Added support for tail to query frontend (grafana#2032)

* Added support for tail to query frontend

* cleanup WsTailProxy

* used httputil.NewSingleHostReverseProxy insted of custom implementation, added tailproxy config

* proxy all unknown requests

* rename proxy to tailProxy

* default handler, if tailproxy url is set up default proxy is tailproxy

* embedded lokifrontend conf which adds tail_proxy_url

* fixed tail_proxy_url flag

pkg/loki/loki.go

@@ -29,6 +29,7 @@ import (
 	"github.com/grafana/loki/pkg/distributor"
 	"github.com/grafana/loki/pkg/ingester"
 	"github.com/grafana/loki/pkg/ingester/client"
+	"github.com/grafana/loki/pkg/lokifrontend"
 	"github.com/grafana/loki/pkg/querier"
 	"github.com/grafana/loki/pkg/querier/queryrange"
 	"github.com/grafana/loki/pkg/storage"
@@ -54,7 +55,7 @@ type Config struct {
 	LimitsConfig     validation.Limits           `yaml:"limits_config,omitempty"`
 	TableManager     chunk.TableManagerConfig    `yaml:"table_manager,omitempty"`
 	Worker           frontend.WorkerConfig       `yaml:"frontend_worker,omitempty"`
-	Frontend         frontend.Config             `yaml:"frontend,omitempty"`
+	Frontend         lokifrontend.Config         `yaml:"frontend,omitempty"`
 	QueryRange       queryrange.Config           `yaml:"query_range,omitempty"`
 	RuntimeConfig    runtimeconfig.ManagerConfig `yaml:"runtime_config,omitempty"`
 	MemberlistKV     memberlist.KVConfig         `yaml:"memberlist"`

pkg/loki/modules.go

@@ -4,6 +4,8 @@ import (
 	"errors"
 	"fmt"
 	"net/http"
+	"net/http/httputil"
+	"net/url"
 	"os"
 	"sort"
 	"time"
@@ -267,7 +269,7 @@ func (t *Loki) initStore() (_ services.Service, err error) {
 
 func (t *Loki) initQueryFrontend() (_ services.Service, err error) {
 	level.Debug(util.Logger).Log("msg", "initializing query frontend", "config", fmt.Sprintf("%+v", t.cfg.Frontend))
-	t.frontend, err = frontend.New(t.cfg.Frontend, util.Logger, prometheus.DefaultRegisterer)
+	t.frontend, err = frontend.New(t.cfg.Frontend.Config, util.Logger, prometheus.DefaultRegisterer)
 	if err != nil {
 		return
 	}
@@ -297,6 +299,21 @@ func (t *Loki) initQueryFrontend() (_ services.Service, err error) {
 		serverutil.NewPrepopulateMiddleware(),
 	).Wrap(t.frontend.Handler())
 
+	var defaultHandler http.Handler
+	if t.cfg.Frontend.TailProxyUrl != "" {
+		httpMiddleware := middleware.Merge(
+			t.httpAuthMiddleware,
+			queryrange.StatsHTTPMiddleware,
+		)
+		tailURL, err := url.Parse(t.cfg.Frontend.TailProxyUrl)
+		if err != nil {
+			return nil, err
+		}
+		tp := httputil.NewSingleHostReverseProxy(tailURL)
+		defaultHandler = httpMiddleware.Wrap(tp)
+	} else {
+		defaultHandler = frontendHandler
+	}
 	t.server.HTTP.Handle("/loki/api/v1/query_range", frontendHandler)
 	t.server.HTTP.Handle("/loki/api/v1/query", frontendHandler)
 	t.server.HTTP.Handle("/loki/api/v1/label", frontendHandler)
@@ -308,7 +325,7 @@ func (t *Loki) initQueryFrontend() (_ services.Service, err error) {
 	t.server.HTTP.Handle("/api/prom/label/{name}/values", frontendHandler)
 	t.server.HTTP.Handle("/api/prom/series", frontendHandler)
 	// fallback route
-	t.server.HTTP.PathPrefix("/").Handler(frontendHandler)
+	t.server.HTTP.PathPrefix("/").Handler(defaultHandler)
 
 	return services.NewIdleService(nil, func(_ error) error {
 		t.frontend.Close()

pkg/lokifrontend/config.go

@@ -0,0 +1,17 @@
+package lokifrontend
+
+import (
+	"flag"
+	"github.com/cortexproject/cortex/pkg/querier/frontend"
+)
+
+type Config struct {
+	frontend.Config `yaml:",inline"`
+	TailProxyUrl    string `yaml:"tail_proxy_url"`
+}
+
+// RegisterFlags adds the flags required to config this to the given FlagSet.
+func (cfg *Config) RegisterFlags(f *flag.FlagSet) {
+	cfg.Config.RegisterFlags(f)
+	f.StringVar(&cfg.TailProxyUrl, "frontend.tail-proxy-url", "", "URL of querier for tail proxy.")
+}