Implement target selection, autodiscovery via aggregator, implement listTargets

cmd/frontend/handler.go

@@ -76,6 +76,7 @@ type PageData struct {
 	Breadcrumbs    []Crumb
 	Windows        []Tab
 	GroupBys       []Tab
+	Targets        []Tab // source/target picker; empty when only one target available
 	RefreshSecs    int
 	Error          string
 	FilterExpr     string // current filter serialised to mini-language for the input box
@@ -340,6 +341,38 @@ func buildGroupByTabs(p QueryParams) []Tab {
 	return tabs
 }
 
+// buildTargetTabs builds the source/target picker tabs from a ListTargets response.
+// Returns nil (hide picker) when only one endpoint is reachable.
+func (h *Handler) buildTargetTabs(p QueryParams, lt *pb.ListTargetsResponse) []Tab {
+	// "all" always points at the configured aggregator default.
+	allTab := Tab{
+		Label:  "all",
+		URL:    p.buildURL(map[string]string{"target": h.defaultTarget}),
+		Active: p.Target == h.defaultTarget,
+	}
+
+	var collectorTabs []Tab
+	if lt != nil {
+		for _, t := range lt.Targets {
+			addr := t.Addr
+			if addr == "" {
+				addr = p.Target // collector reporting itself; addr is the current target
+			}
+			collectorTabs = append(collectorTabs, Tab{
+				Label:  t.Name,
+				URL:    p.buildURL(map[string]string{"target": addr}),
+				Active: p.Target == addr,
+			})
+		}
+	}
+
+	// Only render the picker when there is more than one choice.
+	if len(collectorTabs) == 0 {
+		return nil
+	}
+	return append([]Tab{allTab}, collectorTabs...)
+}
+
 func buildTableRows(entries []*pb.TopNEntry, p QueryParams) ([]TableRow, int64) {
 	if len(entries) == 0 {
 		return nil, 0
@@ -410,6 +443,7 @@ func (h *Handler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 	}
 	topNCh := make(chan topNResult, 1)
 	trendCh := make(chan trendResult, 1)
+	ltCh := make(chan *pb.ListTargetsResponse, 1)
 
 	go func() {
 		resp, err := client.TopN(ctx, &pb.TopNRequest{
@@ -427,9 +461,18 @@ func (h *Handler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 		})
 		trendCh <- trendResult{resp, err}
 	}()
+	go func() {
+		resp, err := client.ListTargets(ctx, &pb.ListTargetsRequest{})
+		if err != nil {
+			ltCh <- nil
+		} else {
+			ltCh <- resp
+		}
+	}()
 
 	tn := <-topNCh
 	tr := <-trendCh
+	lt := <-ltCh
 
 	if tn.err != nil {
 		h.render(w, http.StatusBadGateway, h.errorPage(params,
@@ -459,6 +502,7 @@ func (h *Handler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 		Breadcrumbs:    buildCrumbs(params),
 		Windows:        buildWindowTabs(params),
 		GroupBys:       buildGroupByTabs(params),
+		Targets:        h.buildTargetTabs(params, lt),
 		RefreshSecs:    h.refreshSecs,
 		FilterExpr:     filterExprInput,
 		FilterErr:      filterErr,