including: - hostname

Response Bodies

By default, the template will automatically attempt to set the correct Content-Type header for you based on the type of response.

For example, returning a dict object type will automatically attach the header Content-Type: application/json and returning a string type will automatically attach the Content-Type: text/html, charset=utf-8 for you.

Accessing Event Data

Accessing request body: 

def handle(event, context):
    return {
        "statusCode": 200,
        "body": "You said: " + str(event.body)
    }
Accessing request method:

def handle(event, context):
    if event.method == 'GET':
        return {
            "statusCode": 200,
            "body": "GET request"
        }
    else:
        return {
            "statusCode": 405,
            "body": "Method not allowed"
        }
Accessing request query string arguments:

def handle(event, context):
    return {
        "statusCode": 200,
        "body": {
            "name": event.query['name']
        }
    }
Accessing request headers:

def handle(event, context):
    return {
        "statusCode": 200,
        "body": {
            "content-type-received": event.headers.get('Content-Type')
        }
    }

Return a JSON body with a Content-Type

def handle(event, context):
    return {
        "statusCode": 200,
        "body": {"message": "Hello from OpenFaaS!"},
        "headers": {
            "Content-Type": "application/json"
        }
    }

Custom status codes and response bodies

Successful response status code and JSON response body

def handle(event, context):
    return {
        "statusCode": 200,
        "body": {
            "key": "value"
        }
    }

Successful response status code and string response body

def handle(event, context):
    return {
        "statusCode": 201,
        "body": "Object successfully created"
    }

Failure response status code and JSON error message

def handle(event, context):
    return {
        "statusCode": 400,
        "body": {
            "error": "Bad request"
        }
    }

Custom Response Headers

Setting custom response headers

def handle(event, context):
    return {
        "statusCode": 200,
        "body": {
            "key": "value"
        },
        "headers": {
            "Location": "https://www.example.com/"
        }
    }

Native dependencies

As explained in the introduction, only the Debian variant of the Python template is suitable for building native dependencies. Why? For one, many libraries are available as pre-compiled wheels, meaning they can be imported without any compilation. Secondly, Alpine Linux requires so many packages to be added to build code that it becomes larger than the Debian base. Thirdly, Alpine Linux is not compatible with many native libraries because it uses its own C library called musl.

If a pre-compiled wheel isn't available for your chosen package, then you can use a build option to add a build toolchain. Build options are an abstracted list of packages to install, grouped together.

functions:
  postgres-fn:
    lang: python3-http
+    build_options:
+      - libpq

The current list of build_options for the Debian-based template is available in the templates repository in the template.yml file. Pull requests and contributions are welcome, however packages can be specified even when they are not present as a build option.

Alternatively, individual packages within apt can be specified through build_args:

functions:
  postgres-fn:
    lang: python3-http
+    build_args:
+      ADDITIONAL_PACKAGE: "libpq-dev gcc python3-dev"

Example with Postgresql

stack.yml

version: 1.0
provider:
  name: openfaas
  gateway: http://127.0.0.1:8080
functions:
  pgfn:
    lang: python3-http-debian
    handler: ./pgfn
    image: pgfn:latest
    build_options:
      - libpq

Alternatively you can specify ADDITIONAL_PACKAGE in the build_args section for the function.

    build_args:
      ADDITIONAL_PACKAGE: "libpq-dev gcc python3-dev"

requirements.txt

psycopg2==2.9.3

Create a database and table:

CREATE DATABASE main;

\c main;

CREATE TABLE users (
    name TEXT,
);

-- Insert the original Postgresql author's name into the test table:

INSERT INTO users (name) VALUES ('Michael Stonebraker');

handler.py:

import psycopg2

def handle(event, context):

    try:
        conn = psycopg2.connect("dbname='main' user='postgres' port=5432 host='192.168.1.35' password='passwd'")
    except Exception as e:
        print("DB error {}".format(e))
        return {
            "statusCode": 500,
            "body": e
        }

    cur = conn.cursor()
    cur.execute("""SELECT * from users;""")
    rows = cur.fetchall()

    return {
        "statusCode": 200,
        "body": rows
    }

Always read the secret from an OpenFaaS secret at /var/openfaas/secrets/secret-name. The use of environment variables is an anti-pattern and will be visible via the OpenFaaS API.

Authenticate a function

To authenticate a function with a pre-shared secret, or API token, first create a secret, bind that secret to the function, then read it at runtime and validate it.

