AWS Serverless

Mental model

AWS Serverless is an architectural paradigm where cloud infrastructure management is fully offloaded to AWS. Applications are decomposed into event-driven, stateless components that execute on demand, auto-scale from zero to peak demand, and bill strictly for consumed resources.

Core compute and routing

Component	Responsibility
AWS Lambda	Stateless execution triggered by events
API Gateway	REST & HTTP endpoints, routing, auth
Lambda Layers	Shared code libraries and binaries

AWS Lambda executes code in isolated environments. Warm starts reuse existing execution contexts, while cold starts initialize new instances. API Gateway maps incoming HTTP requests directly to Lambda event payloads and converts return objects into HTTP responses.

export async function handler(
  event: { body?: string }
) {
  const data = JSON.parse(
    event.body ?? "{}"
  );
  return {
    statusCode: 200,
    body: JSON.stringify({
      message: "Success",
      data,
    }),
  };
}

Gotcha: Global variables persist across invocations during warm starts. Never store request-specific state in global variables.

Data and storage

Datastore	Best for
DynamoDB	Key-value & document NoSQL datastore
Amazon S3	Scalable object storage for files/blobs
ElastiCache	In-memory caching for low latency

DynamoDB provides single-digit millisecond performance at scale. Single-table design uses composite primary keys (Partition Key + Sort Key) to store multiple entity types in one table, querying related data in a single request without costly joins.

type Item = { pk: string; sk: string };

function buildParams(item: Item) {
  return {
    TableName: "MainTable",
    Item: {
      PK: { S: item.pk },
      SK: { S: item.sk },
    },
  };
}

Warning: DynamoDB scans inspect the entire table and consume high capacity. Always prefer queries on primary keys or Secondary Indexes.

Event integration and messaging

Service	Delivery model
EventBridge	Event bus for decoupling services
SQS	Queueing for asynchronous processing
SNS	Pub/Sub topic for multi-receiver fanout

Serverless systems use asynchronous messaging to decouple producers and consumers. EventBridge filters and routes domain events across microservices. SQS queues handle backpressure and retry buffering, while SNS broadcasts messages to multiple subscribers simultaneously.

{
  "source": "app.orders",
  "detail-type": "OrderCreated",
  "detail": {
    "orderId": "ord-9921",
    "amount": 49.99
  }
}

Tip: Pair SQS FIFO queues with Lambda when strict FIFO ordering and message deduplication are required.

Orchestration and security

Tool	Purpose
Step Functions	State machine workflow orchestration
IAM Execution Role	Grants permissions to Lambda functions
Resource Policy	Controls access to API Gateway/SQS

AWS Step Functions coordinates multi-step workflows with built-in retries, branching logic, and error handling without custom orchestrator code. Security operates under the principle of least privilege using IAM execution roles assigned directly to compute resources.

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

Gotcha: Granting wildcard permissions (*) in IAM execution roles exposes the serverless resource to unauthorized escalation.

Deployment and IaC

Framework	Focus
AWS SAM	Open-source framework for serverless IaC
AWS CDK	Define cloud infrastructure in TS/Python
Serverless Framework	Multi-cloud serverless deployment

Infrastructure-as-Code (IaC) allows serverless stacks to be defined declaratively and versioned in source control. AWS SAM extends CloudFormation with concise syntax for functions, APIs, and databases. AWS CDK enables constructing serverless stacks using programming languages.

AWSTemplateFormatVersion: '2010-09-09'
Transform: AWS::Serverless-2016-10-31
Resources:
  GetOrderFunction:
    Type: AWS::Serverless::Function
    Properties:
      CodeUri: src/
      Handler: app.handler
      Runtime: nodejs22.x
      Events:
        Api:
          Type: Api
          Properties:
            Path: /orders/{id}
            Method: get

Tip: Use SAM local (sam local invoke) to test Lambda functions locally against simulated API Gateway events before deploying.

Further reading

• AWS Serverless Application Model (SAM) Guide
• AWS Lambda Developer Documentation
• Amazon DynamoDB Developer Guide
• Amazon EventBridge User Guide