feature/featuretags: make usermetrics modular

Saves ~102 KB from the min build.

Updates #12614

Change-Id: Ie1d4f439321267b9f98046593cb289ee3c4d6249
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>

cmd/k8s-operator/depaware.txt

@@ -742,7 +742,7 @@ tailscale.com/cmd/k8s-operator dependencies: (generated by github.com/tailscale/
         tailscale.com/logpolicy                                      from tailscale.com/ipn/ipnlocal+
         tailscale.com/logtail                                        from tailscale.com/control/controlclient+
         tailscale.com/logtail/filch                                  from tailscale.com/log/sockstatlog+
-        tailscale.com/metrics                                        from tailscale.com/net/tstun+
+        tailscale.com/metrics                                        from tailscale.com/tsweb+
         tailscale.com/net/bakedroots                                 from tailscale.com/net/tlsdial+
      💣 tailscale.com/net/batching                                   from tailscale.com/wgengine/magicsock
         tailscale.com/net/captivedetection                           from tailscale.com/ipn/ipnlocal+

cmd/tailscaled/debug.go

@@ -28,7 +28,9 @@ import (
 	"tailscale.com/ipn"
 	"tailscale.com/net/netmon"
 	"tailscale.com/tailcfg"
+	"tailscale.com/tsweb/varz"
 	"tailscale.com/types/key"
+	"tailscale.com/util/clientmetric"
 	"tailscale.com/util/eventbus"
 )
 
@@ -58,6 +60,12 @@ func newDebugMux() *http.ServeMux {
 	return mux
 }
 
+func servePrometheusMetrics(w http.ResponseWriter, r *http.Request) {
+	w.Header().Set("Content-Type", "text/plain")
+	varz.Handler(w, r)
+	clientmetric.WritePrometheusExpositionFormat(w)
+}
+
 func debugMode(args []string) error {
 	fs := flag.NewFlagSet("debug", flag.ExitOnError)
 	fs.BoolVar(&debugArgs.ifconfig, "ifconfig", false, "If true, print network interface state")

cmd/tailscaled/depaware-min.txt

@@ -76,7 +76,6 @@ tailscale.com/cmd/tailscaled dependencies: (generated by github.com/tailscale/de
         tailscale.com/logpolicy                                      from tailscale.com/cmd/tailscaled+
         tailscale.com/logtail                                        from tailscale.com/cmd/tailscaled+
         tailscale.com/logtail/filch                                  from tailscale.com/log/sockstatlog+
-        tailscale.com/metrics                                        from tailscale.com/net/tstun+
         tailscale.com/net/bakedroots                                 from tailscale.com/net/tlsdial
      💣 tailscale.com/net/batching                                   from tailscale.com/wgengine/magicsock
         tailscale.com/net/connstats                                  from tailscale.com/net/tstun+
@@ -123,7 +122,6 @@ tailscale.com/cmd/tailscaled dependencies: (generated by github.com/tailscale/de
         tailscale.com/tstime                                         from tailscale.com/control/controlclient+
         tailscale.com/tstime/mono                                    from tailscale.com/net/tstun+
         tailscale.com/tstime/rate                                    from tailscale.com/wgengine/filter
-        tailscale.com/tsweb/varz                                     from tailscale.com/cmd/tailscaled+
         tailscale.com/types/appctype                                 from tailscale.com/ipn/ipnlocal+
         tailscale.com/types/dnstype                                  from tailscale.com/client/tailscale/apitype+
         tailscale.com/types/empty                                    from tailscale.com/ipn+
@@ -150,7 +148,6 @@ tailscale.com/cmd/tailscaled dependencies: (generated by github.com/tailscale/de
         tailscale.com/util/cloudenv                                  from tailscale.com/hostinfo+
         tailscale.com/util/ctxkey                                    from tailscale.com/client/tailscale/apitype+
      💣 tailscale.com/util/deephash                                  from tailscale.com/ipn/ipnlocal+
-     💣 tailscale.com/util/dirwalk                                   from tailscale.com/metrics
         tailscale.com/util/dnsname                                   from tailscale.com/appc+
         tailscale.com/util/eventbus                                  from tailscale.com/control/controlclient+
         tailscale.com/util/execqueue                                 from tailscale.com/appc+
@@ -205,7 +202,7 @@ tailscale.com/cmd/tailscaled dependencies: (generated by github.com/tailscale/de
         golang.org/x/crypto/nacl/secretbox                           from golang.org/x/crypto/nacl/box
         golang.org/x/crypto/poly1305                                 from github.com/tailscale/wireguard-go/device
         golang.org/x/crypto/salsa20/salsa                            from golang.org/x/crypto/nacl/box+
-        golang.org/x/exp/constraints                                 from tailscale.com/tsweb/varz+
+        golang.org/x/exp/constraints                                 from tailscale.com/util/set
         golang.org/x/exp/maps                                        from tailscale.com/ipn/store/mem
         golang.org/x/net/bpf                                         from github.com/mdlayher/genetlink+
         golang.org/x/net/dns/dnsmessage                              from tailscale.com/ipn/ipnlocal+
@@ -321,7 +318,7 @@ tailscale.com/cmd/tailscaled dependencies: (generated by github.com/tailscale/de
         encoding/json                                                from expvar+
         encoding/pem                                                 from crypto/tls+
         errors                                                       from bufio+
-        expvar                                                       from tailscale.com/metrics+
+        expvar                                                       from tailscale.com/wgengine/magicsock
         flag                                                         from tailscale.com/cmd/tailscaled+
         fmt                                                          from compress/flate+
         hash                                                         from crypto+

