pkg/receive: forward metrics

This commit enables metrics forwarding from one receive node to another.
The receive nodes construct hashrings from the given sd-files and
use these hashrings to select a node to which toforward a given time
series. Time series are batched together to ensure that for any incoming
write-request to a node, at most one outgoing write-request will be made
every other node in the hashring.

cmd/thanos/receive.go

@@ -4,6 +4,8 @@ import (
 	"context"
 	"fmt"
 	"net"
+	"os"
+	"strings"
 	"time"
 
 	"github.com/go-kit/kit/log"
@@ -45,12 +47,42 @@ func registerReceive(m map[string]setupFunc, app *kingpin.Application, name stri
 
 	retention := modelDuration(cmd.Flag("tsdb.retention", "How long to retain raw samples on local storage. 0d - disables this retention").Default("15d"))
 
+	hashringsFile := cmd.Flag("receive.hashrings-file", "Path to file that contains the hashring configuration.").
+		PlaceHolder("<path>").String()
+
+	refreshInterval := modelDuration(cmd.Flag("receive.hashrings-file-refresh-interval", "Refresh interval to re-read the hashring configuration file. (used as a fallback)").
+		Default("5m"))
+
+	local := cmd.Flag("receive.local-endpoint", "Endpoint of local receive node. Used to identify the local node in the hashring configuration.").String()
+
+	tenantHeader := cmd.Flag("receive.tenant-header", "HTTP header to determine tenant for write requests.").Default("THANOS-TENANT").String()
+
 	m[name] = func(g *run.Group, logger log.Logger, reg *prometheus.Registry, tracer opentracing.Tracer, _ bool) error {
 		lset, err := parseFlagLabels(*labelStrs)
 		if err != nil {
 			return errors.Wrap(err, "parse labels")
 		}
 
+		var cw *receive.ConfigWatcher
+		if *hashringsFile != "" {
+			cw, err = receive.NewConfigWatcher(log.With(logger, "component", "config-watcher"), reg, *hashringsFile, *refreshInterval)
+			if err != nil {
+				return err
+			}
+		}
+
+		// Local is empty, so try to generate a local endpoint
+		// based on the hostname and the listening port.
+		if *local == "" {
+			hostname, err := os.Hostname()
+			if hostname == "" || err != nil {
+				return errors.New("--receive.local-endpoint is empty and host could not be determined.")
+			}
+			parts := strings.Split(*remoteWriteAddress, ":")
+			port := parts[len(parts)-1]
+			*local = fmt.Sprintf("http://%s:%s/api/v1/receive", hostname, port)
+		}
+
 		return runReceive(
 			g,
 			logger,
@@ -66,6 +98,9 @@ func registerReceive(m map[string]setupFunc, app *kingpin.Application, name stri
 			objStoreConfig,
 			lset,
 			*retention,
+			cw,
+			*local,
+			*tenantHeader,
 		)
 	}
 }
@@ -85,6 +120,9 @@ func runReceive(
 	objStoreConfig *pathOrContent,
 	lset labels.Labels,
 	retention model.Duration,
+	cw *receive.ConfigWatcher,
+	endpoint string,
+	tenantHeader string,
 ) error {
 	logger = log.With(logger, "component", "receive")
 	level.Warn(logger).Log("msg", "setting up receive; the Thanos receive component is EXPERIMENTAL, it may break significantly without notice")
@@ -103,6 +141,8 @@ func runReceive(
 		ListenAddress: remoteWriteAddress,
 		Registry:      reg,
 		ReadyStorage:  localStorage,
+		Endpoint:      endpoint,
+		TenantHeader:  tenantHeader,
 	})
 
 	// Start all components while we wait for TSDB to open but only load
@@ -129,7 +169,7 @@ func runReceive(
 
 				startTimeMargin := int64(2 * time.Duration(tsdbCfg.MinBlockDuration).Seconds() * 1000)
 				localStorage.Set(db, startTimeMargin)
-				webHandler.Ready()
+				webHandler.StorageReady()
 				level.Info(logger).Log("msg", "server is ready to receive web requests.")
 				close(dbOpen)
 				<-cancel
@@ -144,6 +184,56 @@ func runReceive(
 		)
 	}
 
+	level.Debug(logger).Log("msg", "setting up hashring")
+	{
+		updates := make(chan receive.Hashring)
+		if cw != nil {
+			ctx, cancel := context.WithCancel(context.Background())
+			g.Add(func() error {
+				receive.HashringFromConfig(ctx, updates, cw)
+				return nil
+			}, func(error) {
+				cancel()
+				close(updates)
+			})
+		} else {
+			cancel := make(chan struct{})
+			g.Add(func() error {
+				updates <- receive.SingleNodeHashring(endpoint)
+				<-cancel
+				return nil
+			}, func(error) {
+				close(cancel)
+				close(updates)
+			})
+		}
+
+		cancel := make(chan struct{})
+		g.Add(
+			func() error {
+				select {
+				case h := <-updates:
+					webHandler.Hashring(h)
+				case <-cancel:
+					return nil
+				}
+				select {
+				// If any new hashring is received, then mark the handler as unready, but keep it alive.
+				case <-updates:
+					webHandler.Hashring(nil)
+					level.Info(logger).Log("msg", "hashring has changed; server is not ready to receive web requests.")
+				case <-cancel:
+					return nil
+				}
+				<-cancel
+				return nil
+			},
+			func(err error) {
+				close(cancel)
+			},
+		)
+	}
+
 	level.Debug(logger).Log("msg", "setting up metric http listen-group")
 	if err := metricHTTPListenGroup(g, logger, reg, httpMetricsBindAddr); err != nil {
 		return err

go.mod

@@ -47,6 +47,7 @@ require (
 	google.golang.org/api v0.3.2
 	google.golang.org/grpc v1.19.1
 	gopkg.in/alecthomas/kingpin.v2 v2.2.6
+	gopkg.in/fsnotify.v1 v1.4.7
 	gopkg.in/fsnotify/fsnotify.v1 v1.4.7 // indirect
 	gopkg.in/yaml.v2 v2.2.2
 )