feat: Add option to define which DNS server a DNS monitor queries (#2389)

agent/network_monitor_probe.go

@@ -28,7 +28,7 @@ func networkMonitorProbe(client *http.Client) monitorProbe {
 		case "http":
 			return monitorHTTP(ctx, client, config.Target)
 		case "dns":
-			return monitorDNS(ctx, config.Target)
+			return monitorDNS(ctx, config.Target, config.Server)
 		default:
 			return -1, fmt.Errorf("unknown monitor protocol: %s", config.Protocol)
 		}
@@ -73,19 +73,43 @@ func monitorTCP(ctx context.Context, target string, port uint16) (int64, error)
 	return -1, err
 }
 
-// monitorDNS measures DNS resolution response time in microseconds. Returns -1 and an error on failure.
-func monitorDNS(ctx context.Context, target string) (int64, error) {
+// monitorDNS measures DNS resolution response time in microseconds. If server is
+// non-empty, the lookup is sent to that DNS server (host or host:port, default
+// port 53) instead of the system resolver. Returns -1 and an error on failure.
+func monitorDNS(ctx context.Context, target, server string) (int64, error) {
 	ctx, cancel := context.WithTimeout(ctx, 3*time.Second)
 	defer cancel()
 
+	resolver := net.DefaultResolver
+	if server != "" {
+		resolver = dnsResolverForServer(server)
+	}
+
 	start := time.Now()
-	ips, err := net.DefaultResolver.LookupHost(ctx, target)
+	ips, err := resolver.LookupHost(ctx, target)
 	if err != nil || len(ips) == 0 {
 		return -1, err
 	}
 	return time.Since(start).Microseconds(), nil
 }
 
+// dnsResolverForServer builds a resolver that sends lookups to the given DNS
+// server address instead of the system resolver. server may be a bare host or
+// host:port; when no port is given, the standard DNS port 53 is used.
+func dnsResolverForServer(server string) *net.Resolver {
+	address := server
+	if _, _, err := net.SplitHostPort(server); err != nil {
+		address = net.JoinHostPort(server, "53")
+	}
+	return &net.Resolver{
+		PreferGo: true,
+		Dial: func(ctx context.Context, network, _ string) (net.Conn, error) {
+			var dialer net.Dialer
+			return dialer.DialContext(ctx, network, address)
+		},
+	}
+}
+
 // monitorHTTP measures HTTP GET request response in microseconds. Returns -1 and an error on failure.
 func monitorHTTP(ctx context.Context, client *http.Client, url string) (int64, error) {
 	if client == nil {

agent/network_monitor_test.go

@@ -376,15 +376,79 @@ func tcpMonitorTestResolver(ips []string) *net.Resolver {
 	}}
 }
 
+// udpDNSTestServer starts a UDP server on loopback that answers A queries with the
+// given IPs, and returns its listen address (host:port).
+func udpDNSTestServer(t *testing.T, ips []string) string {
+	t.Helper()
+	conn, err := net.ListenUDP("udp", &net.UDPAddr{IP: net.ParseIP("127.0.0.1")})
+	require.NoError(t, err)
+	t.Cleanup(func() { conn.Close() })
+
+	go func() {
+		buf := make([]byte, 512)
+		for {
+			n, addr, err := conn.ReadFromUDP(buf)
+			if err != nil {
+				return
+			}
+			var msg dnsmessage.Message
+			if err := msg.Unpack(buf[:n]); err != nil {
+				continue
+			}
+			msg.Header.Response = true
+			msg.Header.RecursionAvailable = true
+			for _, question := range msg.Questions {
+				if question.Type != dnsmessage.TypeA {
+					continue
+				}
+				for _, ip := range ips {
+					msg.Answers = append(msg.Answers, dnsmessage.Resource{
+						Header: dnsmessage.ResourceHeader{Name: question.Name, Type: dnsmessage.TypeA, Class: dnsmessage.ClassINET},
+						Body:   &dnsmessage.AResource{A: [4]byte(net.ParseIP(ip).To4())},
+					})
+				}
+			}
+			packet, err := msg.Pack()
+			if err != nil {
+				continue
+			}
+			_, _ = conn.WriteToUDP(packet, addr)
+		}
+	}()
+
+	return conn.LocalAddr().String()
+}
+
 func TestMonitorDNS(t *testing.T) {
 	t.Run("success", func(t *testing.T) {
-		responseUs, err := monitorDNS(context.Background(), "localhost")
+		responseUs, err := monitorDNS(context.Background(), "localhost", "")
 		require.NoError(t, err)
 		assert.GreaterOrEqual(t, responseUs, int64(0))
 	})
 
