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,

cmd/frontend/templates/base.html

@@ -34,6 +34,8 @@ a:hover { text-decoration: underline; }
 .error { color: #c00; border: 1px solid #fbb; background: #fff5f5; padding: 0.7em 1em; margin: 1em 0; border-radius: 3px; }
 .nodata { color: #999; margin: 2em 0; font-style: italic; }
 footer { margin-top: 2em; padding-top: 0.6em; border-top: 1px solid #e0e0e0; font-size: 0.8em; color: #999; }
+.tabs-targets { margin-top: -0.4em; }
+.tabs-label { font-size: 0.85em; color: #888; margin-right: 0.2em; align-self: center; }
 .filter-form { display: flex; gap: 0.4em; align-items: center; margin-bottom: 0.7em; }
 .filter-input { flex: 1; font-family: monospace; font-size: 13px; padding: 0.25em 0.5em; border: 1px solid #aaa; }
 .filter-form button { padding: 0.25em 0.8em; border: 1px solid #aaa; background: #f4f4f4; cursor: pointer; font-family: monospace; }

cmd/frontend/templates/index.html

@@ -13,6 +13,13 @@
 {{- end}}
 </div>
 
+{{if .Targets}}<div class="tabs tabs-targets">
+  <span class="tabs-label">source:</span>
+{{- range .Targets}}
+  <a href="{{.URL}}"{{if .Active}} class="active"{{end}}>{{.Label}}</a>
+{{- end}}
+</div>{{end}}
+
 <form class="filter-form" method="get" action="/">
   <input type="hidden" name="target" value="{{.Params.Target}}">
   <input type="hidden" name="w" value="{{.Params.WindowS}}">