Add externalURL template function (#2716)

This allows users to e.g. add links back to the generating Prometheus
right in their alert templates.

rules/alerting.go

@@ -15,6 +15,7 @@ package rules
 
 import (
 	"fmt"
+	"net/url"
 	"sync"
 	"time"
 
@@ -148,7 +149,7 @@ const resolvedRetention = 15 * time.Minute
 
 // Eval evaluates the rule expression and then creates pending alerts and fires
 // or removes previously pending alerts accordingly.
-func (r *AlertingRule) Eval(ctx context.Context, ts model.Time, engine *promql.Engine, externalURLPath string) (model.Vector, error) {
+func (r *AlertingRule) Eval(ctx context.Context, ts model.Time, engine *promql.Engine, externalURL *url.URL) (model.Vector, error) {
 	query, err := engine.NewInstantQuery(r.vector.String(), ts)
 	if err != nil {
 		return nil, err
@@ -191,7 +192,7 @@ func (r *AlertingRule) Eval(ctx context.Context, ts model.Time, engine *promql.E
 				tmplData,
 				ts,
 				engine,
-				externalURLPath,
+				externalURL,
 			)
 			result, err := tmpl.Expand()
 			if err != nil {

rules/manager.go

@@ -113,7 +113,7 @@ const (
 type Rule interface {
 	Name() string
 	// eval evaluates the rule, including any associated recording or alerting actions.
-	Eval(context.Context, model.Time, *promql.Engine, string) (model.Vector, error)
+	Eval(context.Context, model.Time, *promql.Engine, *url.URL) (model.Vector, error)
 	// String returns a human-readable string representation of the rule.
 	String() string
 	// HTMLSnippet returns a human-readable string representation of the rule,
@@ -274,7 +274,7 @@ func (g *Group) Eval() {
 
 			evalTotal.WithLabelValues(rtyp).Inc()
 
-			vector, err := rule.Eval(g.opts.Context, now, g.opts.QueryEngine, g.opts.ExternalURL.Path)
+			vector, err := rule.Eval(g.opts.Context, now, g.opts.QueryEngine, g.opts.ExternalURL)
 			if err != nil {
 				// Canceled queries are intentional termination of queries. This normally
 				// happens on shutdown and thus we skip logging of any errors here.

rules/manager_test.go

@@ -105,7 +105,7 @@ func TestAlertingRule(t *testing.T) {
 	for i, test := range tests {
 		evalTime := model.Time(0).Add(test.time)
 
-		res, err := rule.Eval(suite.Context(), evalTime, suite.QueryEngine(), "")
+		res, err := rule.Eval(suite.Context(), evalTime, suite.QueryEngine(), nil)
 		if err != nil {
 			t.Fatalf("Error during alerting rule evaluation: %s", err)
 		}

rules/recording.go

@@ -16,6 +16,7 @@ package rules
 import (
 	"fmt"
 	"html/template"
+	"net/url"
 
 	"github.com/prometheus/common/model"
 	"golang.org/x/net/context"
@@ -46,7 +47,7 @@ func (rule RecordingRule) Name() string {
 }
 
 // Eval evaluates the rule and then overrides the metric names and labels accordingly.
-func (rule RecordingRule) Eval(ctx context.Context, timestamp model.Time, engine *promql.Engine, _ string) (model.Vector, error) {
+func (rule RecordingRule) Eval(ctx context.Context, timestamp model.Time, engine *promql.Engine, _ *url.URL) (model.Vector, error) {
 	query, err := engine.NewInstantQuery(rule.vector.String(), timestamp)
 	if err != nil {
 		return nil, err

rules/recording_test.go

@@ -63,7 +63,7 @@ func TestRuleEval(t *testing.T) {
 
 	for _, test := range suite {
 		rule := NewRecordingRule(test.name, test.expr, test.labels)
-		result, err := rule.Eval(ctx, now, engine, "")
+		result, err := rule.Eval(ctx, now, engine, nil)
 		if err != nil {
 			t.Fatalf("Error evaluating %s", test.name)
 		}

template/template.go

@@ -18,6 +18,7 @@ import (
 	"errors"
 	"fmt"
 	"math"
+	"net/url"
 	"regexp"
 	"sort"
 	"strings"
@@ -111,7 +112,7 @@ type Expander struct {
 }
 
