Make loadable templates configurable

config/config.go

@@ -16,6 +16,7 @@ package config
 import (
 	"fmt"
 	"io/ioutil"
+	"path/filepath"
 	"regexp"
 	"strings"
 
@@ -40,7 +41,28 @@ func LoadFile(filename string) (*Config, error) {
 	if err != nil {
 		return nil, err
 	}
-	return Load(string(content))
+	cfg, err := Load(string(content))
+	if err != nil {
+		return nil, err
+	}
+
+	resolveFilepaths(filepath.Dir(filename), cfg)
+	return cfg, nil
+}
+
+// resolveFilepaths joins all relative paths in a configuration
+// with a given base directory.
+func resolveFilepaths(baseDir string, cfg *Config) {
+	join := func(fp string) string {
+		if len(fp) > 0 && !filepath.IsAbs(fp) {
+			fp = filepath.Join(baseDir, fp)
+		}
+		return fp
+	}
+
+	for i, tf := range cfg.Templates {
+		cfg.Templates[i] = join(tf)
+	}
 }
 
 // Config is the top-level configuration for Alertmanager's config files.
@@ -48,6 +70,7 @@ type Config struct {
 	Routes              []*Route              `yaml:"routes,omitempty"`
 	InhibitRules        []*InhibitRule        `yaml:"inhibit_rules,omitempty"`
 	NotificationConfigs []*NotificationConfig `yaml:"notification_configs,omitempty"`
+	Templates           []string              `yaml:"templates"`
 
 	// Catches all undefined fields and must be empty after parsing.
 	XXX map[string]interface{} `yaml:",inline"`

main.go

@@ -22,6 +22,7 @@ import (
 	"os/signal"
 	"path/filepath"
 	"syscall"
+	"text/template"
 
 	"github.com/prometheus/common/log"
 	"github.com/prometheus/common/route"
@@ -153,6 +154,16 @@ func reloadConfig(filename string, rls ...types.Reloadable) error {
 		return err
 	}
 
+	t := template.New("")
+	for _, tpath := range conf.Templates {
+		t, err = t.ParseGlob(tpath)
+		if err != nil {
+			return err
+		}
+	}
+
+	notify.SetTemplate(t)
+
 	for _, rl := range rls {
 		rl.ApplyConfig(conf)
 	}

notify/impl.go

@@ -172,6 +172,6 @@ func (n *Slack) Notify(ctx context.Context, as ...*types.Alert) error {
 
 var tmpl *template.Template
 
-func init() {
-	tmpl = template.Must(template.ParseGlob("templates/*.tmpl"))
+func SetTemplate(t *template.Template) {
+	tmpl = t
 }

types/types.go

@@ -16,6 +16,12 @@ type Reloadable interface {
 	ApplyConfig(*config.Config)
 }
 
+type ReloadFunc func(*config.Config)
+
+func (f ReloadFunc) ApplyConfig(cfg *config.Config) {
+	f(cfg)
+}
+
 // Alert wraps a model.Alert with additional information relevant
 // to internal of the Alertmanager.
 // The type is never exposed to external communication and the