Merge pull request #1791 from prometheus/fabxc-routepref

web: add -web.route-prefix flag

cmd/prometheus/config.go

@@ -81,6 +81,10 @@ func init() {
 		&cfg.prometheusURL, "web.external-url", "",
 		"The URL under which Prometheus is externally reachable (for example, if Prometheus is served via a reverse proxy). Used for generating relative and absolute links back to Prometheus itself. If the URL has a path portion, it will be used to prefix all HTTP endpoints served by Prometheus. If omitted, relevant URL components will be derived automatically.",
 	)
+	cfg.fs.StringVar(
+		&cfg.web.RoutePrefix, "web.route-prefix", "",
+		"Prefix for the internal routes of web endpoints. Defaults to path of -web.external-url.",
+	)
 	cfg.fs.StringVar(
 		&cfg.web.MetricsPath, "web.telemetry-path", "/metrics",
 		"Path under which to expose metrics.",
@@ -248,6 +252,13 @@ func parse(args []string) error {
 	if err := parsePrometheusURL(); err != nil {
 		return err
 	}
+	// Default -web.route-prefix to path of -web.external-url.
+	if cfg.web.RoutePrefix == "" {
+		cfg.web.RoutePrefix = cfg.web.ExternalURL.Path
+	}
+	// RoutePrefix must always be at least '/'.
+	cfg.web.RoutePrefix = "/" + strings.Trim(cfg.web.RoutePrefix, "/")
+
 	if err := parseInfluxdbURL(); err != nil {
 		return err
 	}

web/web.go

@@ -99,6 +99,7 @@ type PrometheusVersion struct {
 type Options struct {
 	ListenAddress        string
 	ExternalURL          *url.URL
+	RoutePrefix          string
 	MetricsPath          string
 	UseLocalAssets       bool
 	UserAssetsPath       string
@@ -137,12 +138,12 @@ func New(
 		apiV1: api_v1.NewAPI(qe, st),
 	}
 
-	if o.ExternalURL.Path != "" {
+	if o.RoutePrefix != "/" {
 		// If the prefix is missing for the root path, prepend it.
 		router.Get("/", func(w http.ResponseWriter, r *http.Request) {
-			http.Redirect(w, r, o.ExternalURL.Path, http.StatusFound)
+			http.Redirect(w, r, o.RoutePrefix, http.StatusFound)
 		})
-		router = router.WithPrefix(o.ExternalURL.Path)
+		router = router.WithPrefix(o.RoutePrefix)
 	}
 
 	instrh := prometheus.InstrumentHandler