ugh external service traffic.
This blog will cover how you can use these augmented metrics to monitor all
external service traffic.</p><p>The Istio control plane configures the sidecar proxy with
predefined clusters called BlackHoleCluster and Passthrough which block or
allow all traffic respectively. To understand these clusters, let&rsquo;s start with
what external and internal services mean in the context of Istio service mesh.</p><h2 id=external-and-internal-services>External and internal services</h2><