API Gateway

• Is a service which lets us create and manage APIs
• API Gateway acts as endpoint or entry-point applications which want to talk with our services
• Sits between the application and integrations (services)
• API Gateway is HA and scalable
• Handles authorization, throttling, caching, CORS, transformations
• It also supports the OpenAPI spec and direct integration with other AWS services
• API gateway is a public service
• It can provide APIs using REST and WebSocket
• API Gateway overview:

API Gateway - Authentication

• API Gateway supports a range of authentication types, example Cognito, Lambda based authentication (Custom based authentication - Bearer token), IAM credentials, etc.

API Gateway - Endpoint Types

• Edge-Optimized: any incoming request is routed to the nearest CloudFront POP (point of presence)
• Region: region endpoint for clients in the same region
• Private: endpoints only accessible in a VPC via interface endpoints

API Gateway - Stages

• When we deploy an API configuration, we are doing it into a stage
• Example we can have prod/dev stage with uniq settings and urls
• Deployments can be rolled back on a stage
• On stages we can enable canary deployments. When enabled, the deployment will be made to the canary not the stage itself
• Traffic distribution can be altered between canary and base stage
• Canary stage can be promoted to base

API Gateway - Errors

• 4XX - Client errors: invalid request on the client side
• 5XX - Server errors: valid request, backend issue
• 400 - Bad Request: generic client side error
• 403 - Access Denied: authorizer denies request, request is WAF filtered
• 429 - API Gateway can throttle: this means we have exceeded a specified amount of requests
• 502 - Bad Gateway Exception: bad output returned by Lambda
• 503 - Service Unavailable: backing endpoint is offline
• 504 - Integration Failure/Timeout (29s limit)

API Gateway - Caching

• Caching is configured per stage
• We can define a cache on a stage (500 MB up to 237 GB)
• Cache TTL default value is 300 seconds, configurable between 0 and 3600s. Can be encrypted
• Calls only will reach the backend in case of a cache miss

API Gateway Methods and Resources

• API Gateway URL example: https://1nj7i16t37.execute-api.us-east-1.amazonaws.com/dev/listcats
• The URL can be represents the following: [api-gateway-endpoint]/[stage]/[resource]
• Stages are logical configurations. APIs are deployed into stages. Stages can be used for different application versions or lifecycle points for an API
• API changes only take effect after it is deployed into a stage
• Methods are the desired action to be performed. Methods are HTTP verbs
• Methods are where integrations are configured which provide the functionality of an API. Methods can integrate with Lambda, HTTP and other AWS services

API Gateway Integrations

• API Gateway is capable of connecting to Lambda, HTTP Endpoints (running on-premises or on AWS), Step Functions, SNS, DynamoDB
• APIs have 3 phases:
  • Request: authorize, validate and transform the request
  • Integrations
  • Response: transform, prepare and return the response
• The request and response phases are split into 2 parts:
  • Method Request: defines everything about the client request to method
  • Integration Request: parameters from the method request are transferred to the integrations
  • Integration Response: converts the data from the backend to a form which can be sent back to the client
  • Method Response: how the communication is delivered back to the client
• API methods which are on the client side decide what the client request to method is like. There are integrated to a backend endpoint via integrations
• Integration types:
  • Mock: used for testing, no backed involved. No real backend needed
  • HTTP: http custom integration. We have to configure both integration request and integration response
  • HTTP Proxy: subtype of HTTP where. Allows the access HTTP endpoint with a streamline integration. Proxying is where the request is passed to the endpoint as is and sent back to the client as is
  • AWS: allows an API to expose AWS services. We have to configure both the integration request and response
  • AWS_PROXY (LAMBDA): integration request/response does not have to be defined, API Gateway passes the request unmodified
• Mapping template: used for non-proxy integrations. Used for:
  • Modify or rename parameters
  • Modify the body or header of the request
  • Filtering - remove anything from the request
• Mapping uses VTL (Velocity Template Langue) for editing the request

API Gateway Stages and Deployments

• Editing an API, we are editing settings which are not live (not published)
• The current state of the API needs to be deployed to a stage
• Each stage has its own configuration. Configurations are not immutable, can be modified, overwritten or rolled back
• Stage variables: environment variables for stages

Swagger and OpenAPI

• OpenAPI (OAS) defines a standard language-agnostic interface to RESTful APIs
• OpenAPI v2 is formerly known as Swagger
• OpenAPI v3 is a more recent version
• OpenAPI defines endpoints, operation (GET, POST, etc.), input and output parameters and authentication methods
• API Gateway is capable of import OpenAPI format and generating it. Useful for backups and migrations