Routes and Predicates

Routes in application.yml

A route has an id, a destination uri, predicates (conditions to match) and optional filters. lb:// means "look the name up in the registry and load-balance":

api-gateway application.yml

application.yml

server:
  port: 8080

spring:
  application:
    name: api-gateway
  cloud:
    gateway:
      routes:
        - id: product-service
          uri: lb://product-service
          predicates:
            - Path=/api/products/**,/api/categories/**

        - id: order-service
          uri: lb://order-service
          predicates:
            - Path=/api/orders/**

        - id: user-service
          uri: lb://user-service
          predicates:
            - Path=/api/users/**,/api/cart/**

        - id: payment-service
          uri: lb://payment-service
          predicates:
            - Path=/api/payments/**
            - Method=GET,POST

eureka:
  client:
    service-url:
      defaultZone: http://localhost:8761/eureka/

Example output

$ curl localhost:8080/api/products/7
HTTP/1.1 200 OK
{"id":7,"name":"boAt Rockerz 450","price":1499.00,"stock":120,"category":"Audio"}

$ curl localhost:8080/api/orders/1001
HTTP/1.1 200 OK
{"orderId":1001,"status":"CREATED","total":2998.00}

$ curl localhost:8080/api/unknown
HTTP/1.1 404 Not Found

Common Predicates

Predicate	Matches when	Example
`Path`	URL path matches a pattern	`Path=/api/orders/**`
`Method`	HTTP method	`Method=GET,POST`
`Header`	Header matches a regex	`Header=X-Client, android\|ios`
`Query`	Query parameter present / matches	`Query=version, v2`
`Host`	Host header	`Host=**.shopease.in`
`After` / `Before` / `Between`	Time window	Open a sale route at a fixed time
`Weight`	Split traffic by percentage	90% v1, 10% v2 (canary)

Routes in Java

The same routes can be built with the Java DSL. Handy when routes need logic or are generated:

@Configuration
class GatewayRoutes {

    @Bean
    RouteLocator shopEaseRoutes(RouteLocatorBuilder builder) {
        return builder.routes()
                .route("product-service", r -> r
                        .path("/api/products/**", "/api/categories/**")
                        .uri("lb://product-service"))
                .route("order-service-v2-canary", r -> r
                        .path("/api/orders/**")
                        .and().weight("orders", 10)          // 10% of order traffic
                        .uri("lb://order-service-v2"))
                .route("order-service", r -> r
                        .path("/api/orders/**")
                        .and().weight("orders", 90)          // 90% of order traffic
                        .uri("lb://order-service"))
                .build();
    }
}

Example

Check what the gateway loaded (needs management.endpoints.web.exposure.include: gateway):

curl -s localhost:8080/actuator/gateway/routes | jq ".[].route_id"

Example output

"product-service"
"order-service-v2-canary"
"order-service"
"user-service"
"payment-service"