Serverless AWS

Serverless AWS Skill

Patterns for AWS Lambda, DynamoDB, SQS, and Secrets Manager.

When to Use

Apply when working on serverless AWS projects using Lambda functions.

Lambda Handler Structure

export async function handle(event: AWSLambda.APIGatewayProxyEvent) {
    try {
        return await handleInternal(event);
    } catch (error) {
        await trace.error(error, { headers: event.headers, body: event.body });
        return createErrorResponse(error);
    }
}

async function handleInternal(event: AWSLambda.APIGatewayProxyEvent) {
    const isAuthenticated = await authenticateRequest(event);
    if (!isAuthenticated) return unauthorizedResponse();

    const body = JSON.parse(event.body);
    assert(isValidInput(body), 'Invalid request body');
    return processRequest(body);
}

Cold Start Optimization

Initialize clients outside handler:

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

const dynamoClient = new DynamoDBClient({ region: 'us-east-1' });

let configCache: Config;

export async function handle(event: any) {
    if (!configCache) configCache = await loadConfig();
    return process(event, configCache);
}

SQS Processing

export async function handle(event: SQSEvent) {
    assert(event.Records.length === 1, 'Expected single record');
    
    const record = event.Records[0];
    const message = JSON.parse(record.body);
    const type = record.messageAttributes?.type?.stringValue;

    switch (type) {
        case 'ORDER_UPDATE': return handleOrderUpdate(message);
        case 'CUSTOMER_SYNC': return handleCustomerSync(message);
        default: console.warn('Unknown message type', type);
    }
}

External API Calls

export async function callExternalAPI(endpoint: string, data: any) {
    const config = await getServiceConfig();
    
    try {
        const response = await fetch(`${config.base_url}${endpoint}`, {
            method: 'POST',
            headers: {
                'Authorization': `Bearer ${config.api_key}`,
                'Content-Type': 'application/json'
            },
            body: JSON.stringify(data)
        });
        
        if (!response.ok) {
            throw new StatusCodeError(response.status, await response.text());
        }
        
        return response.json();
    } catch (error) {
        await trace.error('External API call failed', { endpoint, error });
        throw error;
    }
}

Deduplication

const processedEvents = new Map<string, number>();

function isDuplicate(eventId: string): boolean {
    const now = Date.now();
    const fiveMinutesAgo = now - (5 * 60 * 1000);
    
    // Clean old entries
    for (const [id, timestamp] of processedEvents.entries()) {
        if (timestamp < fiveMinutesAgo) {
            processedEvents.delete(id);
        }
    }
    
    if (processedEvents.has(eventId)) return true;
    
    processedEvents.set(eventId, now);
    return false;
}