API Gateway

AWS API Gateway

Amazon API Gateway is a fully managed service for creating, publishing, and securing APIs at any scale. Supports REST APIs, HTTP APIs, and WebSocket APIs.

Table of Contents

• Core Concepts
• Common Patterns
• CLI Reference
• Best Practices
• Troubleshooting
• References

Core Concepts

API Types

Key Components

• Resources: URL paths (/users, /orders/{id})
• Methods: HTTP verbs (GET, POST, PUT, DELETE)
• Integrations: Backend connections (Lambda, HTTP, AWS services)
• Stages: Deployment environments (dev, prod)

Integration Types

Common Patterns

Create HTTP API with Lambda

AWS CLI:

# Create HTTP API
aws apigatewayv2 create-api \
  --name my-api \
  --protocol-type HTTP \
  --target arn:aws:lambda:us-east-1:123456789012:function:MyFunction

# Get API endpoint
aws apigatewayv2 get-api --api-id abc123 --query 'ApiEndpoint'

SAM Template:

AWSTemplateFormatVersion: '2010-09-09'
Transform: AWS::Serverless-2016-10-31

Resources:
  MyApi:
    Type: AWS::Serverless::HttpApi
    Properties:
      StageName: prod

  MyFunction:
    Type: AWS::Serverless::Function
    Properties:
      Handler: app.handler
      Runtime: python3.12
      Events:
        ApiEvent:
          Type: HttpApi
          Properties:
            ApiId: !Ref MyApi
            Path: /items
            Method: GET

Create REST API with Lambda Proxy

# Create REST API
aws apigateway create-rest-api \
  --name my-rest-api \
  --endpoint-configuration types=REGIONAL

API_ID=abc123

# Get root resource ID
ROOT_ID=$(aws apigateway get-resources --rest-api-id $API_ID --query 'items[0].id' --output text)

# Create resource
aws apigateway create-resource \
  --rest-api-id $API_ID \
  --parent-id $ROOT_ID \
  --path-part items

RESOURCE_ID=xyz789

# Create method
aws apigateway put-method \
  --rest-api-id $API_ID \
  --resource-id $RESOURCE_ID \
  --http-method GET \
  --authorization-type NONE

# Create Lambda integration
aws apigateway put-integration \
  --rest-api-id $API_ID \
  --resource-id $RESOURCE_ID \
  --http-method GET \
  --type AWS_PROXY \
  --integration-http-method POST \
  --uri arn:aws:apigateway:us-east-1:lambda:path/2015-03-31/functions/arn:aws:lambda:us-east-1:123456789012:function:MyFunction/invocations

# Deploy to stage
aws apigateway create-deployment \
  --rest-api-id $API_ID \
  --stage-name prod

Lambda Handler for API Gateway

import json

def handler(event, context):
    # HTTP API event
    http_method = event.get('requestContext', {}).get('http', {}).get('method')
    path = event.get('rawPath', '')
    query_params = event.get('queryStringParameters', {})
    body = event.get('body', '')

    if body and event.get('isBase64Encoded'):
        import base64
        body = base64.b64decode(body).decode('utf-8')

    # Process request
    response_body = {'message': 'Success', 'path': path}

    return {
        'statusCode': 200,
        'headers': {
            'Content-Type': 'application/json'
        },
        'body': json.dumps(response_body)
    }

Configure CORS

HTTP API:

aws apigatewayv2 update-api \
  --api-id abc123 \
  --cors-configuration '{
    "AllowOrigins": ["https://example.com"],
    "AllowMethods": ["GET", "POST", "PUT", "DELETE"],
    "AllowHeaders": ["Content-Type", "Authorization"],
    "MaxAge": 86400
  }'

REST API:

# Enable CORS on resource
aws apigateway put-method \
  --rest-api-id $API_ID \
  --resource-id $RESOURCE_ID \
  --http-method OPTIONS \
  --authorization-type NONE

aws apigateway put-integration \
  --rest-api-id $API_ID \
  --resource-id $RESOURCE_ID \
  --http-method OPTIONS \
  --type MOCK \
  --request-templates '{"application/json": "{\"statusCode\": 200}"}'

aws apigateway put-method-response \
  --rest-api-id $API_ID \
  --resource-id $RESOURCE_ID \
  --http-method OPTIONS \
  --status-code 200 \
  --response-parameters '{
    "method.response.header.Access-Control-Allow-Headers": true,
    "method.response.header.Access-Control-Allow-Methods": true,
    "method.response.header.Access-Control-Allow-Origin": true
  }'

aws apigateway put-integration-response \
  --rest-api-id $API_ID \
  --resource-id $RESOURCE_ID \
  --http-method OPTIONS \
  --status-code 200 \
  --response-parameters '{
    "method.response.header.Access-Control-Allow-Headers": "'''Content-Type,Authorization'''",
    "method.response.header.Access-Control-Allow-Methods": "'''GET,POST,PUT,DELETE,OPTIONS'''",
    "method.response.header.Access-Control-Allow-Origin": "'''*'''"
  }'

JWT Authorization (HTTP API)

aws apigatewayv2 create-authorizer \
  --api-id abc123 \
  --name jwt-authorizer \
  --authorizer-type JWT \
  --identity-source '$request.header.Authorization' \
  --jwt-configuration '{
    "Issuer": "https://cognito-idp.us-east-1.amazonaws.com/us-east-1_abc123",
    "Audience": ["client-id"]
  }'

CLI Reference

HTTP API (apigatewayv2)

REST API (apigateway)

Best Practices

Performance

• Use HTTP APIs for simple use cases (70% cheaper, lower latency)
• Enable caching for REST APIs
• Use regional endpoints unless global distribution needed
• Implement pagination for list endpoints

Security

• Use authorization on all endpoints
• Enable WAF for REST APIs
• Use API keys for rate limiting (not authentication)
• Enable access logging
• Use HTTPS only

Reliability

• Set up throttling to protect backends
• Configure timeout appropriately
• Use canary deployments for updates
• Monitor with CloudWatch

Troubleshooting

403 Forbidden

Causes:

• Missing authorization
• Invalid API key
• WAF blocking
• Resource policy denying

Debug:

# Check API key
aws apigateway get-api-key --api-key abc123 --include-value

# Check authorizer
aws apigatewayv2 get-authorizer --api-id abc123 --authorizer-id xyz789

502 Bad Gateway

Causes:

• Lambda error
• Integration timeout
• Invalid response format

Lambda response format:

# Correct format
return {
    'statusCode': 200,
    'headers': {'Content-Type': 'application/json'},
    'body': json.dumps({'message': 'success'})
}

# Wrong - missing statusCode
return {'message': 'success'}

504 Gateway Timeout

Causes:

• Backend timeout (Lambda max 29 seconds for REST API)
• Integration timeout too short

Solutions:

• Increase Lambda timeout
• Use async processing for long operations
• Increase integration timeout (max 29s for REST, 30s for HTTP)

CORS Errors

Debug:

• Check OPTIONS method exists
• Verify headers in response
• Check origin matches allowed origins

References

• API Gateway Developer Guide
• API Gateway REST API Reference
• API Gateway CLI Reference
• boto3 API Gateway

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