cmd/tailscaled/depaware-minbox.txt

@@ -99,7 +99,6 @@ tailscale.com/cmd/tailscaled dependencies: (generated by github.com/tailscale/de
         tailscale.com/logpolicy                                      from tailscale.com/cmd/tailscaled+
         tailscale.com/logtail                                        from tailscale.com/cmd/tailscaled+
         tailscale.com/logtail/filch                                  from tailscale.com/log/sockstatlog+
-        tailscale.com/metrics                                        from tailscale.com/net/tstun+
         tailscale.com/net/ace                                        from tailscale.com/cmd/tailscale/cli
         tailscale.com/net/bakedroots                                 from tailscale.com/net/tlsdial
      💣 tailscale.com/net/batching                                   from tailscale.com/wgengine/magicsock
@@ -149,7 +148,6 @@ tailscale.com/cmd/tailscaled dependencies: (generated by github.com/tailscale/de
         tailscale.com/tstime                                         from tailscale.com/control/controlclient+
         tailscale.com/tstime/mono                                    from tailscale.com/net/tstun+
         tailscale.com/tstime/rate                                    from tailscale.com/wgengine/filter
-        tailscale.com/tsweb/varz                                     from tailscale.com/cmd/tailscaled+
         tailscale.com/types/appctype                                 from tailscale.com/ipn/ipnlocal+
         tailscale.com/types/dnstype                                  from tailscale.com/client/tailscale/apitype+
         tailscale.com/types/empty                                    from tailscale.com/ipn+
@@ -177,7 +175,6 @@ tailscale.com/cmd/tailscaled dependencies: (generated by github.com/tailscale/de
         tailscale.com/util/cmpver                                    from tailscale.com/clientupdate
         tailscale.com/util/ctxkey                                    from tailscale.com/client/tailscale/apitype+
      💣 tailscale.com/util/deephash                                  from tailscale.com/ipn/ipnlocal+
-     💣 tailscale.com/util/dirwalk                                   from tailscale.com/metrics
         tailscale.com/util/dnsname                                   from tailscale.com/appc+
         tailscale.com/util/eventbus                                  from tailscale.com/client/local+
         tailscale.com/util/execqueue                                 from tailscale.com/appc+
@@ -233,7 +230,7 @@ tailscale.com/cmd/tailscaled dependencies: (generated by github.com/tailscale/de
         golang.org/x/crypto/nacl/secretbox                           from golang.org/x/crypto/nacl/box
         golang.org/x/crypto/poly1305                                 from github.com/tailscale/wireguard-go/device
         golang.org/x/crypto/salsa20/salsa                            from golang.org/x/crypto/nacl/box+
-        golang.org/x/exp/constraints                                 from tailscale.com/tsweb/varz+
+        golang.org/x/exp/constraints                                 from tailscale.com/util/set
         golang.org/x/exp/maps                                        from tailscale.com/ipn/store/mem
         golang.org/x/net/bpf                                         from github.com/mdlayher/genetlink+
         golang.org/x/net/dns/dnsmessage                              from tailscale.com/cmd/tailscale/cli+
@@ -351,7 +348,7 @@ tailscale.com/cmd/tailscaled dependencies: (generated by github.com/tailscale/de
         encoding/json                                                from expvar+
         encoding/pem                                                 from crypto/tls+
         errors                                                       from bufio+
-        expvar                                                       from tailscale.com/metrics+
+        expvar                                                       from tailscale.com/wgengine/magicsock
         flag                                                         from tailscale.com/cmd/tailscaled+
         fmt                                                          from compress/flate+
         hash                                                         from crypto+

