AWS Lambda Basics — Writing and Deploying Serverless Functions

# lambda_function.py
import json

def lambda_handler(event, context):
    """Lambda handler — entry point for every function"""
    print(f"Event: {json.dumps(event)}")

    name = event.get('name', 'World')

    return {
        'statusCode': 200,
        'headers': {'Content-Type': 'application/json'},
        'body': json.dumps({'message': f'Hello, {name}!'})
    }

# Create an IAM role (Lambda execution permissions)
aws iam create-role   --role-name lambda-basic-role   --assume-role-policy-document '{
    "Version": "2012-10-17",
    "Statement": [{
      "Effect": "Allow",
      "Principal": {"Service": "lambda.amazonaws.com"},
      "Action": "sts:AssumeRole"
    }]
  }'

# Attach the basic execution policy
aws iam attach-role-policy   --role-name lambda-basic-role   --policy-arn arn:aws:iam::aws:policy/service-role/AWSLambdaBasicExecutionRole

# Zip the code
zip function.zip lambda_function.py

# Create the function
aws lambda create-function   --function-name my-function   --runtime python3.12   --role arn:aws:iam::ACCOUNT_ID:role/lambda-basic-role   --handler lambda_function.lambda_handler   --zip-file fileb://function.zip   --timeout 30   --memory-size 256

# Invoke a test
aws lambda invoke   --function-name my-function   --payload '{"name": "Alice"}'   response.json
cat response.json

# Update the code
zip function.zip lambda_function.py
aws lambda update-function-code   --function-name my-function   --zip-file fileb://function.zip

aws lambda update-function-configuration   --function-name my-function   --environment 'Variables={DB_HOST=localhost,DB_NAME=mydb,ENV=production}'

# Use inside the function
import os
db_host = os.environ['DB_HOST']

# Create an HTTP API (v2, simpler and cheaper)
aws apigatewayv2 create-api   --name my-api   --protocol-type HTTP   --target arn:aws:lambda:ap-northeast-2:ACCOUNT:function:my-function

# Grant API Gateway permission to invoke Lambda
aws lambda add-permission   --function-name my-function   --statement-id api-gateway-invoke   --action lambda:InvokeFunction   --principal apigateway.amazonaws.com

# Get the API endpoint
aws apigatewayv2 get-apis --query 'Items[0].ApiEndpoint'

# Create a rule (every day at 09:00 UTC)
aws events put-rule   --name daily-job   --schedule-expression "cron(0 9 * * ? *)"   --state ENABLED

# Set Lambda as the target
aws events put-targets   --rule daily-job   --targets '[{
    "Id": "lambda-target",
    "Arn": "arn:aws:lambda:ap-northeast-2:ACCOUNT:function:my-function"
  }]'

# Grant EventBridge permission to invoke Lambda
aws lambda add-permission   --function-name my-function   --statement-id eventbridge-invoke   --action lambda:InvokeFunction   --principal events.amazonaws.com   --source-arn arn:aws:events:ap-northeast-2:ACCOUNT:rule/daily-job

# Configure S3 bucket notifications
aws s3api put-bucket-notification-configuration   --bucket my-bucket   --notification-configuration '{
    "LambdaFunctionConfigurations": [{
      "LambdaFunctionArn": "arn:aws:lambda:ap-northeast-2:ACCOUNT:function:my-function",
      "Events": ["s3:ObjectCreated:*"],
      "Filter": {
        "Key": {"FilterRules": [{"Name": "suffix", "Value": ".jpg"}]}
      }
    }]
  }'

# Tail recent logs
aws logs tail /aws/lambda/my-function --follow

# Specific time range
aws logs filter-log-events   --log-group-name /aws/lambda/my-function   --start-time $(date -d '1 hour ago' +%s000)