cmd/tailscaled: include Go runtime metrics in /debug/metrics

Fixes #3772

Change-Id: I237ea23268664d99e83d27890146018b04474556
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>

cmd/tailscaled/depaware.txt

@@ -187,7 +187,7 @@ tailscale.com/cmd/tailscaled dependencies: (generated by github.com/tailscale/de
         tailscale.com/logtail                                        from tailscale.com/logpolicy+
         tailscale.com/logtail/backoff                                from tailscale.com/cmd/tailscaled+
         tailscale.com/logtail/filch                                  from tailscale.com/logpolicy
-     💣 tailscale.com/metrics                                        from tailscale.com/derp
+     💣 tailscale.com/metrics                                        from tailscale.com/derp+
         tailscale.com/net/dns                                        from tailscale.com/cmd/tailscaled+
         tailscale.com/net/dns/resolver                               from tailscale.com/net/dns+
         tailscale.com/net/dnscache                                   from tailscale.com/control/controlclient+
@@ -219,6 +219,7 @@ tailscale.com/cmd/tailscaled dependencies: (generated by github.com/tailscale/de
         tailscale.com/tstime                                         from tailscale.com/wgengine/magicsock
      💣 tailscale.com/tstime/mono                                    from tailscale.com/net/tstun+
         tailscale.com/tstime/rate                                    from tailscale.com/wgengine/filter
+        tailscale.com/tsweb                                          from tailscale.com/cmd/tailscaled
         tailscale.com/types/dnstype                                  from tailscale.com/ipn/ipnlocal+
         tailscale.com/types/empty                                    from tailscale.com/control/controlclient+
         tailscale.com/types/flagtype                                 from tailscale.com/cmd/tailscaled

cmd/tailscaled/tailscaled.go

@@ -41,6 +41,7 @@ import (
 	"tailscale.com/net/tstun"
 	"tailscale.com/paths"
 	"tailscale.com/safesocket"
+	"tailscale.com/tsweb"
 	"tailscale.com/types/flagtype"
 	"tailscale.com/types/logger"
 	"tailscale.com/util/clientmetric"
@@ -514,6 +515,7 @@ func newDebugMux() *http.ServeMux {
 
 func servePrometheusMetrics(w http.ResponseWriter, r *http.Request) {
 	w.Header().Set("Content-Type", "text/plain")
+	tsweb.VarzHandler(w, r)
 	clientmetric.WritePrometheusExpositionFormat(w)
 }
 

tstest/integration/tailscaled_deps_test_darwin.go

@@ -30,6 +30,7 @@ import (
 	_ "tailscale.com/paths"
 	_ "tailscale.com/safesocket"
 	_ "tailscale.com/tailcfg"
+	_ "tailscale.com/tsweb"
 	_ "tailscale.com/types/flagtype"
 	_ "tailscale.com/types/key"
 	_ "tailscale.com/types/logger"

tstest/integration/tailscaled_deps_test_freebsd.go

@@ -30,6 +30,7 @@ import (
 	_ "tailscale.com/paths"
 	_ "tailscale.com/safesocket"
 	_ "tailscale.com/tailcfg"
+	_ "tailscale.com/tsweb"
 	_ "tailscale.com/types/flagtype"
 	_ "tailscale.com/types/key"
 	_ "tailscale.com/types/logger"

tstest/integration/tailscaled_deps_test_linux.go

@@ -30,6 +30,7 @@ import (
 	_ "tailscale.com/paths"
 	_ "tailscale.com/safesocket"
 	_ "tailscale.com/tailcfg"
+	_ "tailscale.com/tsweb"
 	_ "tailscale.com/types/flagtype"
 	_ "tailscale.com/types/key"
 	_ "tailscale.com/types/logger"

tstest/integration/tailscaled_deps_test_openbsd.go

@@ -30,6 +30,7 @@ import (
 	_ "tailscale.com/paths"
 	_ "tailscale.com/safesocket"
 	_ "tailscale.com/tailcfg"
+	_ "tailscale.com/tsweb"
 	_ "tailscale.com/types/flagtype"
 	_ "tailscale.com/types/key"
 	_ "tailscale.com/types/logger"

tstest/integration/tailscaled_deps_test_windows.go

@@ -34,6 +34,7 @@ import (
 	_ "tailscale.com/paths"
 	_ "tailscale.com/safesocket"
 	_ "tailscale.com/tailcfg"
+	_ "tailscale.com/tsweb"
 	_ "tailscale.com/types/flagtype"
 	_ "tailscale.com/types/key"
 	_ "tailscale.com/types/logger"