te that the <code>destination_service_name</code> label is set to PassthroughCluster to
indicate that this cluster was hit and the <code>destination_service</code> is set to the
host of the external service.</p></li><li><p>TCP proxy virtual listener - If the external service port doesn&rsquo;t map to any
HTTP based service ports within the cluster, this listener is invoked and
<code>istio_tcp_connections_closed_total</code> is the metric that will be increased:</p><pre><code class=language-json data-expandl