vmalert: support $externalLabels and $externalURL in templates

https://github.com/VictoriaMetrics/VictoriaMetrics/issues/2193
Signed-off-by: hagen1778 <roman@victoriametrics.com>

app/vmalert/config/testdata/rules2-good.rules

@@ -25,6 +25,7 @@ groups:
           dynamic: '{{ $x := query "up" | first | value }}{{ if eq 1.0 $x }}one{{ else }}unknown{{ end }}'
         annotations:
           description: Job {{ $labels.job }} is up!
+          external: cluster-{{ $externalLabels.cluster }}; replica-{{ $externalLabels.replica }}
           summary: All instances up {{ range query "up" }}
             {{ . | label "instance" }}
             {{ end }}

app/vmalert/main.go

@@ -167,7 +167,20 @@ func newManager(ctx context.Context) (*manager, error) {
 	if err != nil {
 		return nil, fmt.Errorf("failed to init datasource: %w", err)
 	}
-	nts, err := notifier.Init(alertURLGeneratorFn)
+
+	labels := make(map[string]string, 0)
+	for _, s := range *externalLabels {
+		if len(s) == 0 {
+			continue
+		}
+		n := strings.IndexByte(s, '=')
+		if n < 0 {
+			return nil, fmt.Errorf("missing '=' in `-label`. It must contain label in the form `Name=value`; got %q", s)
+		}
+		labels[s[:n]] = s[n+1:]
+	}
+
+	nts, err := notifier.Init(alertURLGeneratorFn, labels, *externalURL)
 	if err != nil {
 		return nil, fmt.Errorf("failed to init notifier: %w", err)
 	}
@@ -175,7 +188,7 @@ func newManager(ctx context.Context) (*manager, error) {
 		groups:         make(map[uint64]*Group),
 		querierBuilder: q,
 		notifiers:      nts,
-		labels:         map[string]string{},
+		labels:         labels,
 	}
 	rw, err := remotewrite.Init(ctx)
 	if err != nil {
@@ -189,16 +202,6 @@ func newManager(ctx context.Context) (*manager, error) {
 	}
 	manager.rr = rr
 
-	for _, s := range *externalLabels {
-		if len(s) == 0 {
-			continue
-		}
-		n := strings.IndexByte(s, '=')
-		if n < 0 {
-			return nil, fmt.Errorf("missing '=' in `-label`. It must contain label in the form `Name=value`; got %q", s)
-		}
-		manager.labels[s[:n]] = s[n+1:]
-	}
 	return manager, nil
 }
 

app/vmalert/notifier/alert.go

@@ -70,7 +70,13 @@ type AlertTplData struct {
 	Expr   string
 }
 
-const tplHeader = `{{ $value := .Value }}{{ $labels := .Labels }}{{ $expr := .Expr }}`
+var tplHeaders = []string{
+	"{{ $value := .Value }}",
+	"{{ $labels := .Labels }}",
+	"{{ $expr := .Expr }}",
+	"{{ $externalLabels := .ExternalLabels }}",
+	"{{ $externalURL := .ExternalURL }}",
+}
 
 // ExecTemplate executes the Alert template for given
 // map of annotations.
@@ -100,13 +106,15 @@ func templateAnnotations(annotations map[string]string, data AlertTplData, funcs
 	var buf bytes.Buffer
 	eg := new(utils.ErrGroup)
 	r := make(map[string]string, len(annotations))
+	tData := tplData{data, externalLabels, externalURL}
+	header := strings.Join(tplHeaders, "")
 	for key, text := range annotations {
 		buf.Reset()
 		builder.Reset()
-		builder.Grow(len(tplHeader) + len(text))
-		builder.WriteString(tplHeader)
+		builder.Grow(len(header) + len(text))
+		builder.WriteString(header)
 		builder.WriteString(text)
-		if err := templateAnnotation(&buf, builder.String(), data, funcs); err != nil {
+		if err := templateAnnotation(&buf, builder.String(), tData, funcs); err != nil {
 			r[key] = text
 			eg.Add(fmt.Errorf("key %q, template %q: %w", key, text, err))
 			continue
@@ -116,7 +124,13 @@ func templateAnnotations(annotations map[string]string, data AlertTplData, funcs
 	return r, eg.Err()
 }
 