 	t.Run("lookup failure", func(t *testing.T) {
-		responseUs, err := monitorDNS(context.Background(), "")
+		responseUs, err := monitorDNS(context.Background(), "", "")
+		assert.Equal(t, int64(-1), responseUs)
+		require.Error(t, err)
+	})
+
+	t.Run("custom server", func(t *testing.T) {
+		serverAddr := udpDNSTestServer(t, []string{"192.0.2.10"})
+		responseUs, err := monitorDNS(context.Background(), "example.test.", serverAddr)
+		require.NoError(t, err)
+		assert.GreaterOrEqual(t, responseUs, int64(0))
+	})
+
+	t.Run("custom server without port defaults to 53", func(t *testing.T) {
+		resolver := dnsResolverForServer("127.0.0.1")
+		conn, err := resolver.Dial(context.Background(), "udp", "")
+		require.NoError(t, err)
+		defer conn.Close()
+		assert.Equal(t, "127.0.0.1:53", conn.RemoteAddr().String())
+	})
+
+	t.Run("custom server unreachable", func(t *testing.T) {
+		responseUs, err := monitorDNS(context.Background(), "example.test.", "127.0.0.1:1")
 		assert.Equal(t, int64(-1), responseUs)
 		require.Error(t, err)
 	})
@@ -479,7 +543,7 @@ func TestMonitorResolutionCancellation(t *testing.T) {
 				case "tcp":
 					_, err = monitorTCP(ctx, "monitor-cancellation.invalid.", 80)
 				case "dns":
-					_, err = monitorDNS(ctx, "monitor-cancellation.invalid.")
+					_, err = monitorDNS(ctx, "monitor-cancellation.invalid.", "")
 				case "icmp":
 					_, err = monitorICMP(ctx, "monitor-cancellation.invalid.")
 				}

internal/entities/monitor/monitor.go

@@ -25,6 +25,9 @@ type Config struct {
 	Protocol string `cbor:"2,keyasint"` // "icmp", "tcp", "http", or "dns"
 	Port     uint16 `cbor:"3,keyasint,omitempty"`
 	Interval uint16 `cbor:"4,keyasint"` // seconds
+	// Server is the DNS server to query (host or host:port, default port 53).
+	// Only used when Protocol is "dns"; empty means use the system resolver.
+	Server string `cbor:"5,keyasint,omitempty"`
 }
 
 // CertInfo holds details of the leaf TLS certificate presented by a target.

internal/hub/network_monitors.go

@@ -17,6 +17,10 @@ func generateMonitorID(systemId string, config monitor.Config) string {
 	if config.Protocol == "tcp" {
 		args = append(args, strconv.FormatUint(uint64(config.Port), 10))
 	}
+	// only use server for DNS monitors, so the same target queried via different servers gets distinct monitors
+	if config.Protocol == "dns" {
+		args = append(args, config.Server)
+	}
 	return systems.MakeStableHashId(args...)
 }
 
@@ -53,10 +57,15 @@ func bindNetworkMonitorsEvents(hub *Hub) {
 	// record with the new ID and delete the old one. Otherwise, just update the existing monitor on the agent.
 	hub.OnRecordUpdateRequest("network_monitors").BindFunc(func(e *core.RecordRequestEvent) error {
 		systemID := e.Record.GetString("system")
+		protocol := e.Record.GetString("protocol")
 		// only tcp uses port - set other protocols port to zero
-		if e.Record.GetString("protocol") != "tcp" {
+		if protocol != "tcp" {
 			e.Record.Set("port", 0)
 		}
+		// only dns uses server - clear it for other protocols
+		if protocol != "dns" {
+			e.Record.Set("server", "")
+		}
 		ID := generateMonitorID(systemID, *monitorConfigFromRecord(e.Record))
 		if ID != e.Record.Id {
 			newRecord := copyMonitorToNewRecord(e.Record, ID)
@@ -103,6 +112,7 @@ func monitorConfigFromRecord(record *core.Record) *monitor.Config {
 		Protocol: record.GetString("protocol"),
 		Port:     uint16(record.GetInt("port")),
 		Interval: uint16(record.GetInt("interval")),
+		Server:   record.GetString("server"),
 	}
 }
 
