How does routing occur between instances of the ACL service with different addresses?

Routing between ACL service instances with different addresses is usually implemented using service discovery and load balancers. In a distributed system, each instance registers in a registry (e.g., Consul, Zookeeper, Eureka), which stores the current list of available addresses.

When a client or proxy accesses the ACL service, it retrieves the list of instances from the registry and distributes requests among them according to a chosen strategy (round-robin, least connections, consistent hashing, etc.).

In Java, Spring Cloud Netflix Eureka is often used for service discovery, along with Ribbon or Spring Cloud LoadBalancer for load balancing. An API Gateway can also be used to route requests to the appropriate instance.

If services communicate via gRPC, the built-in gRPC load balancer can use the list of addresses to distribute the load.

Thus, routing is ensured by dynamic instance discovery and load balancing, which allows scaling the ACL service and ensuring fault tolerance.