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2. Gateway

The main functionality of Gateway Microservice is to route the incoming requests to the appropriate microservice, therefore, it is the entry point for all the incoming requests. In counterpart, each microservice have to expose their own port and endpoints to the internet, which is not a good practice. The Gateway Microservice will act as a reverse proxy and route the incoming requests to the appropriate microservice. Also, it will also handle the authentication and authorization of the incoming requests.

flowchart LR
    subgraph api [Trusted Layer]
        direction TB
        gateway e2@==> account
        gateway e4@==> others
        account --> db@{ shape: cyl, label: "Database" }
        others --> db
    end
    internet e1@==>|request| gateway:::red
    e1@{ animate: true }
    e2@{ animate: true }
    e4@{ animate: true }
    classDef red fill:#fcc

The key functionalities of Gateway Microservice are:

  • Routing: it will route the incoming requests to the appropriate microservice.
  • Authentication/Authorization: it will handle the authentication and the authorization of the incoming requests.

Gateway-Service

📁 api
└── 📁 gateway-service
    ├── 📁 src
    │   └── 📁 main
    │       ├── 📁 java
    │       │   └── 📁 store
    │       │       └── 📁 gateway
    │       │           ├── 📄 GatewayApplication.java
    │       │           ├── 📄 GatewayResource.java
    │       │           └── 📁 security
    │       │               └── 📄 CorsFilter.java
    │       └── 📁 resources
    │           └── 📄 application.yaml
    ├── 📄 pom.xml
    └── 📄 Dockerfile
Source 
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<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>
    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>3.4.2</version>
        <relativePath/> <!-- lookup parent from repository -->
    </parent>
    <groupId>store</groupId>
    <artifactId>gateway-service</artifactId>
    <version>1.0.0</version>
    <properties>
        <java.version>21</java.version>
        <spring-cloud.version>2024.0.0</spring-cloud.version>
        <maven.compiler.proc>full</maven.compiler.proc>
    </properties>
    <dependencies>
        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-starter-gateway</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-webflux</artifactId>
        </dependency>

        <dependency>
            <groupId>org.projectlombok</groupId>
            <artifactId>lombok</artifactId>
            <optional>true</optional>
        </dependency>

    </dependencies>

    <dependencyManagement>
        <dependencies>
            <dependency>
                <groupId>org.springframework.cloud</groupId>
                <artifactId>spring-cloud-dependencies</artifactId>
                <version>${spring-cloud.version}</version>
                <type>pom</type>
                <scope>import</scope>
            </dependency>
        </dependencies>
    </dependencyManagement>

    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
            </plugin>
        </plugins>
    </build>

</project>

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server:
  port: 8080

spring:
  application:
    name: gateway

  cloud:
    gateway:
      routes:

        # - id: google
        #   uri: https://www.google.com
        #   predicates:
        #     - Path=/google/**

        - id: account
          uri: http://account:8080
          predicates:
            - Path=/account/**

        - id: auth
          uri: http://auth:8080
          predicates:
            - Path=/auth/**

        # - id: exchange
        #   uri: http://exchange:80
        #   predicates:
        #     - Path=/exchange/**

logging:
  level:
    store: ${LOGGING_LEVEL_STORE:debug}

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package store.gateway;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

@SpringBootApplication
public class GatewayApplication {

    public static void main(String[] args) {
        SpringApplication.run(GatewayApplication.class, args);
    }

}

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package store.gateway;

import java.net.InetAddress;
import java.net.UnknownHostException;
import java.util.Map;

import org.springframework.http.HttpStatus;
import org.springframework.http.ResponseEntity;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RestController;

@RestController
public class GatewayResource {

    @GetMapping("/info")
    public ResponseEntity<Map<String, String>> version() {

        String hostname = "hostname can not be resolved";
        try {
            InetAddress addr;
            addr = InetAddress.getLocalHost();
            hostname = addr.getHostName();
        } catch (UnknownHostException ex) { }

        return new ResponseEntity<Map<String, String>>(
            Map.ofEntries(
                Map.entry("hostname", hostname),
                Map.entry("os.arch", System.getProperty("os.arch")),
                Map.entry("os.name", System.getProperty("os.name")),
                Map.entry("os.version", System.getProperty("os.version")),
                Map.entry("file.separator", System.getProperty("file.separator")),
                Map.entry("java.class.path", System.getProperty("java.class.path")),
                Map.entry("java.home", System.getProperty("java.home")),
                Map.entry("java.vendor", System.getProperty("java.vendor")),
                Map.entry("java.vendor.url", System.getProperty("java.vendor.url")),
                Map.entry("java.version", System.getProperty("java.version")),
                Map.entry("line.separator", System.getProperty("line.separator")),
                Map.entry("path.separator", System.getProperty("path.separator")),
                Map.entry("user.dir", System.getProperty("user.dir")),
                Map.entry("user.home", System.getProperty("user.home")),
                Map.entry("user.name", System.getProperty("user.name")),
                Map.entry("jar", new java.io.File(
                    GatewayApplication.class.getProtectionDomain()
                        .getCodeSource()
                        .getLocation()
                        .getPath()
                    ).toString())
            ), HttpStatus.OK
        );
    }

}

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package store.gateway.security;

import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.web.cors.CorsConfiguration;
import org.springframework.web.cors.reactive.CorsWebFilter;
import org.springframework.web.cors.reactive.UrlBasedCorsConfigurationSource;

@Configuration
public class CorsFilter {

    @Bean
    public CorsWebFilter corsWebFilter() {

        CorsConfiguration corsConfig = new CorsConfiguration();
        corsConfig.setAllowCredentials(false);
        corsConfig.addAllowedHeader("*");
        corsConfig.addAllowedMethod("*");
        corsConfig.addAllowedOrigin("*");

        UrlBasedCorsConfigurationSource source = new UrlBasedCorsConfigurationSource();
        source.registerCorsConfiguration("/**", corsConfig);

        return new CorsWebFilter(source);
    }

}

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FROM openjdk:21-slim
VOLUME /tmp
COPY target/*.jar app.jar
ENTRYPOINT ["java","-jar","/app.jar"]