name: aws-development
description: AWS development best practices for Lambda, SAM, CDK, DynamoDB, IAM, and serverless architecture using Infrastructure as Code.

AWS Development Best Practices

Overview

This skill provides comprehensive guidelines for developing applications on Amazon Web Services (AWS), focusing on serverless architecture, Infrastructure as Code, and security best practices.

Core Principles

• Write clean, well-structured code with accurate AWS SDK examples
• Use Infrastructure as Code (Terraform, CDK, SAM) for all infrastructure
• Follow the principle of least privilege for all IAM policies
• Implement comprehensive logging, metrics, and tracing for observability

AWS Lambda Guidelines

Configuration Standards

• Use TypeScript implementation on ARM64 architecture for better performance and cost
• Set appropriate memory and timeout values based on workload requirements
• Use environment variables for configuration, never hardcode values
• Implement proper error handling and retry logic

Lambda Best Practices

// Use ES modules and typed handlers
import { APIGatewayProxyHandler } from 'aws-lambda';

export const handler: APIGatewayProxyHandler = async (event) => {
  try {
    // Validate input at function start
    if (!event.body) {
      return { statusCode: 400, body: JSON.stringify({ error: 'Missing body' }) };
    }

    // Business logic here

    return { statusCode: 200, body: JSON.stringify({ success: true }) };
  } catch (error) {
    console.error('Lambda error:', error);
    return { statusCode: 500, body: JSON.stringify({ error: 'Internal error' }) };
  }
};

AWS CDK Guidelines

Implementation Standards

• Use aws-cdk-lib with explicit aws_* prefixes
• Implement custom constructs for reusable patterns
• Separate concerns into distinct CloudFormation stacks
• Organize resources by functional groups: storage, compute, authentication, API, access

Project Structure

aws/
├── constructs/     # CDK custom constructs
├── stacks/         # CloudFormation stack definitions
├── functions/      # Lambda function implementations
└── tests/          # Infrastructure tests

CDK Best Practices

import * as cdk from 'aws-cdk-lib';
import * as lambda from 'aws-cdk-lib/aws_lambda';
import * as dynamodb from 'aws-cdk-lib/aws_dynamodb';

// Use custom constructs for reusable patterns
export class ApiConstruct extends Construct {
  constructor(scope: Construct, id: string, props: ApiProps) {
    super(scope, id);
    // Implementation
  }
}

DynamoDB Patterns

Table Design

• Design tables around access patterns, not entity relationships
• Use single-table design when appropriate
• Implement GSIs for additional access patterns
• Use on-demand capacity for variable workloads, provisioned for predictable

Best Practices

• Always use strongly typed item definitions
• Implement optimistic locking with version attributes
• Use batch operations for multiple items
• Enable point-in-time recovery for production tables

IAM Security Best Practices

Principles

• Apply least privilege: grant only permissions needed
• Use IAM roles, not access keys, for AWS service access
• Implement resource-based policies where appropriate
• Regular audit and rotate credentials

Policy Example

{
  "Version": "2012-10-17",
  "Statement": [
    {
      "Effect": "Allow",
      "Action": [
        "dynamodb:GetItem",
        "dynamodb:PutItem",
        "dynamodb:Query"
      ],
      "Resource": "arn:aws:dynamodb:*:*:table/MyTable"
    }
  ]
}

SAM Template Configuration

Template Structure

AWSTemplateFormatVersion: '2010-09-09'
Transform: AWS::Serverless-2016-10-31

Globals:
  Function:
    Timeout: 30
    Runtime: nodejs20.x
    Architectures:
      - arm64
    Tracing: Active

Resources:
  MyFunction:
    Type: AWS::Serverless::Function
    Properties:
      CodeUri: src/
      Handler: index.handler
      Events:
        Api:
          Type: Api
          Properties:
            Path: /items
            Method: GET

API Gateway Configuration

Best Practices

• Use Cognito or IAM for authentication
• Implement request validation
• Enable CORS only when necessary
• Use usage plans and API keys for rate limiting

Step Functions for Orchestration

• Use Step Functions for complex workflows
• Implement error handling with Catch and Retry
• Use Express workflows for high-volume, short-duration
• Use Standard workflows for long-running processes

Security Standards

Encryption

• Enable encryption at rest for all storage services
• Use AWS KMS for key management
• Enable encryption in transit (TLS)
• Use custom KMS keys for sensitive data

Secrets Management

• Store secrets in AWS Secrets Manager or Parameter Store
• Never commit secrets to version control
• Rotate secrets automatically
• Use IAM roles to access secrets

Observability

Logging

• Use structured JSON logging
• Include correlation IDs across services
• Log at appropriate levels (INFO, WARN, ERROR)
• Enable CloudWatch Logs Insights for querying

Monitoring

• Create CloudWatch alarms for critical metrics
• Use X-Ray for distributed tracing
• Implement custom metrics for business KPIs
• Set up dashboards for operational visibility

Testing

Unit Testing

• Mock AWS SDK calls in unit tests
• Use localstack or SAM local for integration testing
• Test IAM policies with policy simulator
• Validate CloudFormation/CDK with cfn-lint

Integration Testing

import { DynamoDBClient } from '@aws-sdk/client-dynamodb';
import { mockClient } from 'aws-sdk-client-mock';

const ddbMock = mockClient(DynamoDBClient);

beforeEach(() => {
  ddbMock.reset();
});

test('handler returns items', async () => {
  ddbMock.on(QueryCommand).resolves({ Items: [] });
  const result = await handler(event);
  expect(result.statusCode).toBe(200);
});

CI/CD Integration

• Use AWS CodePipeline or GitHub Actions for CI/CD
• Run cdk diff or sam validate before deployment
• Implement staging environments (dev, staging, prod)
• Use parameter overrides for environment-specific config

Common Pitfalls to Avoid

1. Hardcoding AWS credentials or secrets
2. Not setting appropriate Lambda timeouts
3. Ignoring cold start optimization
4. Over-provisioning resources
5. Not implementing proper error handling
6. Missing CloudWatch alarms
7. Inadequate IAM policies (too permissive)
8. Not using VPC when required for compliance