title: etcd ETCD_ADVERTISE_CLIENT_URLS flag
body: <p>I don't understand what the ETCD_ADVERTISE_CLIENT_URLS flag does despite reading the documentation:</p>
  
  <p><a href="https://coreos.com/etcd/docs/latest/op-guide/configuration.html" rel="noreferrer">https://coreos.com/etcd/docs/latest/op-guide/configuration.html</a></p>
  
  <p>The description states:</p>
  
  <p><em>List of this member's client URLs to advertise to the rest of the cluster. These URLs can contain domain names.</em></p>
  
  <p>I only want a single cluster setup can I leave this flag out of my conf file?</p>
  
  <p>Also if i let the default flag for :</p>
  
  <pre><code>ETCD_LISTEN_CLIENT_URLS="http://localhost:2379"
  </code></pre>
  
  <p>Will etcd only open the service up to the localhost? How can i ensure that any clients outside localhost don't connect to port 2379?</p>