cmd/tailscaled/depaware.txt

@@ -323,7 +323,7 @@ tailscale.com/cmd/tailscaled dependencies: (generated by github.com/tailscale/de
         tailscale.com/logpolicy                                      from tailscale.com/cmd/tailscaled+
         tailscale.com/logtail                                        from tailscale.com/cmd/tailscaled+
         tailscale.com/logtail/filch                                  from tailscale.com/log/sockstatlog+
-        tailscale.com/metrics                                        from tailscale.com/net/tstun+
+        tailscale.com/metrics                                        from tailscale.com/tsweb+
         tailscale.com/net/ace                                        from tailscale.com/feature/ace
         tailscale.com/net/bakedroots                                 from tailscale.com/net/tlsdial+
      💣 tailscale.com/net/batching                                   from tailscale.com/wgengine/magicsock+

cmd/tailscaled/deps_test.go

@@ -265,6 +265,9 @@ func TestMinTailscaledWithCLI(t *testing.T) {
 		"hujson",
 		"pprof",
 		"multierr", // https://github.com/tailscale/tailscale/pull/17379
+		"tailscale.com/metrics",
+		"tailscale.com/tsweb/varz",
+		"dirwalk",
 	}
 	deptest.DepChecker{
 		GOOS:   "linux",

cmd/tailscaled/tailscaled.go

@@ -51,11 +51,9 @@ import (
 	"tailscale.com/safesocket"
 	"tailscale.com/syncs"
 	"tailscale.com/tsd"
-	"tailscale.com/tsweb/varz"
 	"tailscale.com/types/flagtype"
 	"tailscale.com/types/logger"
 	"tailscale.com/types/logid"
-	"tailscale.com/util/clientmetric"
 	"tailscale.com/util/osshare"
 	"tailscale.com/util/syspolicy/pkey"
 	"tailscale.com/util/syspolicy/policyclient"
@@ -831,12 +829,6 @@ func tryEngine(logf logger.Logf, sys *tsd.System, name string) (onlyNetstack boo
 
 var hookNewDebugMux feature.Hook[func() *http.ServeMux]
 
-func servePrometheusMetrics(w http.ResponseWriter, r *http.Request) {
-	w.Header().Set("Content-Type", "text/plain")
-	varz.Handler(w, r)
-	clientmetric.WritePrometheusExpositionFormat(w)
-}
-
 func runDebugServer(logf logger.Logf, mux *http.ServeMux, addr string) {
 	if !buildfeatures.HasDebug {
 		return

cmd/tsidp/depaware.txt

@@ -170,7 +170,7 @@ tailscale.com/cmd/tsidp dependencies: (generated by github.com/tailscale/depawar
         tailscale.com/logpolicy                                      from tailscale.com/ipn/ipnlocal+
         tailscale.com/logtail                                        from tailscale.com/control/controlclient+
         tailscale.com/logtail/filch                                  from tailscale.com/log/sockstatlog+
-        tailscale.com/metrics                                        from tailscale.com/net/tstun+
+        tailscale.com/metrics                                        from tailscale.com/tsweb+
         tailscale.com/net/bakedroots                                 from tailscale.com/ipn/ipnlocal+
      💣 tailscale.com/net/batching                                   from tailscale.com/wgengine/magicsock
         tailscale.com/net/captivedetection                           from tailscale.com/ipn/ipnlocal+

