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api-gateway.md

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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 Architecture

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