Load balancer does not have available server for client: meeting

Question

While I am trying to reach the service meeting via Zuul gateway, Zuul is unable to forward the request to the respective service. The following errors are what I am

Answer 1

Short answer

ribbon:
  eureka:
    enabled: false

Spring Cloud Netflix Zuul uses Netflix’s Ribbon to perform client-side load balancing, and by default, Ribbon would use Netflix Eureka for service discovery. You are skipping service discovery, so you've set ribbon.eureka.enabled to false. Since Ribbon now can’t use Eureka to look up services, you must specify an url for the meeting service:

meeting:
  ribbon:
    listOfServers: localhost:8080

Expanded answer

I will make it more clear for you.

The dependency org.springframework.cloud:spring-cloud-starter-netflix-zuul, which you are currently using in the gatekeeper project, has several compile dependencies:

com.netflix.zuul:zuul-core
org.springframework.boot:spring-boot-starter-web        
org.springframework.boot:spring-boot-starter-actuator       
org.springframework.cloud:spring-cloud-netflix-zuul
org.springframework.cloud:spring-cloud-starter      
org.springframework.cloud:pring-cloud-starter-netflix-hystrix
org.springframework.cloud:spring-cloud-starter-netflix-ribbon
org.springframework.cloud:spring-cloud-starter-netflix-archaius

As you see, it constitutes many components gathered around the com.netflix.zuul:zuul-core module (including Eureka for instance discovery and Ribbon for routing):

When you are launching the gatekeeper application, the default ZuulProxyAutoConfiguration configuration is being applied. It imports Ribbon configuration classes:

@Configuration
@Import({ RibbonCommandFactoryConfiguration.RestClientRibbonConfiguration.class,
        RibbonCommandFactoryConfiguration.OkHttpRibbonConfiguration.class,
        RibbonCommandFactoryConfiguration.HttpClientRibbonConfiguration.class,
        HttpClientConfiguration.class })
@ConditionalOnBean(ZuulProxyMarkerConfiguration.Marker.class)
public class ZuulProxyAutoConfiguration extends ZuulServerAutoConfiguration { ... }

HttpClientRibbonConfiguration, in turn, initialises RibbonLoadBalancingHttpClient which is responsible for the error messages you saw.

That RibbonLoadBalancingHttpClient by default utilises ZoneAwareLoadBalancer which comes from a com.netflix.ribbon:ribbon-loadbalancer package:

By default Zuul load balances using the ZoneAwareLoadBalancer from Ribbon. The algorithm is a round robin of the instances available in discovery, with availability zone success tracking for resiliency. The load balancer will keep stats for each zone and will drop a zone if the failure rates are above a configurable threshold.

If you want to use your own custom load balancer you can set the NFLoadBalancerClassName property for that Ribbon client namespace or override the getLoadBalancerClass() method in the DefaultClientChannelManager. Note that your class should extend DynamicServerListLoadBalancer.

It explains that Zuul delegates routing and load balancing work to Ribbon components and proves that you are actually using Ribbon in the gatekeeper project.

Unless you choose a different load balancer, you should go for my original answer.
I hope it will help.