Spring API Gateway

👉 Learn Spring Cloud concepts.

8. API Gateway

Project ref: b7-api-gateway

Purpose / Feature
- All requests will be routed via API Gateway.
- This gives us flexibility to implement all common features at one place.
- Build on top of Spring WebFlux (Reactive Approach).
- Provide cross cutting concerns
  - Security
  - Monitoring / Metrics
- Features:
  - Match routes to any request attribute to route to right service.
  - Allows to define Predicates (Matcher) & Filters (eg. Authentication, Authorization, Logging etc.).
  - Integrates with Spring Cloud Discovery client to load balancing to the service for which the request is received.
  - Path rewriting.
Steps
- Step-1: Ensure following dependencies are added.
  - Eureka Discovery Client
  - Reactive API Gateay
- Step-2: Enable API gateway client discovery in application.properties
- Step-3: Now, we can access services with the Service name registered in Eureka server and path to controller API.
  - http://localhost:8765/B5-CURRENCY-CONVERSION-SERVICE-OPENFEIGN/currency-conversion-feign/from/UsD/to/iNr/quantity/100
- Step-4: Add property to accept service name in lower case
  - http://localhost:8765/b5-currency-conversion-service-openfeign/currency-conversion-feign/from/UsD/to/iNr/quantity/100
Maven / External dependency
- Required dependency. ```xml org.springframework.cloudspring-cloud-starter-gatewayorg.springframework.cloudspring-cloud-starter-netflix-eureka-client

Code / Config changes

Application Config:application.properties

    spring.application.name=b7-api-gateway
    server.port=8765

    # Start: Eureka client config

    # Map of availability zone to list of fully qualified URLs to communicate with eureka server. 
    # Each value can be a single URL or a comma separated list of alternative locations. 
    # Typically the eureka server URLs carry protocol,host,port,context and version information if any. 
    # Example: https://ec2-256-156-243-129.compute-1.amazonaws.com:7001/eureka/ 
    eureka.client.service-url.defaultZone=http://localhost:8761/eureka

    # Enables the Eureka health check handler.
    eureka.client.healthcheck.enabled=true

    eureka.instance.lease-renewal-interval-in-seconds=60
    eureka.instance.lease-expiration-duration-in-seconds=60

    # End: Eureka client config

    # Start: Api Gateway

    # Flag that enables Discovery Client gateway integration.
    # This allows us to invoke service using service-name registered in Eureka
    # http://localhost:8765/B3-CURRENCY-EXCHANGE-SERVICE/currency-exchange/from/usd/to/inr
    spring.cloud.gateway.discovery.locator.enabled=true

    # Option to lower case serviceId in predicates and filters, defaults to false. 
    # Useful with eureka when it automatically uppercases serviceId. so MYSERIVCE, would match /myservice/**
    spring.cloud.gateway.discovery.locator.lower-case-service-id=true

    # End: Api Gateway

Note: This is an important note.

Notes:
- Service client discovery is disabled by default. It need to be enabed explicitly in application.properties. Check above config for details.
References:
- https://docs.spring.io/spring-cloud-gateway/docs/current/reference/html/

9. Routes with spring cloud gateway

Project ref: b8-api-gateway-routes

Purpose / Feature
- API Gateway Routers and Filters provides the option to intercept and process the requests.
- It provides methods/APIs to match request on any attribute - method, header, cookie, path, host etc..
- It allow to route specific URLs to desired service.
- We can add HTTP headers & params in the request.
- We can also rewrite the URL.
- We can also implement common checks such as authentication, authorization, logging etc.
Steps
- Step-1: Considering tht API Gateway is already implemented.
  - If not, refer section 8 above for API Gateway coniguration.
- Step-2: Update application configuration in application.properties.
  - Disable gateway discovery locator configuration in application.properties to auto discover clients from Eureka server.
- Step-3: Create a Configuration class.
  - Create a Bean of o.s.c.gateway.route.RouteLocator class with method accepting RouteLocatorBuilder class as argument.
  - Now using RouteLocatorBuilder instance, we can customize routes, e.g.
    - Route any URL to lb://<service-name-in-eureka> to redirect and do load-balancing.
    - Route to any external service http://httpbin.org/.
      - Request failing for HTTPS requests, requires SSL confguration.
    - Rewrite the requested URL to corresponfing inernal service URL using filters.
Maven / External dependency
- Required dependency. ```xml org.springframework.cloudspring-cloud-starter-gatewayorg.springframework.cloudspring-cloud-starter-netflix-eureka-client