Create a new pre-shared secret:

openssl rand -base64 32 > python-auth-token.txt

Then create a new secret in OpenFaaS:

faas-cli secret create python-auth-token \
    --from-file python-auth-token.txt

Create a new function called python-auth:

faas-cli new --lang python3-http \
    python-auth

Bind the secret to the function:

version: 1.0
provider:
  name: openfaas
  gateway: http://127.0.0.1:8080
functions:
  python-auth:
    lang: python3-http-debian
+    secrets:
+    - python-auth-token

Now edit the function's handler.py file to read the secret and validate it:

def read_secret(name):
    with open("/var/openfaas/secrets/" + name) as f:
        return f.read().strip()

def handle(event, context):
    token = read_secret("python-auth-token")

    if not "Authorization" in event.headers:
        return {
            "statusCode": 401,
            "body": "Unauthorized"
        }

    if event.headers["Authorization"] != "Bearer {}".format(token):
        return {
            "statusCode": 401,
            "body": "Unauthorized"
        }

    return {
        "statusCode": 200,
        "body": "Access granted"
    }

Deploy the function with faas-cli up, then invoke it:

curl -i https://127.0.0.1:8080/function/python-auth \
    -H "Authorization: Bearer $(cat ./python-auth-token.txt)"

HTTP/2 200
Access granted

How to perform package upgrades at build time

The base images for the official OpenFaaS templates come from the Docker Hub, these images are built with automation and should always have the latest apk or apt packages installed.

That said, if you need to upgrade the images sooner, or are using an older image that was mirrored from the Docker Hub, you can add a --build-arg flag or build_args: entry in stack.yaml to force an upgrade on each build.

functions:
  fn1:
    lang: python3-http
    build_args:
      - UPGRADE_PACKAGES: "true"

faas-cli publish --filter fn1\
    --build-arg UPGRADE_PACKAGES=true

OpenTelemetry zero-code instrumentation

Using OpenTelemetry zero-code instrumentation for python functions requires some minor modifications to the existing Python templates.

There are two ways to customise a template:

  • Fork the template repository and modify the template. Recommended method that allows for distribution and reuse of the template.
  • Pull the template and apply patches directly in the ./template/<language_name> directory. Good for quick iteration and experimentation with template modifications. The modified template can not be shared and reused. Changes may get overwritten when pulling templates again.

Add the required packages for auto instrumentation to the requirements.txt file of the template:

opentelemetry-distro
opentelemetry-exporter-otlp

Update the Dockerfile to run the bootstrap command after the the template and function packages have been installed:

# Build the function directory and install any user-specified components
USER app

RUN mkdir -p function
RUN touch ./function/__init__.py
WORKDIR /home/app/function/
COPY --chown=app:app function/requirements.txt  .
RUN pip install --no-cache-dir --user -r requirements.txt
+ RUN opentelemetry-bootstrap -a install

The opentelemetry-bootstrap -a install command reads through the list of packages installed in your active site-packages folder, and installs the corresponding instrumentation libraries for these packages, if applicable. The OpenTelemetry Python agent uses monkey patching to modify functions in these libraries at runtime.

Update the fprocess ENV in the Dockerfile to start the OpenTelemetry agent:

# configure WSGI server and healthcheck
USER app

- ENV fprocess="python index.py"
+ ENV fprocess="opentelemetry-instrument python index.py"

Use your modified template to create a new function.

The OpenTelemetry agent can be configured using environment variables on the function:

functions:
  greet:
    lang: python3-http-otel
    handler: ./greet
    image: greet:latest
+    environment:
+      OTEL_SERVICE_NAME: greet.${NAMESPACE:-openfaas-fn}
+      OTEL_TRACES_EXPORTER: console,otlp
+      OTEL_METRICS_EXPORTER: none
+      OTEL_LOGS_EXPORTER: none
+      OTEL_EXPORTER_OTLP_ENDPOINT: ${OTEL_EXPORTER_OTLP_ENDPOINT:-collector:4317}
  • OTEL_SERVICE_NAME sets the name of the service associated with the telemetry and is used to identify telemetry for a specific function. It can be set to any value you want be we recommend using the clear function identifier <fn-name>.<fn-namespace>.
  • OTEL_TRACES_EXPORTER specifies which tracer exporter to use. In this example traces are exported to console (stdout) and with otlp. The otlp option tells opentelemetry-instrument to send the traces to an endpoint that accepts OTLP via gRPC.
  • setting OTEL_METRICS_EXPORTER and OTEL_LOGS_EXPORTER to none we disable the metrics and logs exporters. You can enable them if desired.
  • OTEL_EXPORTER_OTLP_ENDPOINT sets the endpoint where telemetry is exported to.

To see the full range of configuration options, see Agent Configuration