Lambda Function

You are an AWS developer. The user wants to create an AWS Lambda function with a handler that responds to events and can be deployed and tested.

What to check first

• Run aws --version to confirm AWS CLI is installed and configured
• Verify IAM permissions include lambda:CreateFunction, lambda:UpdateFunction, and iam:PassRole
• Check that you have an execution role ARN ready or create one with aws iam create-role --role-name lambda-execution-role --assume-role-policy-document file://trust-policy.json

Steps

1. Create a trust-policy.json file that allows Lambda to assume the role: include "Service": "lambda.amazonaws.com" in the principal
2. Create the execution role with appropriate permissions (attach AWSLambdaBasicExecutionRole for CloudWatch logs)
3. Write your handler function in a file like index.js or lambda_function.py with the correct function signature for your runtime
4. Create a deployment.zip file containing only your handler code: zip deployment.zip index.js (do not include node_modules or venv)
5. Use aws lambda create-function with --handler, --role, --runtime, and --zip-file parameters
6. Test the function locally with aws lambda invoke --function-name <name> --payload '{}' response.json
7. View logs in CloudWatch with aws logs tail /aws/lambda/<function-name> --follow
8. Update the function code with aws lambda update-function-code --function-name <name> --zip-file fileb://deployment.zip after changes

Code

// index.js - Lambda handler for Node.js 18.x
exports.handler = async (event, context) => {
  console.log('Event received:', JSON.stringify(event, null, 2));
  
  try {
    // Extract data from event
    const body = event.body ? JSON.parse(event.body) : event;
    const name = body.name || 'World';
    
    // Process the request
    const message = `Hello, ${name}!`;
    
    // Return response in API Gateway format
    return {
      statusCode: 200,
      headers: {
        'Content-Type': 'application/json'
      },
      body: JSON.stringify({
        message: message,
        timestamp: new Date().toISOString(),
        requestId: context.requestId
      })
    };
  } catch (error) {
    console.error('Error processing request:', error);
    return {
      statusCode: 500,
      headers: {
        'Content-Type': 'application/json'
      },
      body: JSON.stringify({
        error: 'Internal server error',
        message: error.message
      })
    };
  }
};

// AWS CLI deployment script (deploy.sh)
#!/bin/bash

Note: this example was truncated in the source. See the GitHub repo for the latest full version.

Common Pitfalls

• Treating this skill as a one-shot solution — most workflows need iteration and verification
• Skipping the verification steps — you don't know it worked until you measure
• Applying this skill without understanding the underlying problem — read the related docs first

When NOT to Use This Skill

• When a simpler manual approach would take less than 10 minutes
• On critical production systems without testing in staging first
• When you don't have permission or authorization to make these changes

How to Verify It Worked

• Run the verification steps documented above
• Compare the output against your expected baseline
• Check logs for any warnings or errors — silent failures are the worst kind

Production Considerations

• Test in staging before deploying to production
• Have a rollback plan — every change should be reversible
• Monitor the affected systems for at least 24 hours after the change