-func templateAnnotation(dst io.Writer, text string, data AlertTplData, funcs template.FuncMap) error {
+type tplData struct {
+	AlertTplData
+	ExternalLabels map[string]string
+	ExternalURL    string
+}
+
+func templateAnnotation(dst io.Writer, text string, data tplData, funcs template.FuncMap) error {
 	t := template.New("").Funcs(funcs).Option("missingkey=zero")
 	tpl, err := t.Parse(text)
 	if err != nil {

app/vmalert/notifier/alert_test.go

@@ -1,12 +1,24 @@
 package notifier
 
 import (
+	"fmt"
 	"testing"
 
 	"github.com/VictoriaMetrics/VictoriaMetrics/app/vmalert/datasource"
 )
 
 func TestAlert_ExecTemplate(t *testing.T) {
+	extLabels := make(map[string]string, 0)
+	const (
+		extCluster = "prod"
+		extDC      = "east"
+		extURL     = "https://foo.bar"
+	)
+	extLabels["cluster"] = extCluster
+	extLabels["dc"] = extDC
+	_, err := Init(nil, extLabels, extURL)
+	checkErr(t, err)
+
 	testCases := []struct {
 		name        string
 		alert       *Alert
@@ -74,6 +86,26 @@ func TestAlert_ExecTemplate(t *testing.T) {
 				"desc":    "bar 1;garply 2;",
 			},
 		},
+		{
+			name: "external",
+			alert: &Alert{
+				Value: 1e4,
+				Labels: map[string]string{
+					"job":      "staging",
+					"instance": "localhost",
+				},
+			},
+			annotations: map[string]string{
+				"url":         "{{ $externalURL }}",
+				"summary":     "Issues with {{$labels.instance}} (dc-{{$externalLabels.dc}}) for job {{$labels.job}}",
+				"description": "It is {{ $value }} connections for {{$labels.instance}} (cluster-{{$externalLabels.cluster}})",
+			},
+			expTpl: map[string]string{
+				"url":         extURL,
+				"summary":     fmt.Sprintf("Issues with localhost (dc-%s) for job staging", extDC),
+				"description": fmt.Sprintf("It is 10000 connections for localhost (cluster-%s)", extCluster),
+			},
+		},
 	}
 
 	qFn := func(q string) ([]datasource.Metric, error) {

app/vmalert/notifier/init.go

@@ -46,13 +46,29 @@ func Reload() error {
 
 var staticNotifiersFn func() []Notifier
 
+var (
+	// externalLabels is a global variable for holding external labels configured via flags
+	// It is supposed to be inited via Init function only.
+	externalLabels map[string]string
+	// externalURL is a global variable for holding external URL value configured via flag
+	// It is supposed to be inited via Init function only.
+	externalURL string
+)
+
 // Init returns a function for retrieving actual list of Notifier objects.
 // Init works in two mods:
 //   * configuration via flags (for backward compatibility). Is always static
 //     and don't support live reloads.
 //   * configuration via file. Supports live reloads and service discovery.
 // Init returns an error if both mods are used.
-func Init(gen AlertURLGenerator) (func() []Notifier, error) {
+func Init(gen AlertURLGenerator, extLabels map[string]string, extURL string) (func() []Notifier, error) {
+	if externalLabels != nil || externalURL != "" {
+		return nil, fmt.Errorf("BUG: notifier.Init was called multiple times")
+	}
+
+	externalURL = extURL
+	externalLabels = extLabels
+
 	if *configPath == "" && len(*addrs) == 0 {
 		return nil, nil
 	}