Why Does Consul Register Only One Instance in Spring Cloud Finchley? Solutions Revealed

Due to the lack of Etcd support in Spring Cloud, most users still use Eureka or Consul for service registration. This article discusses a serious pitfall when using Spring Cloud Finchley with Consul 1.2.x: only one instance is registered.

Problem Interpretation

Problem: The issue may not appear during development, but when deploying multiple instances online, Consul shows only a single instance.

Cause: Spring Cloud Consul builds the instance ID as {spring.application.name}-{server.port}. When the port does not change, the IDs are identical. Older Consul versions treated identical IDs with different addresses as distinct, but Consul 1.2.x uses the instance ID as a unique identifier, leading to the problem.

Solution

Knowing the cause, two concrete solutions are presented:

Method 1: Configure a new instance‑ID rule

Set spring.cloud.consul.discovery.instance-id to a custom pattern, e.g. using a random number:

spring.cloud.consul.discovery.instance-id=${spring.application.name}-${random.int[10000,99999]}

Method 2: Extend ConsulServiceRegistry

Override the register method to construct a globally unique ID, such as “service‑name‑ip‑port”. Example implementation:

public class MyConsulServiceRegistry extends ConsulServiceRegistry {
    public MyConsulServiceRegistry(ConsulClient client, ConsulDiscoveryProperties properties,
                                   TtlScheduler ttlScheduler, HeartbeatProperties heartbeatProperties) {
        super(client, properties, ttlScheduler, heartbeatProperties);
    }

    @Override
    public void register(ConsulRegistration reg) {
        reg.getService().setId(reg.getService().getName() + "-" + reg.getService().getAddress() + "-" + reg.getService().getPort());
        super.register(reg);
    }
}

By concatenating service name, IP address, and port, each instance receives a truly unique ID, ensuring proper registration in Consul.