support loading webhook URL from a file

/cc prometheus#2498

Signed-off-by: Simon Rozet <me@simonrozet.com>

config/notifiers.go

@@ -473,7 +473,8 @@ type WebhookConfig struct {
 	HTTPConfig *commoncfg.HTTPClientConfig `yaml:"http_config,omitempty" json:"http_config,omitempty"`
 
 	// URL to send POST request to.
-	URL *URL `yaml:"url" json:"url"`
+	URL     *URL   `yaml:"url" json:"url"`
+	URLFile string `yaml:"url_file" json:"url_file"`
 	// MaxAlerts is the maximum number of alerts to be sent per webhook message.
 	// Alerts exceeding this threshold will be truncated. Setting this to 0
 	// allows an unlimited number of alerts.
@@ -487,8 +488,11 @@ func (c *WebhookConfig) UnmarshalYAML(unmarshal func(interface{}) error) error {
 	if err := unmarshal((*plain)(c)); err != nil {
 		return err
 	}
-	if c.URL == nil {
-		return fmt.Errorf("missing URL in webhook config")
+	if c.URL == nil && c.URLFile == "" {
+		return fmt.Errorf("one of url or url_file must be configured")
+	}
+	if c.URL != nil && c.URLFile != "" {
+		return fmt.Errorf("at most one of url & url_file must be configured")
 	}
 	if c.URL.Scheme != "https" && c.URL.Scheme != "http" {
 		return fmt.Errorf("scheme required for webhook url")

config/notifiers_test.go

@@ -228,7 +228,25 @@ func TestWebhookURLIsPresent(t *testing.T) {
 	var cfg WebhookConfig
 	err := yaml.UnmarshalStrict([]byte(in), &cfg)
 
-	expected := "missing URL in webhook config"
+	expected := "one of url or url_file must be configured"
+
+	if err == nil {
+		t.Fatalf("no error returned, expected:\n%v", expected)
+	}
+	if err.Error() != expected {
+		t.Errorf("\nexpected:\n%v\ngot:\n%v", expected, err.Error())
+	}
+}
+
+func TestWebhookURLOrURLFile(t *testing.T) {
+	in := `
+url: 'http://example.com'
+url_file: 'http://example.com'
+`
+	var cfg WebhookConfig
+	err := yaml.UnmarshalStrict([]byte(in), &cfg)
+
+	expected := "at most one of url & url_file must be configured"
 
 	if err == nil {
 		t.Fatalf("no error returned, expected:\n%v", expected)

docs/configuration.md

@@ -862,7 +862,7 @@ Pushover notifications are sent via the [Pushover API](https://pushover.net/api)
 # Whether to notify about resolved alerts.
 [ send_resolved: <boolean> | default = true ]
 
-# The recipient user's key. 
+# The recipient user's key.
 # user_key and user_key_file are mutually exclusive.
 user_key: <secret>
 user_key_file: <filepath>
@@ -1116,7 +1116,9 @@ The webhook receiver allows configuring a generic receiver.
 [ send_resolved: <boolean> | default = true ]
 
 # The endpoint to send HTTP POST requests to.
+# url and url_file are mutually exclusive.
 url: <string>
+url_file: <filepath>
 
 # The HTTP client's configuration.
 [ http_config: <http_config> | default = global.http_config ]

notify/webhook/webhook.go

@@ -20,6 +20,7 @@ import (
 	"fmt"
 	"io"
 	"net/http"
+	"os"
 
 	"github.com/go-kit/log"
 	"github.com/go-kit/log/level"
@@ -101,7 +102,18 @@ func (n *Notifier) Notify(ctx context.Context, alerts ...*types.Alert) (bool, er
 		return false, err
 	}
 
-	resp, err := notify.PostJSON(ctx, n.client, n.conf.URL.String(), &buf)
+	var url string
+	if n.conf.URL != nil {
+		url = n.conf.URL.String()
+	} else {
+		content, err := os.ReadFile(n.conf.URLFile)
+		if err != nil {
+			return false, fmt.Errorf("read url_file: %w", err)
+		}
+		url = string(content)
+	}
+
+	resp, err := notify.PostJSON(ctx, n.client, url, &buf)
 	if err != nil {
 		return true, err
 	}