@@ -127,7 +137,7 @@ func copyMonitorToNewRecord(oldRecord *core.Record, newID string) *core.Record {
 	collection := oldRecord.Collection()
 	newRecord := core.NewRecord(collection)
 	newRecord.Id = newID
-	fields := []string{"system", "target", "protocol", "port", "interval", "enabled"}
+	fields := []string{"system", "target", "protocol", "port", "server", "interval", "enabled"}
 	for _, field := range fields {
 		newRecord.Set(field, oldRecord.Get(field))
 	}

internal/hub/network_monitors_test.go

@@ -174,6 +174,39 @@ func TestGenerateMonitorID(t *testing.T) {
 			},
 			expected: "84167969",
 		},
+		{
+			name:     "DNS monitor on example.com with server 1.1.1.1",
+			systemID: "sys999",
+			config: monitor.Config{
+				Protocol: "dns",
+				Target:   "example.com",
+				Server:   "1.1.1.1",
+				Interval: 30,
+			},
+			expected: "2175898b",
+		},
+		{
+			name:     "DNS monitor on example.com with different server",
+			systemID: "sys999",
+			config: monitor.Config{
+				Protocol: "dns",
+				Target:   "example.com",
+				Server:   "8.8.8.8",
+				Interval: 30,
+			},
+			expected: "ebcd8b33",
+		},
+		{
+			name:     "DNS monitor on example.com with no server (system resolver)",
+			systemID: "sys999",
+			config: monitor.Config{
+				Protocol: "dns",
+				Target:   "example.com",
+				Server:   "",
+				Interval: 30,
+			},
+			expected: "19476a7",
+		},
 	}
 
 	for _, tt := range tests {
@@ -199,6 +232,7 @@ func TestCopyMonitorToNewRecordDropsResultFields(t *testing.T) {
 		"target":   "https://example.com",
 		"protocol": "http",
 		"port":     443,
+		"server":   "1.1.1.1",
 		"interval": 60,
 		"enabled":  true,
 		"res":      1200,
@@ -216,6 +250,7 @@ func TestCopyMonitorToNewRecordDropsResultFields(t *testing.T) {
 	assert.Equal(t, "https://example.com", newRecord.GetString("target"))
 	assert.Equal(t, "http", newRecord.GetString("protocol"))
 	assert.Equal(t, 443, newRecord.GetInt("port"))
+	assert.Equal(t, "1.1.1.1", newRecord.GetString("server"))
 	assert.True(t, newRecord.GetBool("enabled"))
 	assert.Contains(t, []string{"", "null"}, newRecord.GetString("certInfo"))
 	assert.Zero(t, newRecord.GetFloat("res"))

internal/migrations/1790273174_network_monitor_server.go

@@ -0,0 +1,24 @@
+package migrations
+
+import (
+	"github.com/pocketbase/pocketbase/core"
+	m "github.com/pocketbase/pocketbase/migrations"
+)
+
+func init() {
+	m.Register(func(app core.App) error {
+		collection, err := app.FindCollectionByNameOrId("network_monitors")
+		if err != nil {
+			return err
+		}
+		collection.Fields.Add(&core.TextField{Id: "nm_server", Name: "server", Max: 260})
+		return app.Save(collection)
+	}, func(app core.App) error {
+		collection, err := app.FindCollectionByNameOrId("network_monitors")
+		if err != nil {
+			return err
+		}
+		collection.Fields.RemoveByName("server")
+		return app.Save(collection)
+	})
+}

internal/site/src/components/network-monitors-table/monitor-dialog.tsx

@@ -37,6 +37,7 @@ type MonitorValues = {
 	target: string
 	protocol: MonitorProtocol
 	port: number
+	server: string
 	interval: string
 }
 
@@ -44,7 +45,7 @@ type NormalizedMonitorValues = Omit<MonitorValues, "system" | "interval"> & {
 	interval: number
 }
 
-type BulkMonitorLineSource = Pick<NetworkMonitorRecord, "target" | "protocol" | "port" | "interval">
+type BulkMonitorLineSource = Pick<NetworkMonitorRecord, "target" | "protocol" | "port" | "interval" | "server">
 
