Always set presence/up from go tsmon apps.

common/tsmon/metric/standard_metrics.go

 // Copyright 2016 The LUCI Authors. All rights reserved.
 // Use of this source code is governed under the Apache License, Version 2.0
 // that can be found in the LICENSE file.
 
 package metric
 
 import (
         "strings"
         "time"
 
         "golang.org/x/net/context"
 
+        "github.com/luci/luci-go/common/tsmon"
         "github.com/luci/luci-go/common/tsmon/distribution"
         "github.com/luci/luci-go/common/tsmon/field"
         "github.com/luci/luci-go/common/tsmon/types"
 )
 
 // Metrics common to all tasks and devices.
 var (
         presenceMetric = NewBool(
                 "presence/up",
                 "Set to True when the program is running, missing otherwise.",
@@ skipping 71 matching lines @@
         serverResponseStatusMetric = NewCounter(
                 "http/server_response_status",
                 "Number of responses sent by HTTP status code.",
                 types.MetricMetadata{},
                 field.Int("status"),    // HTTP status code
                 field.String("name"),   // URL template
                 field.Bool("is_robot")) // If request is made by a bot
 
 )
 
-// UpdatePresenceMetrics sets the presence/up metric.
-func UpdatePresenceMetrics(ctx context.Context) {
-        presenceMetric.Set(ctx, true)
+func init() {
+        registerCallbacks(context.Background())
+}
+
+func registerCallbacks(ctx context.Context) {
+        tsmon.RegisterCallbackIn(ctx, func(ctx context.Context) {
+                presenceMetric.Set(ctx, true)
+        })
 }
 
 const (
         millisecondsInASecond = 1000.0
 )
 
 // UpdateHTTPMetrics updates the metrics for a request to a remote server.
 func UpdateHTTPMetrics(ctx context.Context, name string, client string,
         code int, duration time.Duration, requestBytes int64, responseBytes int64) {
         requestBytesMetric.Add(ctx, float64(requestBytes), name, client)
         responseBytesMetric.Add(ctx, float64(responseBytes), name, client)
         requestDurationsMetric.Add(ctx, duration.Seconds()*millisecondsInASecond, name, client)
         responseStatusMetric.Add(ctx, 1, code, name, client)
 }
 
 // UpdateServerMetrics updates the metrics for a handled request.
 func UpdateServerMetrics(ctx context.Context, name string, code int,
         duration time.Duration, requestBytes int64, responseBytes int64,
         userAgent string) {
         isRobot := (strings.Contains(userAgent, "GoogleBot") ||
                 strings.Contains(userAgent, "GoogleSecurityScanner") ||
                 userAgent == "B3M/prober")
         serverDurationsMetric.Add(ctx, duration.Seconds()*millisecondsInASecond,
                 code, name, isRobot)
         serverResponseStatusMetric.Add(ctx, 1, code, name, isRobot)
         serverRequestBytesMetric.Add(ctx, float64(requestBytes), code, name, isRobot)
         serverResponseBytesMetric.Add(ctx, float64(responseBytes), code, name, isRobot)
 }