use loopback instead of hardcoding IPs

backend/controller/admin/cmd_client.go

@@ -3,6 +3,7 @@ package admin
 import (
 	"context"
 	"errors"
+	"net"
 	"net/url"
 
 	"connectrpc.com/connect"
@@ -62,5 +63,14 @@ func isConnectUnavailableError(err error) bool {
 
 func isEndpointLocal(endpoint *url.URL) bool {
 	h := endpoint.Hostname()
-	return h == "localhost" || h == "127.0.0.1"
+	ips, err := net.LookupIP(h)
+	if err != nil {
+		panic(err.Error())
+	}
+	for _, netip := range ips {
+		if netip.IsLoopback() {
+			return true
+		}
+	}
+	return false
 }

backend/controller/admin/cmd_client_test.go

@@ -0,0 +1,45 @@
+package admin
+
+import (
+	"net/url"
+	"testing"
+
+	"github.com/alecthomas/assert/v2"
+)
+
+func TestIsEndpointLocal(t *testing.T) {
+	tests := []struct {
+		Name     string
+		Endpoint string
+		Want     bool
+	}{
+		{
+			Name:     "DefaultLocalhost",
+			Endpoint: "http://localhost:8892",
+			Want:     true,
+		},
+		{
+			Name:     "NumericLocalhost",
+			Endpoint: "http://127.0.0.1:8892",
+			Want:     true,
+		},
+		{
+			Name:     "TooLow",
+			Endpoint: "http://126.255.255.255:8892",
+			Want:     false,
+		},
+		{
+			Name:     "TooHigh",
+			Endpoint: "http://128.0.0.1:8892",
+			Want:     false,
+		},
+	}
+
+	for _, test := range tests {
+		t.Run(test.Name, func(t *testing.T) {
+			u, err := url.Parse(test.Endpoint)
+			assert.NoError(t, err)
+			assert.Equal(t, isEndpointLocal(u), test.Want)
+		})
+	}
+}