 const defaultInterval = 30
 
@@ -59,6 +60,7 @@ const NormalizedMonitorValuesSchema = v.pipe(
 		target: v.pipe(v.string(), v.trim(), v.nonEmpty("target is required")),
 		protocol: MonitorProtocolSchema,
 		port: v.number(),
+		server: v.pipe(v.string(), v.trim()),
 		interval: MonitorIntervalSchema,
 	}),
 	v.transform((input): NormalizedMonitorValues => {
@@ -78,6 +80,8 @@ const NormalizedMonitorValuesSchema = v.pipe(
 			target: protocol === "http" ? httpTarget : input.target,
 			protocol,
 			port,
+			// Only DNS monitors use a custom server; clear it for other protocols.
+			server: protocol === "dns" ? input.server : "",
 			interval: input.interval,
 		}
 	}),
@@ -100,6 +104,7 @@ const BulkMonitorSchema = v.object({
 	protocol: v.optional(v.pipe(v.string(), v.trim())),
 	port: v.optional(v.pipe(v.string(), v.trim())),
 	interval: v.optional(v.pipe(v.string(), v.trim())),
+	server: v.optional(v.pipe(v.string(), v.trim())),
 })
 
 function normalizeHttpTarget(target: string, port = 0) {
@@ -152,18 +157,19 @@ function buildMonitorPayload(values: MonitorValues, enabled = true) {
 	return payload
 }
 
-type MonitorIdentity = Pick<MonitorValues, "system" | "target" | "protocol" | "port">
-function getMonitorIdentityKey({ system, target, protocol, port }: MonitorIdentity) {
-	return `${system}${target}${protocol}${port}`
+type MonitorIdentity = Pick<MonitorValues, "system" | "target" | "protocol" | "port" | "server">
+function getMonitorIdentityKey({ system, target, protocol, port, server }: MonitorIdentity) {
+	return `${system}${target}${protocol}${port}${protocol === "dns" ? server : ""}`
 }
 
 function parseBulkMonitorLine(line: string, lineNumber: number, system: string) {
-	const [rawTarget = "", rawProtocol = "", rawPort = "", rawInterval = ""] = line.split(",")
+	const [rawTarget = "", rawProtocol = "", rawPort = "", rawInterval = "", rawServer = ""] = line.split(",")
 	const parsed = v.safeParse(BulkMonitorSchema, {
 		target: rawTarget,
 		protocol: rawProtocol,
 		port: rawPort,
 		interval: rawInterval,
+		server: rawServer,
 	})
 	if (!parsed.success) {
 		throw new Error(`Line ${lineNumber}: ${parsed.issues[0]?.message || "invalid monitor entry"}`)
@@ -176,6 +182,7 @@ function parseBulkMonitorLine(line: string, lineNumber: number, system: string)
 		target: parsed.output.target,
 		protocol,
 		port: parsed.output.port ? Number(parsed.output.port) : 0,
+		server: parsed.output.server || "",
 		interval: parsed.output.interval || `${defaultInterval}`,
 	})
 }
@@ -183,7 +190,8 @@ function parseBulkMonitorLine(line: string, lineNumber: number, system: string)
 export function formatBulkMonitorLine(monitor: BulkMonitorLineSource) {
 	const port = monitor.protocol !== "tcp" || monitor.port === 443 ? "" : `${monitor.port}`
 	const interval = monitor.interval === defaultInterval ? "" : `${monitor.interval}`
-	return trimTrailingEmptyFields([monitor.target, monitor.protocol, port, interval]).join(",")
+	const server = monitor.protocol !== "dns" ? "" : monitor.server
+	return trimTrailingEmptyFields([monitor.target, monitor.protocol, port, interval, server]).join(",")
 }
 
