I've written a very basic Spring Boot 2 application that connects to Zookeeper for service discovery (by using `spring-cloud-starter-zookeeper-discovery`).

The application gets registered at `/services/example-service` with the following value:

```
{"name":"example-service","id":"cb14ad15-4d33-4f1c-a420-29980ddf2fa8","address":"bf3fb9191373","port":8080,"sslPort":null,"payload":{"@class":"org.springframework.cloud.zookeeper.discovery.ZookeeperInstance","id":"application-1","name":"example-service","metadata":{}},"registrationTimeUTC":1524120820273,"serviceType":"DYNAMIC","uriSpec":{"parts":[{"value":"scheme","variable":true},{"value":"://","variable":false},{"value":"address","variable":true},{"value":":","variable":false},{"value":"port","variable":true}]}}

```

The address is an id because I've deployed the stack with Docker.

My Prometheus configuration looks like this:

```
- job_name: 'example-service'
  metrics_path: '/actuator/prometheus'
  serverset_sd_configs:
  - servers:
    - zookeeper:2181
    paths:
    - '/services/example-service'

```

The service discovery page of Prometheus shows the following discovered labels:

```
__address__=":0"  __meta_serverset_endpoint_host=""  __meta_serverset_endpoint_port="0" __meta_serverset_path="/services/example-service/cb14ad15-4d33-4f1c-a420-29980ddf2fa8"  __meta_serverset_shard="0"  __meta_serverset_status="" __metrics_path__="/actuator/prometheus"  __scheme__="http"  job="example-service"

```

Any idea why `__address__` is `:0`?