Add silence logging option

cmd/alertmanager/main.go

@@ -150,6 +150,7 @@ func run() int {
 		maxSilences         = kingpin.Flag("silences.max-silences", "Maximum number of silences, including expired silences. If negative or zero, no limit is set.").Default("0").Int()
 		maxSilenceSizeBytes = kingpin.Flag("silences.max-silence-size-bytes", "Maximum silence size in bytes. If negative or zero, no limit is set.").Default("0").Int()
 		alertGCInterval     = kingpin.Flag("alerts.gc-interval", "Interval between alert GC.").Default("30m").Duration()
+		silenceLogging      = kingpin.Flag("log.silences", "Enable logging silences. If it is enabled, the status change of silence will be logged").Bool()
 
 		webConfig      = webflag.AddFlags(kingpin.CommandLine, ":9093")
 		externalURL    = kingpin.Flag("web.external-url", "The URL under which Alertmanager is externally reachable (for example, if Alertmanager is served via a reverse proxy). Used for generating relative and absolute links back to Alertmanager itself. If the URL has a path portion, it will be used to prefix all HTTP endpoints served by Alertmanager. If omitted, relevant URL components will be derived automatically.").String()
@@ -299,6 +300,7 @@ func run() int {
 		},
 		Logger:  logger.With("component", "silences"),
 		Metrics: prometheus.DefaultRegisterer,
+		Logging: *silenceLogging,
 	}
 
 	silences, err := silence.New(silenceOpts)

silence/silence.go

@@ -26,6 +26,7 @@ import (
 	"reflect"
 	"regexp"
 	"sort"
+	"strings"
 	"sync"
 	"time"
 
@@ -194,6 +195,7 @@ type Silences struct {
 	metrics   *metrics
 	retention time.Duration
 	limits    Limits
+	logging   bool
 
 	mtx       sync.RWMutex
 	st        state
@@ -331,6 +333,8 @@ type Options struct {
 	Retention time.Duration
 	Limits    Limits
 
+	Logging bool
+
 	// A logger used by background processing.
 	Logger  *slog.Logger
 	Metrics prometheus.Registerer
@@ -355,6 +359,7 @@ func New(o Options) (*Silences, error) {
 		logger:    promslog.NewNopLogger(),
 		retention: o.Retention,
 		limits:    o.Limits,
+		logging:   o.Logging,
 		broadcast: func([]byte) {},
 		st:        state{},
 	}
@@ -616,6 +621,9 @@ func (s *Silences) Set(sil *pb.Silence) error {
 		if err := s.checkSizeLimits(msil); err != nil {
 			return err
 		}
+		if s.logging {
+			s.logginSilences("update silence", sil)
+		}
 		return s.setSilence(msil, now)
 	}
 
@@ -652,6 +660,9 @@ func (s *Silences) Set(sil *pb.Silence) error {
 		}
 	}
 
+	if s.logging {
+		s.logginSilences("create silence", sil)
+	}
 	return s.setSilence(msil, now)
 }
 
@@ -711,6 +722,9 @@ func (s *Silences) expire(id string) error {
 		sil.EndsAt = now
 	}
 	sil.UpdatedAt = now
+	if s.logging {
+		s.logginSilences("expire silence", sil)
+	}
 	return s.setSilence(s.toMeshSilence(sil), now)
 }
 
@@ -1053,3 +1067,35 @@ func openReplace(filename string) (*replaceFile, error) {
 	}
 	return rf, nil
 }
+
+// logging silence status changes.
+//
+// XXX: This rewrites some code present in cli/format/format.go,
+// labelsMatcher() and cli/format/format_extended.go,
+// FormatSilences(). Refactoring this seems a little out of scope for
+// now.
+func (s *Silences) logginSilences(msg string, sil *pb.Silence) {
+	var listMatchers []string
+	matcherTypeOperator := map[string]string{
+		"EQUAL":      "=",
+		"REGEXP":     "=~",
+		"NOT_EQUAL":  "!=",
+		"NOT_REGEXP": "!~",
+	}
+	for _, matcher := range sil.Matchers {
+		ms := []string{matcher.Name, matcherTypeOperator[matcher.Type.String()], matcher.Pattern}
+		m := strings.Join(ms, ``)
+		listMatchers = append(listMatchers, m)
+	}
+	strMatchers := strings.Join(listMatchers, `,`)
+
+	s.logger.Info(
+		msg,
+		"Id", sil.Id,
+		"CreatedBy", sil.CreatedBy,
+		"Comment", sil.Comment,
+		"StartsAt", sil.StartsAt,
+		"EndsAt", sil.EndsAt,
+		"Matchers", strMatchers,
+	)
+}