 function SystemMultiSelect({
@@ -498,7 +506,7 @@ export function AddMonitorDialog({ systemId, monitors }: { systemId?: string; mo
 							<Trans>Bulk Add {{ foo: t`Network Monitors` }}</Trans>
 						</SheetTitle>
 						<SheetDescription>
-							<Trans>target[,protocol[,port[,interval]]]</Trans>
+							<Trans>target[,protocol[,port[,interval[,server]]]]</Trans>
 						</SheetDescription>
 					</SheetHeader>
 					<form ref={bulkFormRef} onSubmit={handleBulkSubmit} className="flex h-full flex-col overflow-hidden">
@@ -532,11 +540,16 @@ export function AddMonitorDialog({ systemId, monitors }: { systemId?: string; mo
 										}
 									}}
 									className="font-mono grow text-sm bg-card"
-									placeholder={["1.1.1.1", "example.com,tcp", "https://example.com,http,,60"].join("\n")}
+									placeholder={[
+										"1.1.1.1",
+										"example.com,tcp",
+										"https://example.com,http,,60",
+										"example.com,dns,,,1.1.1.1",
+									].join("\n")}
 									required
 								/>
 								<p className="text-xs text-muted-foreground">
-									<Trans>target[,protocol[,port[,interval]]]</Trans>
+									<Trans>target[,protocol[,port[,interval[,server]]]]</Trans>
 								</p>
 							</div>
 						</div>
@@ -591,6 +604,7 @@ function MonitorDialogContent({
 	const [protocol, setProtocol] = useState<MonitorProtocol>(monitor?.protocol ?? "icmp")
 	const [target, setTarget] = useState(monitor?.target ?? "")
 	const [port, setPort] = useState(monitor?.protocol === "tcp" && monitor.port ? String(monitor.port) : "")
+	const [server, setServer] = useState(monitor?.protocol === "dns" ? (monitor.server ?? "") : "")
 	const [monitorInterval, setMonitorInterval] = useState(String(monitor?.interval ?? defaultInterval))
 	const [loading, setLoading] = useState(false)
 	const [selectedSystemId, setSelectedSystemId] = useState(monitor?.system ?? "")
@@ -609,6 +623,7 @@ function MonitorDialogContent({
 		setProtocol(monitor?.protocol ?? "icmp")
 		setTarget(monitor?.target ?? "")
 		setPort(monitor?.protocol === "tcp" && monitor.port ? String(monitor.port) : "")
+		setServer(monitor?.protocol === "dns" ? (monitor.server ?? "") : "")
 		setMonitorInterval(String(monitor?.interval ?? defaultInterval))
 		setSelectedSystemId(monitor?.system ?? "")
 		setSelectedSystemIds(new Set())
@@ -629,6 +644,7 @@ function MonitorDialogContent({
 					target,
 					protocol,
 					port: protocol === "tcp" ? Number(port) : 0,
+					server: protocol === "dns" ? server.trim() : "",
 					interval: monitorInterval,
 				},
 				monitor ? monitor.enabled : true
@@ -709,7 +725,7 @@ function MonitorDialogContent({
 					<Input
 						value={target}
 						onChange={(e) => setTarget(e.target.value)}
-						placeholder={protocol === "http" ? "http://localhost:8090" : "1.1.1.1"}
+						placeholder={protocol === "http" ? "http://localhost:8090" : protocol === "dns" ? "example.com" : "1.1.1.1"}
 						required
 					/>
 				</div>
@@ -745,6 +761,21 @@ function MonitorDialogContent({
 						/>
 					</div>
 				)}
+				{protocol === "dns" && (
+					<div className="grid gap-2">
+						<Label>
+							<Trans>DNS Server</Trans>
+						</Label>
+						<Input
+							value={server}
+							onChange={(e) => setServer(e.target.value)}
+							placeholder="1.1.1.1"
+						/>
+						<p className="text-xs text-muted-foreground">
+							<Trans>Optional. Defaults to the agent's system resolver.</Trans>
+						</p>
+					</div>
+				)}
 				<div className="grid gap-2">
 					<Label>
 						<Trans>Interval (seconds)</Trans>

internal/site/src/components/network-monitors-table/network-monitors-table.tsx

@@ -47,6 +47,7 @@ import {
 	ArrowUpIcon,
 	EthernetPortIcon,
 	EyeIcon,
+	GlobeIcon,
 	LandmarkIcon,
 	LoaderCircleIcon,
 	ServerIcon,
@@ -720,6 +721,13 @@ function NetworkMonitorSheetContent({
 								<span>{monitor.port}</span>
 							</>
 						)}
+						{monitor.protocol === "dns" && monitor.server && (
+							<>
+								<Separator orientation="vertical" className="h-2.5 bg-muted-foreground opacity-70" />
+								<GlobeIcon className="size-3.5 text-muted-foreground" />
+								<span>{monitor.server}</span>
+							</>
+						)}
 						{monitor.certInfo?.expires ? <CertExpiry cert={monitor.certInfo} /> : null}
 					</SheetDescription>
 				</SheetHeader>

internal/site/src/lib/use-network-monitors.ts

@@ -74,7 +74,7 @@ async function fetchMonitorStats(
 }
 
 const NETWORK_MONITOR_FIELDS =
-	"id,system,target,protocol,port,interval,res,resMin1h,resMax1h,resAvg1h,loss1h,enabled,certInfo,updated"
+	"id,system,target,protocol,port,server,interval,res,resMin1h,resMax1h,resAvg1h,loss1h,enabled,certInfo,updated"
 
 interface UseNetworkMonitorsProps {
 	systemId?: string

internal/site/src/types.d.ts

@@ -644,6 +644,7 @@ export interface NetworkMonitorRecord {
 	target: string
 	protocol: "icmp" | "tcp" | "http" | "dns"
 	port: number
+	server: string
 	res: number
 	resMin1h: number
 	resMax1h: number