Backend6 min read

Serverless Architecture

Build event-driven serverless applications - Lambda functions, API Gateway, cold starts, IAM, and the Serverless Framework for infrastructure-as-code.

ServerlessAWS LambdaFaaSCloud FunctionsEvent-Driven

skill: Serverless Architecture category: Backend tags: [Serverless, AWS Lambda, FaaS, Cloud Functions, Event-Driven] readingTime: 6

Serverless eliminates server management - you pay per invocation, scale automatically, and deploy code without provisioning. Use it for event-driven tasks, APIs with variable traffic, and batch processing. Avoid it for long-running processes (> 15 min), warm connection pools (DB connections), or very high-throughput sustained loads where EC2 is cheaper.

Workflow

Write Lambda functions correctlyLambda runs a handler function - the runtime reuses the execution environment between invocations, enabling connection reuse but requiring careful global state management.
Deploy with the Serverless FrameworkThe Serverless Framework translates a simple YAML config into the full CloudFormation stack - Lambda, API Gateway, IAM roles, event sources.
Optimize cold startsCold starts (first invocation after idle period) add 100ms-2s latency. For user-facing APIs, this degrades perceived performance.
Handle concurrent invocations and throttlingLambda has per-account and per-function concurrency limits. Without reserved concurrency, one function can starve others.
Connect databases efficientlyLambda creates new DB connections per cold start - 1000 concurrent Lambdas = 1000 connections, exceeding PostgreSQL limits.

Output Format

Serverless: Lambda handler with reused connections, Serverless Framework YAML, provisioned concurrency, reserved concurrency, and RDS Proxy.

serverless.yml:
  provider: { runtime, iam.role.statements }
  functions: { handler, events: [httpApi], timeout, memorySize }
  resources: { DynamoDB, SQS, etc. }

Examples

Input

Output

Edge Cases & Gotchas

Lambda execution time limit - Maximum Lambda timeout is 15 minutes. For longer processes, use Step Functions, ECS tasks, or Batch - not Lambda.
Payload size limits - API Gateway request/response payloads are limited to 10MB. For large uploads, use presigned S3 URLs - Lambda should never receive binary files directly.
Environment variable encryption - Lambda environment variables are encrypted at rest but visible in the AWS console. Use SSM Parameter Store or Secrets Manager for secrets that shouldn't be visible in plaintext.
VPC cold starts - Lambda in a VPC used to have 10+ second cold starts for ENI attachment. AWS resolved this in 2020 - VPC cold starts are now <1s in most regions.

When to Break These Rules

Use ECS Fargate or containers for tasks that need > 15 min runtime, shared filesystem, or stable warm connections.
Use serverless sparingly when your traffic is consistently high - EC2 or ECS is cheaper at sustained 1000+ RPS.

Reference Files

https://docs.aws.amazon.com/lambda/
https://www.serverless.com/framework/docs