TUN-6639: Validate cyclic ingress configuration

It is currently possible to set cloudflared to proxy to the hostname
that traffic is ingressing from as an origin service. This change checks
for this configuration error and prompts a change.

ingress/ingress.go

@@ -232,6 +232,10 @@ func validateIngress(ingress []config.UnvalidatedIngressRule, defaults OriginReq
 			} else {
 				service = newTCPOverWSService(u)
 			}
+
+			if u.Hostname() == r.Hostname {
+				return Ingress{}, fmt.Errorf("Cyclic Ingress configuration: Hostname:%s points to service:%s.", r.Hostname, r.Service)
+			}
 		}
 
 		if err := validateHostname(r, i, len(ingress)); err != nil {

ingress/ingress_test.go

@@ -404,6 +404,16 @@ ingress:
    service: https://localhost:8000
  - hostname: "*"
    service: https://localhost:8001
+`},
+			wantErr: true,
+		},
+		{
+			name: "Cyclic hostname definition",
+			args: args{rawYAML: `
+ingress:
+ - hostname: "test.example.com"
+   service: https://test.example.com
+ - service: http_status_404
 `},
 			wantErr: true,
 		},