Add receiver downscale endpoint (#88)

Author: yuchen-db

cmd/thanos/receive.go

@@ -7,8 +7,10 @@ import (
 	"context"
 	"fmt"
 	"net"
+	"net/http"
 	"os"
 	"path"
+	"strconv"
 	"strings"
 	"time"
 
@@ -322,6 +324,19 @@ func runReceive(
 			httpserver.WithGracePeriod(time.Duration(*conf.httpGracePeriod)),
 			httpserver.WithTLSConfig(*conf.httpTLSConfig),
 		)
+		srv.Handle("/-/downscale", http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+			tenants := dbs.GetTenants()
+			n := len(tenants)
+			w.Header().Set("Tenant-Count", strconv.Itoa(n))
+			for _, tname := range tenants {
+				w.Header().Add("Tenants", tname)
+			}
+			if n > 0 {
+				w.WriteHeader(http.StatusTooEarly)
+			} else {
+				w.WriteHeader(http.StatusOK)
+			}
+		}))
 		g.Add(func() error {
 			statusProber.Healthy()
 			return srv.ListenAndServe()
@@ -465,7 +480,7 @@ func runReceive(
 		ctx, cancel := context.WithCancel(context.Background())
 		g.Add(func() error {
 			return runutil.Repeat(conf.topMetricsUpdateInterval, ctx.Done(), func() error {
-				level.Info(logger).Log("msg", "getting top metrics")
+				level.Debug(logger).Log("msg", "getting top metrics")
 				for _, ts := range dbs.TenantStats(conf.numTopMetricsPerTenant, labels.MetricName) {
 					for _, ms := range ts.Stats.IndexPostingStats.CardinalityMetricsStats {
 						if ms.Count >= conf.topMetricsMinimumCardinality {

pkg/receive/multitsdb.go

@@ -122,6 +122,16 @@ func NewMultiTSDB(
 	return mt
 }
 
+func (t *MultiTSDB) GetTenants() []string {
+	t.mtx.RLock()
+	tenants := make([]string, 0, len(t.tenants))
+	for tname := range t.tenants {
+		tenants = append(tenants, tname)
+	}
+	defer t.mtx.RUnlock()
+	return tenants
+}
+
 type localClient struct {
 	store *store.TSDBStore