Serverless

Serverless

Serverless is a cloud-native development model for building and running applications without managing servers. The cloud provider handles the routine work of provisioning, maintaining, and scaling the server infrastructure.

When to Use

• Event-driven background tasks (Image processing, Cron jobs).
• APIs with spiky or unpredictable traffic (Auto-scales instantly).
• Startup/MVP where "Scale to Zero" (Zero cost when idle) is critical.
• Glue code between cloud services (e.g., S3 trigger -> Lambda -> DynamoDB).

Quick Start

// AWS Lambda Handler (Node.js)
export const handler = async (event) => {
  console.log("Event received:", JSON.stringify(event));

  const name = event.queryStringParameters?.name || "World";

  return {
    statusCode: 200,
    body: JSON.stringify({ message: `Hello, ${name}!` }),
  };
};

# serverless.yml (Serverless Framework)
service: my-api
provider:
  name: aws
  runtime: nodejs20.x

functions:
  hello:
    handler: handler.hello
    events:
      - httpApi:
          path: /hello
          method: get

Core Concepts

FaaS (Function as a Service)

Upload code (Function), define triggers (HTTP, Queue, DB, Timer). Run only when triggered.

Cold Start

The latency incurred when a function is invoked after being idle (container spinning up).

Statelessness

Functions are ephemeral. Store state in external managed services (Redis, DynamoDB, S3).

Common Patterns

Fan-out

One event triggers multiple parallel functions (e.g., Upload -> [Resize, Analyze, Back up]).

Strangler Fig

Migrating a monolith by gradually replacing endpoints with serverless functions routed via API Gateway.

Best Practices

Do:

• Use Frameworks (SST, Serverless Framework, SAM) for IaC.
• optimize Cold Starts (keep functions small, use provisioned concurrency if needed).
• Use Managed Services (DynamoDB, EventBridge) instead of custom code logic.

Don't:

• Don't use Serverless for Long-Running tasks (Gateways timeout at ~30s, Lambdas at 15m). Use Fargate/Batch for that.
• Don't ignore vendor lock-in (though often the speed creates enough value to justify it).

Troubleshooting

Error	Cause	Solution
Timeout	Function took too long.	Increase timeout setting; optimize code; move to async pattern.
OOM (Out of Memory)	Processing large files.	Increase RAM (allocates more CPU too); stream data instead of loading all in memory.

References

• Serverless Land (AWS)
• SST (Serverless Stack)