Code / Config changes

Configuratio:ApiGatewayConfiguration.java
- imports
  - import org.springframework.cloud.gateway.route.RouteLocator;
  - import org.springframework.cloud.gateway.route.builder.RouteLocatorBuilder;
  - import org.springframework.cloud.gateway.route.builder.RouteLocatorBuilder.Builder;
- Create a Bean of RouteLocator class. ```java /**
  - Configuration class to build custom routes and request customization. */ @Configuration public class ApiGatewayConfiguration {
    /**
    - Define routes.
    - @param routeLocatorBuilder
    - @return / @Bean RouteLocator getwayRoute(RouteLocatorBuilder routeLocatorBuilder) { /
      - Redirect request to external service. Also, optionally we can add http
      - headers and request params in the request. */ Builder routeLocator = routeLocatorBuilder.routes() .route((p) -> p.path(“/get”) .filters(f -> f.addRequestHeader(“MY-HEADER”, “MY-CUSTOM-HEADER”) .addRequestParameter(“MY-REQUEST-PARAM”, “MY-CUSTOM-REQUEST-PARAM”)) .uri(“http://httpbin.org:80/”));
      /**
      - Route URLs to load balancer and eureka service name */ routeLocator = routeLocator.route(p -> p.path(“/currency-exchange/”).uri(“lb://b3-currency-exchange-service”)) .route(p -> p.path(“/currency-conversion-feign/”) .uri(“lb://b5-currency-conversion-service-openfeign”));
      /**
      - Rewrite URL and copy the path */ routeLocator.route(p -> p.path(“/ccfs/**”) .filters(f -> f.rewritePath(“/ccfs/(?.*)", "/currency-conversion-feign/${segment}")) .uri("lb://b5-currency-conversion-service-openfeign"));
      return routeLocator.build(); } } ```

Application Config:application.properties

    spring.application.name=b8-api-gateway-routes

    server.port=8765

    # Start: Eureka client config

    # Map of availability zone to list of fully qualified URLs to communicate with eureka server. 
    # Each value can be a single URL or a comma separated list of alternative locations. 
    # Typically the eureka server URLs carry protocol,host,port,context and version information if any. 
    # Example: https://ec2-256-156-243-129.compute-1.amazonaws.com:7001/eureka/ 
    eureka.client.service-url.defaultZone=http://localhost:8761/eureka

    # Enables the Eureka health check handler.
    eureka.client.healthcheck.enabled=true

    eureka.instance.lease-renewal-interval-in-seconds=60
    eureka.instance.lease-expiration-duration-in-seconds=60

    # End: Eureka client config


    # Start: Api Gateway

    # Flag that enables Discovery Client gateway integration.
    # This allows us to invoke service using service-name registered in Eureka
    # http://localhost:8765/B3-CURRENCY-EXCHANGE-SERVICE/currency-exchange/from/usd/to/inr
    # Disbling - to use Routes and Filters
    #spring.cloud.gateway.discovery.locator.enabled=true
    spring.cloud.gateway.discovery.locator.enabled=false

    # Option to lower case serviceId in predicates and filters, defaults to false. 
    # Useful with eureka when it automatically uppercases serviceId. so MYSERIVCE, would match /myservice/**
    # Disbling - to use Routes and Filters
    #spring.cloud.gateway.discovery.locator.lower-case-service-id=true
    spring.cloud.gateway.discovery.locator.lower-case-service-id=false

    # Option to lower case serviceId in predicates and filters, defaults to false. 
    # Useful with eureka when it automatically uppercases serviceId. so MYSERIVCE, would match /myservice/**
    # spring.cloud.gateway.discovery.locator.lowerCaseServiceId=true

    # End: Api Gateway	

Note: When using routes in API Gateway, eureka discover client must be disabled in application.properties.

References:
- https://docs.spring.io/spring-cloud-gateway/reference/spring-cloud-gateway-server-mvc/filters/rewritepath.html

10. API Gateway : Global filter

Project ref: b8-api-gateway-routes

Purpose / Feature
- Contract for interception-style, chained processing of gateway requests that may be used to implement cross-cutting, application-agnostic requirements such as security, timeouts, and others
- Only applies to matched gateway routes. Copied from framework WebFilter.
Steps
- Step-1: Considering tht API Gateway is already implemented with working routes config
  - If not, refer section 8 & section 9 above for API Gateway coniguration.
- Step-2: Create a class implementing o.s.c.g.filter.GlobalFilter class.
- Step-3: Override filter(....) method and add the business logic.
Maven / External dependency
- Required dependency. ```xml org.springframework.cloudspring-cloud-starter-gatewayorg.springframework.cloudspring-cloud-starter-netflix-eureka-client

Code / Config changes

Configuration:LoggingGlobalFilter.java

imports
- import some.dependent.resource
- import org.springframework.cloud.gateway.filter.GatewayFilterChain;
- import org.springframework.cloud.gateway.filter.GlobalFilter;
- import org.springframework.web.server.ServerWebExchange;
- import reactor.core.publisher.Mono;

Implement o.s.c.g.filter.GlobalFilter class and filter(...) method.

  @Component
  public class LoggingGlobalFilter implements GlobalFilter {

      private static Logger logger = LoggerFactory.getLogger(LoggingGlobalFilter.class);

      @Override
      public Mono<Void> filter(ServerWebExchange exchange, GatewayFilterChain chain) {

          // log the request
          logger.info("Request -> Method: {}, Path: {}", exchange.getRequest().getMethod(),
                  exchange.getRequest().getPath());

          return chain.filter(exchange);
      }
  }