API Gateway ve Service Discovery — İstek Doğru Kapıyı Nasıl Bulur

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spring:
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  application:
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    name: edge-gateway
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  data:
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    redis:
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      host: redis                               # shared by every gateway pod
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  cloud:
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    gateway:
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      server:
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        webflux:              # Spring Cloud Gateway 4.3+; older versions: spring.cloud.gateway.routes
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          routes:
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            - id: accounts
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              uri: lb://accounts-service        # a service name; discovery knows the live instances
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              predicates:
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                - Path=/api/accounts/**
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              filters:
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                - StripPrefix=1
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                - name: Retry
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                  args:
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                    retries: 1
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                    methods: GET                # reading a balance twice is harmless
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            - id: transfers
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              uri: lb://transfer-service
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              predicates:
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                - Path=/api/transfers/**
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                - Method=POST
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              filters:
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                - StripPrefix=1
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                - name: RequestRateLimiter
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                  args:
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                    key-resolver: "#{@customerKeyResolver}"
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                    redis-rate-limiter.replenishRate: 5
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                    redis-rate-limiter.burstCapacity: 10
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                # No Retry here: a timed-out transfer may already have moved the money.

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@Configuration
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class RateLimitConfig {
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    // One bucket per customer, kept in Redis, so three gateway pods do not mean three limits.
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    @Bean
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    KeyResolver customerKeyResolver() {
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        return exchange -> exchange.getPrincipal()
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                .map(Principal::getName)        // JWT subject: the customer number
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                .defaultIfEmpty("anonymous");
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    }
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}

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spring:
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  application:
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    name: accounts-service                      # the name behind lb://accounts-service
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# Eureka registration. On Kubernetes a Service object does this job instead.
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eureka:
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  client:
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    service-url:
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      defaultZone: http://discovery:8761/eureka/
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  instance:
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    prefer-ip-address: true
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    # A dead instance stays on the list until its lease expires: the short gap retry covers.
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    lease-renewal-interval-in-seconds: 10
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    lease-expiration-duration-in-seconds: 30

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# Another way to write it: fixed addresses and a retry on every method.
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spring:
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  cloud:
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    gateway:
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      server:
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        webflux:
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          routes:
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            - id: accounts
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              uri: http://10.0.3.17:8080        # one pod's IP; its replacement comes up elsewhere
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              predicates:
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                - Path=/api/accounts/**
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            - id: transfers
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              uri: http://10.0.4.21:8080
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              predicates:
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                - Path=/api/transfers/**
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              filters:
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                - name: Retry
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                  args:
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                    retries: 3
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                    methods: GET,POST           # a slow transfer can be sent again: a double debit