Building APIs with Amazon API Gateway

Deploying Applications on AWS

Dunieski Otano

Amazon Web Services Solutions Architect

Three clients, one backend

Web, mobile, and a partner all call one backend
Each speaks a slightly different format
A front door validates and transforms every caller

Three client types connecting through a single API Gateway that routes requests to backend services

What API Gateway does

API Gateway as a managed front door: web and mobile clients route through a central gateway with routing, auth, throttling, and transformation features to Lambda, HTTP endpoints, and AWS services

A fully managed front door for your APIs
Handles routing, auth, throttling, and transformation
Sits between clients and your backend
Backends: Lambda, HTTP endpoints, or AWS services

Integration types

Lambda proxy: passes the whole request to Lambda
Lambda non-proxy: you map request and response fields
HTTP: forwards to an HTTP backend
MOCK: returns a response with no backend at all

Four API Gateway integration types: Lambda proxy passing full request, Lambda non-proxy using mapping templates, HTTP forwarding to an endpoint, and MOCK returning a static response

Request and response transformations

Mapping templates reshape payloads with VTL
Velocity Template Language transforms body, headers, params
Request mapping: client format to backend format
Response mapping: backend format to client format

VTL mapping template flow: client payload transformed by request template before reaching the backend, then backend response transformed by response template before returning to the client

Request validation

Request validation modes: validate body against JSON schema, validate required query and header parameters, or validate both before the Lambda backend is invoked

Reject bad input before it reaches the backend
Required parameters: headers, query strings, paths
Model schemas: validate the JSON body shape
Validate body, parameters, or both

Status codes and error contracts

Override backend status codes for a consistent contract
Map a backend 502 to a clean 503 for clients
Gateway responses: customize error bodies
Clients get predictable errors regardless of backend

Full API Gateway request lifecycle: validation rejects bad input at the gate, mapping template reshapes valid input for the backend, response template formats the output into a consistent client contract

Putting it together

Client request → validation → transformation → backend
Bad input rejected at the gate
Good input reshaped for the backend
Backend response reshaped into the client contract

Let's practice!

Deploying Applications on AWS