feature/buildfeatures/feature_usermetrics_disabled.go

@@ -0,0 +1,13 @@
+// Copyright (c) Tailscale Inc & AUTHORS
+// SPDX-License-Identifier: BSD-3-Clause
+
+// Code generated by gen.go; DO NOT EDIT.
+
+//go:build ts_omit_usermetrics
+
+package buildfeatures
+
+// HasUserMetrics is whether the binary was built with support for modular feature "Usermetrics (documented, stable) metrics support".
+// Specifically, it's whether the binary was NOT built with the "ts_omit_usermetrics" build tag.
+// It's a const so it can be used for dead code elimination.
+const HasUserMetrics = false

feature/buildfeatures/feature_usermetrics_enabled.go

@@ -0,0 +1,13 @@
+// Copyright (c) Tailscale Inc & AUTHORS
+// SPDX-License-Identifier: BSD-3-Clause
+
+// Code generated by gen.go; DO NOT EDIT.
+
+//go:build !ts_omit_usermetrics
+
+package buildfeatures
+
+// HasUserMetrics is whether the binary was built with support for modular feature "Usermetrics (documented, stable) metrics support".
+// Specifically, it's whether the binary was NOT built with the "ts_omit_usermetrics" build tag.
+// It's a const so it can be used for dead code elimination.
+const HasUserMetrics = true

feature/featuretags/featuretags.go

@@ -270,6 +270,10 @@ var Features = map[FeatureTag]FeatureMeta{
 		Sym:  "UseProxy",
 		Desc: "Support using system proxies as specified by env vars or the system configuration to reach Tailscale servers.",
 	},
+	"usermetrics": {
+		Sym:  "UserMetrics",
+		Desc: "Usermetrics (documented, stable) metrics support",
+	},
 	"wakeonlan": {Sym: "WakeOnLAN", Desc: "Wake-on-LAN support"},
 	"webclient": {
 		Sym: "WebClient", Desc: "Web client support",

ipn/localapi/localapi.go

@@ -99,7 +99,6 @@ var handler = map[string]LocalAPIHandler{
 	"status":                       (*Handler).serveStatus,
 	"update/check":                 (*Handler).serveUpdateCheck,
 	"upload-client-metrics":        (*Handler).serveUploadClientMetrics,
-	"usermetrics":                  (*Handler).serveUserMetrics,
 	"watch-ipn-bus":                (*Handler).serveWatchIPNBus,
 	"whois":                        (*Handler).serveWhoIs,
 }
@@ -126,6 +125,9 @@ func init() {
 		Register("dns-osconfig", (*Handler).serveDNSOSConfig)
 		Register("dns-query", (*Handler).serveDNSQuery)
 	}
+	if buildfeatures.HasUserMetrics {
+		Register("usermetrics", (*Handler).serveUserMetrics)
+	}
 }
 
 // Register registers a new LocalAPI handler for the given name.

net/tstun/wrap.go

@@ -24,7 +24,6 @@ import (
 	"go4.org/mem"
 	"tailscale.com/disco"
 	"tailscale.com/feature/buildfeatures"
-	tsmetrics "tailscale.com/metrics"
 	"tailscale.com/net/connstats"
 	"tailscale.com/net/packet"
 	"tailscale.com/net/packet/checksum"
@@ -213,8 +212,8 @@ type Wrapper struct {
 }
 
 type metrics struct {
-	inboundDroppedPacketsTotal  *tsmetrics.MultiLabelMap[usermetric.DropLabels]
-	outboundDroppedPacketsTotal *tsmetrics.MultiLabelMap[usermetric.DropLabels]
+	inboundDroppedPacketsTotal  *usermetric.MultiLabelMap[usermetric.DropLabels]
+	outboundDroppedPacketsTotal *usermetric.MultiLabelMap[usermetric.DropLabels]
 }
 
 func registerMetrics(reg *usermetric.Registry) *metrics {

tsnet/depaware.txt

@@ -166,7 +166,7 @@ tailscale.com/tsnet dependencies: (generated by github.com/tailscale/depaware)
         tailscale.com/logpolicy                                      from tailscale.com/ipn/ipnlocal+
         tailscale.com/logtail                                        from tailscale.com/control/controlclient+
         tailscale.com/logtail/filch                                  from tailscale.com/log/sockstatlog+
-        tailscale.com/metrics                                        from tailscale.com/net/tstun+
+        tailscale.com/metrics                                        from tailscale.com/tsweb+
         tailscale.com/net/bakedroots                                 from tailscale.com/ipn/ipnlocal+
      💣 tailscale.com/net/batching                                   from tailscale.com/wgengine/magicsock
         tailscale.com/net/captivedetection                           from tailscale.com/ipn/ipnlocal+

util/usermetric/metrics.go

@@ -10,15 +10,15 @@ package usermetric
 import (
 	"sync"
 
