Spring Cloud Netflix：ribbon.NIWSServerListClassName与listOfServers有何区别？

Hey there! Let's break down the key differences between these two Ribbon configuration properties you're using with Eureka, plus clear up a small mix-up in your second config that's worth noting.

1. NIWSServerListClassName #

• Core Purpose: This property lets you specify the fully qualified class name of a class that implements Ribbon's ServerList interface. This class is responsible for fetching the list of available service instances for Ribbon to load balance across.
• Your Use Case: The class you're using—com.netflix.niws.loadbalancer.DiscoveryEnabledNIWSServerList—is the official implementation that integrates directly with Eureka. It will automatically pull the latest list of other-service instances from your Eureka Server, and respect the ServerListRefreshInterval: 1000 setting to refresh that list every 1 second. This means Ribbon will dynamically adapt as instances are added, removed, or go offline.
• Best For: This is the standard choice when you're using Eureka (or any service discovery tool) in a dynamic microservices environment, where service instances change over time.

2. listOfServers #

• Core Purpose: This property is for hardcoding a static list of service instance addresses, formatted as comma-separated host:port values (e.g., localhost:8080,192.168.0.10:8081). Ribbon will only use these fixed addresses, with no connection to service discovery.
• Important Note: Your second configuration has a mistake here—you've set the value to a class name instead of server addresses! The reason it still works is because you have eureka.enabled: true enabled, which takes priority. Ribbon falls back to using Eureka's service discovery instead of your invalid listOfServers value. If you disabled Eureka (eureka.enabled: false), this config would fail entirely.
• Best For: Use this only when you don't need dynamic service discovery—like in a test environment with fixed instances, or for simple, static services that never change.

Quick Summary #

• NIWSServerListClassName: Dynamic instance fetching via service discovery (Eureka in your case), perfect for dynamic microservices.
• listOfServers: Static hardcoded instances, disconnected from service discovery, for fixed, unchanging service endpoints.
• Your second config works only because Eureka is enabled and takes precedence over the invalid listOfServers value.

内容的提问来源于stack exchange，提问作者narendra-choudhary