WebSocket Load‑Balancing Concept Library for Microservice Clusters

WebSocket works well in monolithic applications, but in a microservice architecture a client connected to service instance A may miss messages sent by instance B because the load‑balanced gateway may route the client to different instances.

To address this, the author created a library that, with a single annotation @EnableWebSocketLoadBalanceConcept (plus standard Spring annotations), configures automatic message forwarding between service instances.

Usage example:

@EnableWebSocketLoadBalanceConcept
@EnableDiscoveryClient
@SpringBootApplication
public class AServiceApplication {
    public static void main(String[] args) {
        SpringApplication.run(AServiceApplication.class, args);
    }
}

In a controller you can inject the concept and send messages across instances:

@RestController
@RequestMapping("/ws")
public class WsController {
    @Autowired
    private WebSocketLoadBalanceConcept concept;

    @RequestMapping("/send")
    public void send(@RequestParam String msg) {
        concept.send(msg);
    }
}

The design abstracts a Connection interface, with implementations such as WebSocketConnection or TCPConnection . A ConnectionSubscriber forwards messages, while a ConnectionServerManager discovers service instances via Spring Cloud DiscoveryClient (Eureka, Nacos, etc.).

The connection flow establishes mutual connections between instances, exchanges instance‑info messages, and maintains heart‑beat checks with automatic reconnection, ensuring reliable message propagation even under network instability.

Connections are classified into real client connections and forwarding connections, managed by a unified repository. Message sending uses a ConnectionSelector to choose target connections; built‑in selectors like UserSelector and PathSelector enable precise delivery to specific users or topics.

Additional features include metadata on connections, header‑based routing, and optional use of external transports (HTTP, MQ) for higher reliability.

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