-	"tailscale.com/metrics"
+	"tailscale.com/feature/buildfeatures"
 )
 
 // Metrics contains user-facing metrics that are used by multiple packages.
 type Metrics struct {
 	initOnce sync.Once
 
-	droppedPacketsInbound  *metrics.MultiLabelMap[DropLabels]
-	droppedPacketsOutbound *metrics.MultiLabelMap[DropLabels]
+	droppedPacketsInbound  *MultiLabelMap[DropLabels]
+	droppedPacketsOutbound *MultiLabelMap[DropLabels]
 }
 
 // DropReason is the reason why a packet was dropped.
@@ -55,6 +55,9 @@ type DropLabels struct {
 
 // initOnce initializes the common metrics.
 func (r *Registry) initOnce() {
+	if !buildfeatures.HasUserMetrics {
+		return
+	}
 	r.m.initOnce.Do(func() {
 		r.m.droppedPacketsInbound = NewMultiLabelMapWithRegistry[DropLabels](
 			r,
@@ -73,13 +76,13 @@ func (r *Registry) initOnce() {
 
 // DroppedPacketsOutbound returns the outbound dropped packet metric, creating it
 // if necessary.
-func (r *Registry) DroppedPacketsOutbound() *metrics.MultiLabelMap[DropLabels] {
+func (r *Registry) DroppedPacketsOutbound() *MultiLabelMap[DropLabels] {
 	r.initOnce()
 	return r.m.droppedPacketsOutbound
 }
 
 // DroppedPacketsInbound returns the inbound dropped packet metric.
-func (r *Registry) DroppedPacketsInbound() *metrics.MultiLabelMap[DropLabels] {
+func (r *Registry) DroppedPacketsInbound() *MultiLabelMap[DropLabels] {
 	r.initOnce()
 	return r.m.droppedPacketsInbound
 }

util/usermetric/omit.go

@@ -0,0 +1,29 @@
+// Copyright (c) Tailscale Inc & AUTHORS
+// SPDX-License-Identifier: BSD-3-Clause
+
+//go:build ts_omit_usermetrics
+
+package usermetric
+
+type Registry struct {
+	m Metrics
+}
+
+func (*Registry) NewGauge(name, help string) *Gauge { return nil }
+
+type MultiLabelMap[T comparable] = noopMap[T]
+
+type noopMap[T comparable] struct{}
+
+type Gauge struct{}
+
+func (*Gauge) Set(float64) {}
+
+func NewMultiLabelMapWithRegistry[T comparable](m *Registry, name string, promType, helpText string) *MultiLabelMap[T] {
+	return nil
+}
+
+func (*noopMap[T]) Add(T, int64) {}
+func (*noopMap[T]) Set(T, any)   {}
+
+func (r *Registry) Handler(any, any) {} // no-op HTTP handler

util/usermetric/usermetric.go

@@ -1,6 +1,8 @@
 // Copyright (c) Tailscale Inc & AUTHORS
 // SPDX-License-Identifier: BSD-3-Clause
 
+//go:build !ts_omit_usermetrics
+
 // Package usermetric provides a container and handler
 // for user-facing metrics.
 package usermetric
@@ -25,6 +27,10 @@ type Registry struct {
 	m Metrics
 }
 
+// MultiLabelMap is an alias for metrics.MultiLabelMap in the common case,
+// or an alias to a lighter type when usermetrics are omitted from the build.
+type MultiLabelMap[T comparable] = metrics.MultiLabelMap[T]
+
 // NewMultiLabelMapWithRegistry creates and register a new
 // MultiLabelMap[T] variable with the given name and returns it.
 // The variable is registered with the userfacing metrics package.