Módulo 5: Lambda + API Gateway

Tiempo estimado

30 minutos

5.1 Crear función Lambda

Archivo a crear

lambda/healthcheck.py

mkdir -p lambda

# lambda/healthcheck.py
import json
from datetime import datetime

def handler(event, context):
    return {
        "statusCode": 200,
        "headers": {
            "Content-Type": "application/json"
        },
        "body": json.dumps({
            "status": "healthy",
            "timestamp": datetime.now().isoformat(),
            "service": "arka-api"
        })
    }

5.2 Empaquetar Lambda

cd lambda
zip healthcheck.zip healthcheck.py
cd ..

5.3 CloudFormation para Lambda + API Gateway

Archivo a crear

cloudformation/lambda-api.yaml

AWSTemplateFormatVersion: '2010-09-09'
Description: 'Lambda + API Gateway para healthcheck'

Resources:
  # Rol IAM para Lambda
  LambdaExecutionRole:
    Type: AWS::IAM::Role
    Properties:
      RoleName: lambda-execution-role
      AssumeRolePolicyDocument:
        Version: '2012-10-17'
        Statement:
          - Effect: Allow
            Principal:
              Service: lambda.amazonaws.com
            Action: sts:AssumeRole
      ManagedPolicyArns:
        - arn:aws:iam::aws:policy/service-role/AWSLambdaBasicExecutionRole

  # Función Lambda
  HealthcheckFunction:
    Type: AWS::Lambda::Function
    Properties:
      FunctionName: healthcheck
      Runtime: python3.11
      Handler: healthcheck.handler
      Role: !GetAtt LambdaExecutionRole.Arn
      Code: 
        S3Bucket: "lambda-code-dev"
        S3Key: "lambda-healthcheck.zip"
      Timeout: 30
      MemorySize: 128

  # API Gateway REST API
  ArkaApi:
    Type: AWS::ApiGateway::RestApi
    Properties:
      Name: Arka API
      Description: API para servicios Arka

  # Resource /health
  HealthResource:
    Type: AWS::ApiGateway::Resource
    Properties:
      RestApiId: !Ref ArkaApi
      ParentId: !GetAtt ArkaApi.RootResourceId
      PathPart: health

  # Método GET
  HealthGetMethod:
    Type: AWS::ApiGateway::Method
    Properties:
      RestApiId: !Ref ArkaApi
      ResourceId: !Ref HealthResource
      HttpMethod: GET
      AuthorizationType: NONE
      Integration:
        Type: AWS_PROXY
        IntegrationHttpMethod: POST
        Uri: !Sub 
          - arn:aws:apigateway:${AWS::Region}:lambda:path/2015-03-31/functions/${LambdaArn}/invocations
          - LambdaArn: !GetAtt HealthcheckFunction.Arn

  # Permiso para que API Gateway invoque Lambda
  LambdaPermission:
    Type: AWS::Lambda::Permission
    Properties:
      FunctionName: !Ref HealthcheckFunction
      Action: lambda:InvokeFunction
      Principal: apigateway.amazonaws.com
      SourceArn: !Sub arn:aws:execute-api:${AWS::Region}:${AWS::AccountId}:${ArkaApi}/*

  # Deployment
  ApiDeployment:
    Type: AWS::ApiGateway::Deployment
    DependsOn: HealthGetMethod
    Properties:
      RestApiId: !Ref ArkaApi

  # Stage dev
  DevStage:
    Type: AWS::ApiGateway::Stage
    Properties:
      RestApiId: !Ref ArkaApi
      DeploymentId: !Ref ApiDeployment
      StageName: dev

Outputs:
  LambdaFunctionArn:
    Value: !GetAtt HealthcheckFunction.Arn
  ApiGatewayUrl:
    Value: !Sub https://${ArkaApi}.execute-api.${AWS::Region}.amazonaws.com/dev/health
  LocalStackUrl:
    Value: !Sub http://localhost:4566/restapis/${ArkaApi}/dev/_user_request_/health

5.4 Desplegar stack

awslocal cloudformation deploy \
  --stack-name lambda-api-stack \
  --template-file cloudformation/lambda-api.yaml \
  --capabilities CAPABILITY_NAMED_IAM

5.5 Obtener URL y probar

# Obtener API ID
API_ID=$(awslocal apigateway get-rest-apis \
  --query 'items[?name==`Arka API`].id' --output text)

echo "API URL: http://localhost:4566/restapis/$API_ID/dev/_user_request_/health"

# Probar endpoint
curl http://localhost:4566/restapis/$API_ID/dev/_user_request_/health | jq

Checkpoint

El endpoint debe retornar {"status": "healthy", ...}

Arquitectura Lambda + API Gateway

Conceptos Clave

Componente	Propósito
Lambda Function	Código que se ejecuta sin servidor
API Gateway	Proxy HTTP para exponer APIs
Stage	Ambiente de despliegue (dev, prod)
Integration	Conexión entre API Gateway y Lambda

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Siguiente: Módulo 6: Stack Completo