How to Invoke a Lambda Function with AWS Signature Auth without Using Postman

Prerequisites

Before we dive into the instructions, make sure you have the following:

• An AWS account with a valid access key ID and secret access key.
• A Lambda function created in your AWS account.
• A programming language of your choice (we’ll use Python in this example).
• A code editor or IDE of your choice.

Step 1: Install the Required Libraries

In this example, we’ll use the `requests` and `botocore` libraries in Python to invoke our Lambda function using AWS Signature auth.

pip install requests botocore

Step 2: Set Up Your AWS Credentials

Set up your AWS credentials by creating a file named `~/.aws/credentials` with the following format:

[default]
aws_access_key_id = YOUR_ACCESS_KEY_ID
aws_secret_access_key = YOUR_SECRET_ACCESS_KEY

Replace `YOUR_ACCESS_KEY_ID` and `YOUR_SECRET_ACCESS_KEY` with your actual AWS access key ID and secret access key.

Step 3: Create a Lambda Function Client

Create a Python script with the following code to create a Lambda function client using the `botocore` library:

import boto3

lambda_client = boto3.client('lambda')

This code creates a Lambda function client using your AWS credentials.

Step 4: Create a Request to Invoke Your Lambda Function

Create a Python script with the following code to create a request to invoke your Lambda function:

import requests
import json
import hashlib
import hmac
import base64
import time

lambda_function_name = 'YOUR_LAMBDA_FUNCTION_NAME'
aws_access_key_id = 'YOUR_ACCESS_KEY_ID'
aws_secret_access_key = 'YOUR_SECRET_ACCESS_KEY'
region_name = 'YOUR_REGION_NAME'

# Create a request payload
payload = {'key': 'value'}

# Create a request headers
headers = {
    'Content-Type': 'application/json',
    'X-Amz-Target': 'Lambda.Invoke'
}

# Create a request URL
url = f'https://{region_name}.lambda.{aws_access_key_id}..amazonaws.com/2015-03-31/functions/{lambda_function_name}/invocations'

# Create a request method
method = 'POST'

# Create a request timestamp
timestamp = int(time.time())

# Create a request signature
message = f'AWS4-HMAC-SHA256\n{timestamp}\n{aws_access_key_id}/{region_name}/lambda/aws4_request\n'
message += hashlib.sha256(json.dumps(payload).encode('utf-8')).hexdigest()
signature = hmac.new(base64.b64decode(aws_secret_access_key), message.encode('utf-8'), hashlib.sha256).digest()
signature = base64.b64encode(signature).decode('utf-8')

# Create a request authorization header
authorization = f'AWS4-HMAC-SHA256 Credential={aws_access_key_id}/{region_name}/lambda/aws4_request, SignedHeaders=content-type;host;x-amz-date;x-amz-target, Signature={signature}'

# Create a request headers
headers.update({
    'Authorization': authorization,
    'X-Amz-Date': f'{timestamp}000000Z',
    'Host': f'{region_name}.lambda.{aws_access_key_id}.amazonaws.com'
})

# Send the request
response = requests.request(method, url, headers=headers, json=payload)

print(response.text)

Replace `YOUR_LAMBDA_FUNCTION_NAME`, `YOUR_ACCESS_KEY_ID`, `YOUR_SECRET_ACCESS_KEY`, and `YOUR_REGION_NAME` with your actual Lambda function name, AWS access key ID, secret access key, and region name.

Step 5: Invoke Your Lambda Function

Run the Python script to invoke your Lambda function using AWS Signature auth.

That’s it! You should now see the output of your Lambda function in the response.

Tips and Tricks

Here are some tips and tricks to keep in mind when using AWS Signature auth to invoke your Lambda functions:

• Make sure to use the correct AWS region and Lambda function name.
• Use a secure way to store your AWS access key ID and secret access key.
• Use a secure way to handle the request signature and authorization header.
• Test your code thoroughly to ensure it works as expected.

Conclusion

In this article, we’ve shown you how to invoke a Lambda function using AWS Signature auth without using Postman. By following these steps, you can programmatically invoke your Lambda functions using a programming language of your choice. Remember to keep your AWS access key ID and secret access key secure, and test your code thoroughly to ensure it works as expected.

Now, go ahead and take your AWS skills to the next level by exploring more advanced topics in Lambda function invocation and AWS Signature auth!

1. Using AWS Lambda with User-Managed Roles
2. Signature Version 4 Signed Request Examples
3. Boto3 Lambda Client

Frequently Asked Question

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