Building OpenFaaS Serverless function to detect weather using OpenWeatherMap and Python

Building OpenFaaS Serverless Python Function

Serverless computing is rapidly becoming famous for deploying applications and functions without the hassle of managing the underlying infrastructure. OpenFaaS is an open-source serverless framework for building functions with Docker and Kubernetes. This article will walk you through creating an OpenFaaS serverless function using Python to detect the current weather using the OpenWeatherMap API.

Table of Contents:


  1. OpenFaaS CLI installed
  2. Docker installed
  3. Python 3 installed
  4. An OpenWeatherMap API key

Setting Up Your OpenFaaS Environment

First, you need to set up an OpenFaaS environment. Then, follow the OpenFaaS documentation on deploying OpenFaaS on Kubernetes or Docker Swarm.

Creating the Function

Create a new directory for your function:

mkdir weather-function && cd weather-function

Generate a new Python function using the OpenFaaS CLI:

faas-cli new --lang python3 weather-function

This command will create a weather-function.yml file and a weather-function directory containing the function’s source code.

Update the requirements.txt file inside the weather-function directory to include the requests library:


Replace the content of the handler.py file inside the weather-function directory with the following code:

import json
import os
import requests


def handle(req):
        data = json.loads(req)
        location = data['query']['location']
    except (KeyError, ValueError):
        return json.dumps({"error": "Invalid request payload"})

    url = f"http://api.openweathermap.org/data/2.5/weather?q={location}&appid={OPENWEATHERMAP_API_KEY}&units=metric"
    response = requests.get(url)
    if response.status_code != 200:
        return json.dumps({"error": "Error fetching weather data"})

    weather_data = response.json()
    weather = weather_data['weather'][0]['description']
    temperature = weather_data['main']['temp']

    return json.dumps({
        "location": location,
        "weather": weather,
        "temperature": temperature

This function uses the requests library to fetch the current weather data from the OpenWeatherMap API based on the provided location.

Update the weather-function.yml file to include the OPENWEATHERMAP_API_KEY environment variable:


Replace YOUR_API_KEY with your actual OpenWeatherMap API key.

Deploying the Function

Build the function Docker image:

faas-cli build -f weather-function.yml

Push the function Docker image to a Docker registry (optional):

faas-cli push -f weather-function.yml

Deploy the function to your OpenFaaS environment:

faas-cli deploy -f weather-function.yml

Testing the Function

After deploying your function, you can test it by invoking it using the OpenFaaS CLI or sending an HTTP request to the function’s endpoint.

Using the OpenFaaS CLI:

echo -n '{"query": {"location": "San Francisco"}}' | faas-cli invoke weather-function

Using curl:

curl -X POST -d '{"query": {"location": "San Francisco"}}'

You should receive a JSON response containing the current weather data for the specified location:

  "location": "San Francisco",
  "weather": "clear sky",
  "temperature": 20

You can replace “San Francisco” with any location of your choice.


In this article, we demonstrated how to build an OpenFaaS serverless function that detects the current weather using the OpenWeatherMap API. By leveraging the flexibility and power of OpenFaaS and the simplicity of the OpenWeatherMap API, you can quickly develop and deploy serverless functions to address a wide variety of use cases. In addition, you can extend this example to include more features, such as fetching forecast data or integrating with other APIs to create a more comprehensive weather application.

Keep Learning: More on Serverless

Discover the world of serverless architecture in our comprehensive collection of articles! Equip yourself with valuable knowledge and skills in the exciting realm of serverless computing by exploring the following topics:

Don’t just stop there; continue your journey and delve even further into the fascinating and expansive world of serverless technologies and their endless possibilities.


Faizan Bashir

Principal Engineer | Architecting and building distributed applications in the Cloud | Adventurer

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