 // NewTemplateExpander returns a template expander ready to use.
-func NewTemplateExpander(ctx context.Context, text string, name string, data interface{}, timestamp model.Time, queryEngine *promql.Engine, pathPrefix string) *Expander {
+func NewTemplateExpander(ctx context.Context, text string, name string, data interface{}, timestamp model.Time, queryEngine *promql.Engine, externalURL *url.URL) *Expander {
 	return &Expander{
 		text: text,
 		name: name,
@@ -247,7 +248,10 @@ func NewTemplateExpander(ctx context.Context, text string, name string, data int
 				return fmt.Sprint(t)
 			},
 			"pathPrefix": func() string {
-				return pathPrefix
+				return externalURL.Path
+			},
+			"externalURL": func() string {
+				return externalURL.String()
 			},
 		},
 	}

template/template_test.go

@@ -15,6 +15,7 @@ package template
 
 import (
 	"math"
+	"net/url"
 	"testing"
 
 	"github.com/prometheus/common/model"
@@ -196,6 +197,16 @@ func TestTemplateExpansion(t *testing.T) {
 			output: "x",
 			html:   true,
 		},
+		{
+			// pathPrefix.
+			text:   "{{ pathPrefix }}",
+			output: "/path/prefix",
+		},
+		{
+			// externalURL.
+			text:   "{{ externalURL }}",
+			output: "http://testhost:9090/path/prefix",
+		},
 	}
 
 	time := model.Time(0)
@@ -218,10 +229,15 @@ func TestTemplateExpansion(t *testing.T) {
 
 	engine := promql.NewEngine(storage, nil)
 
+	extURL, err := url.Parse("http://testhost:9090/path/prefix")
+	if err != nil {
+		panic(err)
+	}
+
 	for i, s := range scenarios {
 		var result string
 		var err error
-		expander := NewTemplateExpander(context.Background(), s.text, "test", s.input, time, engine, "")
+		expander := NewTemplateExpander(context.Background(), s.text, "test", s.input, time, engine, extURL)
 		if s.html {
 			result, err = expander.ExpandHTML(nil)
 		} else {

web/web.go

@@ -326,7 +326,7 @@ func (h *Handler) consoles(w http.ResponseWriter, r *http.Request) {
 		Path:      strings.TrimLeft(name, "/"),
 	}
 
-	tmpl := template.NewTemplateExpander(h.context, string(text), "__console_"+name, data, h.now(), h.queryEngine, h.options.ExternalURL.Path)
+	tmpl := template.NewTemplateExpander(h.context, string(text), "__console_"+name, data, h.now(), h.queryEngine, h.options.ExternalURL)
 	filenames, err := filepath.Glob(h.options.ConsoleLibrariesPath + "/*.lib")
 	if err != nil {
 		http.Error(w, err.Error(), http.StatusInternalServerError)
@@ -521,7 +521,7 @@ func (h *Handler) executeTemplate(w http.ResponseWriter, name string, data inter
 		http.Error(w, err.Error(), http.StatusInternalServerError)
 	}
 
-	tmpl := template.NewTemplateExpander(h.context, text, name, data, h.now(), h.queryEngine, h.options.ExternalURL.Path)
+	tmpl := template.NewTemplateExpander(h.context, text, name, data, h.now(), h.queryEngine, h.options.ExternalURL)
 	tmpl.Funcs(tmplFuncs(h.consolesPath(), h.options))
 
 	result, err := tmpl.ExpandHTML(nil)