aws-lambda

aws-lambda Best Practices

This guide outlines the definitive best practices for developing AWS Lambda functions. Adhere to these principles to build reliable, cost-effective, and secure serverless applications.

Code Organization and Structure

1. Single Responsibility Principle: Each Lambda function must perform one distinct task. Decompose complex workflows into smaller, focused functions orchestrated by services like AWS Step Functions.

2. Initialize Outside the Handler: Leverage execution environment reuse by initializing SDK clients, database connections, and heavy dependencies in the global scope.

❌ BAD:

import boto3

def handler(event, context):
    s3 = boto3.client('s3') # Initialized on every invocation
    # ...

✅ GOOD:

import boto3

s3 = boto3.client('s3') # Initialized once per execution environment

def handler(event, context):
    # s3 client is reused across invocations
    # ...

3. Use Lambda Layers for Shared Code: Keep deployment packages small and promote code reuse for common libraries and dependencies.

4. Configuration via Environment Variables: Never hardcode operational parameters. Use environment variables for dynamic configuration. For sensitive data, use AWS Secrets Manager or AWS Systems Manager Parameter Store.

5. Structured JSON Logging: Output logs in JSON format to CloudWatch. This makes logs easily queryable and analyzable. Use aws-lambda-powertools Logger utility.

❌ BAD:

print(f"Processing event: {event}")

✅ GOOD:

from aws_lambda_powertools import Logger
logger = Logger()

@logger.inject_lambda_context
def handler(event, context):
    logger.info("Processing event", event=event)
    # ...

6. Infrastructure as Code (AWS CDK v2): Define your Lambda functions and their surrounding infrastructure (API Gateway, DynamoDB, IAM roles) using AWS CDK v2. This ensures version control, repeatability, and safe deployments.

✅ GOOD:

# Example using AWS CDK v2 (Python)
from aws_cdk import Stack, aws_lambda as lambda_
from constructs import Construct

class MyLambdaStack(Stack):
    def __init__(self, scope: Construct, construct_id: str, **kwargs) -> None:
        super().__init__(scope, construct_id, **kwargs)

        lambda_.Function(self, "MyHandler",
            runtime=lambda_.Runtime.PYTHON_3_12,
            handler="index.handler",
            code=lambda_.Code.from_asset("lambda"), # 'lambda' directory contains index.py
            environment={
                "TABLE_NAME": "MyTable",
            },
            # Add more configurations like memory, timeout, IAM roles
        )