app/vmagent: list user-visible endpoints at http://vmagent:8429/

While at it, use common WriteAPIHelp function for the listing in vmagent, vmalert and victoria-metrics

app/vmagent/main.go

@@ -148,7 +148,15 @@ func requestHandler(w http.ResponseWriter, r *http.Request) bool {
 		if r.Method != "GET" {
 			return false
 		}
-		fmt.Fprintf(w, "vmagent - see docs at https://docs.victoriametrics.com/vmagent.html")
+		fmt.Fprintf(w, "<h2>vmagent</h2>")
+		fmt.Fprintf(w, "See docs at <a href='https://docs.victoriametrics.com/vmagent.html'>https://docs.victoriametrics.com/vmagent.html</a></br>")
+		fmt.Fprintf(w, "Useful endpoints:</br>")
+		httpserver.WriteAPIHelp(w, [][2]string{
+			{"/targets", "discovered targets list"},
+			{"/api/v1/targets", "advanced information about discovered targets in JSON format"},
+			{"/metrics", "available service metrics"},
+			{"/-/reload", "reload configuration"},
+		})
 		return true
 	}
 	path := strings.Replace(r.URL.Path, "//", "/", -1)

app/vmalert/web.go

@@ -17,25 +17,19 @@ type requestHandler struct {
 	m *manager
 }
 
-var pathList = [][]string{
-	{"/api/v1/groups", "list all loaded groups and rules"},
-	{"/api/v1/alerts", "list all active alerts"},
-	{"/api/v1/groupID/alertID/status", "get alert status by ID"},
-	// /metrics is served by httpserver by default
-	{"/metrics", "list of application metrics"},
-	{"/-/reload", "reload configuration"},
-}
-
 func (rh *requestHandler) handler(w http.ResponseWriter, r *http.Request) bool {
 	switch r.URL.Path {
 	case "/":
 		if r.Method != "GET" {
 			return false
 		}
-		for _, path := range pathList {
-			p, doc := path[0], path[1]
-			fmt.Fprintf(w, "<a href='%s'>%q</a> - %s<br/>", p, p, doc)
-		}
+		httpserver.WriteAPIHelp(w, [][2]string{
+			{"/api/v1/groups", "list all loaded groups and rules"},
+			{"/api/v1/alerts", "list all active alerts"},
+			{"/api/v1/groupID/alertID/status", "get alert status by ID"},
+			{"/metrics", "list of application metrics"},
+			{"/-/reload", "reload configuration"},
+		})
 		return true
 	case "/api/v1/groups":
 		data, err := rh.listGroups()

docs/CHANGELOG.md

@@ -10,6 +10,7 @@ sort: 15
 * FEATURE: add OpenTSDB migration option to vmctl. See more details [here](https://docs.victoriametrics.com/vmctl#migrating-data-from-opentsdb).
 Thanks to @johnseekins!
 * FEATURE: improved new time series registration speed on systems with many CPU cores. See [this issue](https://github.com/VictoriaMetrics/VictoriaMetrics/issues/1244). Thanks to @waldoweng for the idea and [draft implementation](https://github.com/VictoriaMetrics/VictoriaMetrics/pull/1243).
+* FEATURE: vmagent: list user-visible endpoints at `http://vmagent:8429/`. See [this issue](https://github.com/VictoriaMetrics/VictoriaMetrics/issues/1251).
 
 * BUGFIX: vmagent: properly update `role: endpoints` and `role: endpointslices` scrape targets if the underlying service changes in `kubernetes_sd_config`. See [this issue](https://github.com/VictoriaMetrics/VictoriaMetrics/issues/1240).
 * BUGFIX: vmagent: apply `scrape_timeout` on receiving the first response byte from `stream_parse: true` scrape targets. Previously it was applied to receiving and *processing* the full response stream. This could result in false timeout errors when scrape target exposes millions of metrics as described [here](https://github.com/VictoriaMetrics/VictoriaMetrics/issues/1017#issuecomment-767235047).

lib/httpserver/httpserver.go

@@ -11,6 +11,7 @@ import (
 	"net"
 	"net/http"
 	"net/http/pprof"
+	"path"
 	"runtime"
 	"strconv"
 	"strings"
@@ -559,3 +560,12 @@ func IsTLS() bool {
 func GetPathPrefix() string {
 	return *pathPrefix
 }
+
+// WriteAPIHelp writes pathList to w in HTML format.
+func WriteAPIHelp(w io.Writer, pathList [][2]string) {
+	for _, p := range pathList {
+		p, doc := p[0], p[1]
+		p = path.Join(*pathPrefix, p)
+		fmt.Fprintf(w, "<a href=%q>%s</a> - %s<br/>", p, p, doc)
+	}
+}