[tmpnet] Avoid port forwarding when running in a kube cluster (#3997)

Author: maru-ava

tests/fixture/tmpnet/kube_runtime.go

@@ -144,8 +144,10 @@ func (p *KubeRuntime) GetLocalURI(ctx context.Context) (string, func(), error) {
 		}
 	}
 
-	// TODO(marun) Detect whether this test code is running inside the cluster
-	//             and use the URI directly
+	// Use direct pod URI if running inside the cluster
+	if isRunningInCluster() {
+		return p.node.URI, func() {}, nil
+	}
 
 	port, stopChan, err := p.forwardPort(ctx, config.DefaultHTTPPort)
 	if err != nil {
@@ -164,8 +166,10 @@ func (p *KubeRuntime) GetLocalStakingAddress(ctx context.Context) (netip.AddrPor
 		}
 	}
 
-	// TODO(marun) Detect whether this test code is running inside the cluster
-	//             and use the URI directly
+	// Use direct pod staking address if running inside the cluster
+	if isRunningInCluster() {
+		return p.node.StakingAddress, func() {}, nil
+	}
 
 	port, stopChan, err := p.forwardPort(ctx, config.DefaultStakingPort)
 	if err != nil {
@@ -837,3 +841,11 @@ func configureExclusiveScheduling(template *corev1.PodTemplateSpec, labelKey str
 		},
 	}
 }
+
+// isRunningInCluster detects if this code is running inside a Kubernetes cluster
+// by checking for the presence of the service account token that's automatically
+// mounted in every pod.
+func isRunningInCluster() bool {
+	_, err := os.Stat("/var/run/secrets/kubernetes.io/serviceaccount/token")
+	return err == nil
+}