I have the below architecture, where I am using the spring API gateway to forward the request to the micronaut gcp function.

The product service which is a micronaut gcp function application expose the API doc in below URL

http://localhost:8081/swagger/product-0.0.yml // product micro-service
http://localhost:8082/swagger/payment-0.0.yml // order micro-service
http://localhost:8083/swagger/order-0.0.yml // payment micro-service

The api-gateway, is a spring application with the below dependency

dependencies {
    implementation("org.springframework.cloud:spring-cloud-starter-gateway")
    implementation("org.springdoc:springdoc-openapi-starter-webflux-ui:2.5.0")
}

I have the below configuration in the yml

spring:
  application:
    name: apigateway
  cloud:
    gateway:
      routes:
        - id: product-service
          uri:
            ${PRODUCT_SERVICE_URL:http://localhost:8081}
          predicates:
            - Path=/product/**, /swagger/**
        - id: order-service
          uri:
            ${ORDER_SERVICE_URL:http://localhost:8082}
          predicates:
            - Path=/order/**, /swagger/**

And a Bean configuration as

@Configuration
public class SwaggerConfig {

    @Bean
    public Set<SwaggerUrl> openApiGroups(
            RouteDefinitionLocator locator,
            SwaggerUiConfigParameters swaggerUiParameters) {
        Set<SwaggerUrl> urls = new HashSet<>();
        List<RouteDefinition> definitions = locator.getRouteDefinitions().collectList().block();
        Objects.requireNonNull(definitions).stream().filter(routeDefinition -> routeDefinition.getId().matches(".*-service"))
                .forEach(routeDefinition -> {
                    String name = routeDefinition.getId().replaceAll("-service", "");
                    SwaggerUrl swaggerUrl = new SwaggerUrl(name, String.format("/swagger/%s-0.0.yml",name), null);
                    urls.add(swaggerUrl);
                });
        swaggerUiParameters.setUrls(urls);
        return urls;
    }
}

The swagger-ui in the api-gateway is loaded, but the reference API is loaded. I am not using any discovery service, since it is a serverless application. They will be hosted as GCP function.