Overview:
Create a simple API that returns current weather information for a given city using AWS Lambda, API Gateway, and OpenWeatherMap API.
An API (Application Programming Interface) is a set of rules that allows two software applications to communicate with each other.
Tools & Skills Involved:
AWS Lambda (Python runtime)
Amazon API Gateway
IAM Roles & Permissions
OpenWeatherMap API (free tier)
Python (requests library)
Postman or browser for testing
Powershell
Step 1: Sign Up for OpenWeatherMap
Go to https://openweathermap.org/api
Sign up and get your free API key.
Step 2: Create Your Lambda Function
Go to AWS Console > Lambda > Create Function.
Choose: “Author from scratch”
Runtime: Python 3.x
Name: weather-api-lambda
Click create
Step 3: Add Your Lambda Code
code:
Step 4: Add Environment Variable
Go to your AWS Lambda function.
Scroll down to Environment variables.
Click Edit, then Add environment variable:
Key: WEATHER_API_KEY
Value: (Your API key from OpenWeatherMap)
Step 5: Add Permissions for Internet Access
Attach an execution role with AWSLambdaBasicExecutionRole
Ensure Lambda is in a VPC that allows internet access (or no VPC for easier setup).
Check if Your Lambda Is in a VPC
Go to the Lambda Console
Open your function
Scroll to the "Configuration" > "VPC" section
If it says "Not attached to any VPC", your Lambda already has internet access
Step 6: Create API Gateway
Go to API Gateway > Create API > HTTP API > Click Build
Choose integration → Select Lambda
Select your Lambda function from the dropdown
Click Next
Method: GET
Resource path: /weather
Create a stage name — e.g., APIweather
Click Next, then Create
Step 7: Deploy & Test
Deploy the API
Test your endpoint with:
https://olxheqwg4c.execute-api.us-west-2.amazonaws.com/
I tested the endpoint URl and got this.
That is my base endpoint, but it doesn't tell us which route or resource path is configured. That’s why you’re getting:
{"message":"Not Found"}
Lets fix this error.
Check Your Lambda Integration Path:
If it's an HTTP API:
Click Routes
You’ll see something like: ANY /weather or GET /
Note the full path (e.g., /weather)
I found the error and the correct path which includes a stage name, but it's not working without it, here's exactly how to fix and use the full correct URL:
Breakdown of Your Components
Base endpoint: https://olxheqwg4c.execute-api.us-west-2.amazonaws.com
Stage name: APIweather
Route/Path: /weather-api-lambda
Query string: ?city=Lagos
This is the correct URL PATH:
https://olxheqwg4c.execute-api.us-west-2.amazonaws.com/APIweather/weather-api-lambda?city=Lagos
My API Gateway is correctly connected to your Lambda function,
But my Lambda function isn't running the weather fetching logic yet — it's still using the default "Hello from Lambda!" response.
I need to replace the "Hello from Lambda!" code in your function with the weather-fetching logic.
Open PowerShell
Press Windows + R, type powershell, and hit Enter.
Create the project folder on your local computer/desktop
mkdir lambda-weather
cd lambda-weather
Create the Python file
In the same terminal: notepad lambda_function.py
Here is the lambda code scripted inside
Save and close the notepad.
Install the requests package locally
In the same PowerShell window: pip install requests -t .
Zip everything
Still inside the lambda-weather folder: Compress-Archive -Path * -DestinationPath lambda-weather.zip
Upload to Lambda
Go to AWS Lambda console.
Choose your function.
Click Upload from → .zip file.
Select lambda-weather.zip.
Click Deploy.
Test the Function Directly (Optional)
I ran a test before setting up API Gateway:
- Click the Test tab in Lambda
- If it works, you’ll see a 200 OK response with weather data.
Test the API via Browser:
https://olxheqwg4c.execute-api.us-west-2.amazonaws.com/APIweather/weather-api-lambda
There you go
Brief Discussion
What problem did I solved getting weather info: I built a serverless solution to fetch real-time weather data using AWS Lambda and API Gateway. The problem was accessing weather info by city without managing servers. Now, users can get live forecasts by simply hitting a public API endpoint.
How API Gateway & Lambda work together: API Gateway acts as the front door, receiving HTTP requests and passing them to AWS Lambda. Lambda runs backend code in response, processes the request, and sends back a result. Together, they enable scalable, serverless APIs without managing servers.
How this demonstrates serverless and cloud-native skills: This project shows serverless and cloud-native skills by using AWS Lambda to run code without managing servers and API Gateway to expose it as a RESTful API. It demonstrates event-driven design, scalability, cost-efficiency, and integration of cloud services.
This project demonstrates the power of serverless architecture using AWS Lambda and API Gateway to build a scalable weather information API. It showcases my ability to integrate third-party APIs, handle cloud deployments, and write clean, resilient code.
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