Implementing a Spring Cloud Gateway with Nacos for Dynamic Service Discovery and Load Balancing

This article provides a step‑by‑step guide to building a Spring Cloud Gateway integrated with Nacos as a registration and configuration center, covering Nacos installation, project setup with Spring Boot 2.7, dependency configuration, bootstrap and environment YAML files, route definition, and handling dynamic service instance changes.

It explains how to start Nacos in standalone mode using java -jar -Dnacos.standalone=true nacos-server.jar, configure Spring Cloud Alibaba Nacos discovery and config dependencies, and set up common and test‑specific configuration files for Redis and Nacos connection details.

It demonstrates defining routes via a

@Bean public RouteLocator routeLocator(RouteLocatorBuilder builder) { ... }

bean, showing how path and uri predicates work, and discusses the importance of service instance awareness, illustrating the problem of stale load‑balancer caches when instances go offline.

To solve this, the article introduces a listener for Nacos InstancesChangeEvent that evicts the corresponding cache entry, ensuring the gateway refreshes its service list in real time. The listener is implemented as a static component extending Subscriber<InstancesChangeEvent> and uses the Spring Cache manager to evict the service cache.

Code examples are provided for Nacos startup command, Maven <parent>...</parent> snippet, bootstrap.yaml, test environment application.yaml, route locator bean, and the event listener implementation.