fix: stop redirecting DERP and replicasync http requests (#10752)

Fixes an issue where setting CODER_REDIRECT_TO_ACCESS_URL breaks use of multiple Coder server replicas for DERP traffic.

enterprise/replicasync/replicasync.go

@@ -7,6 +7,7 @@ import (
 	"errors"
 	"fmt"
 	"net/http"
+	"net/url"
 	"os"
 	"strings"
 	"sync"
@@ -274,7 +275,19 @@ func (m *Manager) syncReplicas(ctx context.Context) error {
 		wg.Add(1)
 		go func(peer database.Replica) {
 			defer wg.Done()
-			req, err := http.NewRequestWithContext(ctx, http.MethodGet, peer.RelayAddress, nil)
+			ra, err := url.Parse(peer.RelayAddress)
+			if err != nil {
+				m.logger.Warn(ctx, "could not parse relay address",
+					slog.F("relay_address", peer.RelayAddress), slog.Error(err))
+				return
+			}
+			target, err := ra.Parse("/derp/latency-check")
+			if err != nil {
+				m.logger.Warn(ctx, "could not resolve /derp/latency-check endpoint",
+					slog.F("relay_address", peer.RelayAddress), slog.Error(err))
+				return
+			}
+			req, err := http.NewRequestWithContext(ctx, http.MethodGet, target.String(), nil)
 			if err != nil {
 				m.logger.Warn(ctx, "create http request for relay probe",
 					slog.F("relay_address", peer.RelayAddress), slog.Error(err))

enterprise/replicasync/replicasync_test.go

@@ -7,6 +7,7 @@ import (
 	"net/http"
 	"net/http/httptest"
 	"sync"
+	"sync/atomic"
 	"testing"
 	"time"
 
@@ -55,9 +56,9 @@ func TestReplica(t *testing.T) {
 		// Ensures that the replica reports a successful status for
 		// accessing all of its peers.
 		t.Parallel()
-		srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
-			w.WriteHeader(http.StatusOK)
-		}))
+		dh := &derpyHandler{}
+		defer dh.requireOnlyDERPPaths(t)
+		srv := httptest.NewServer(dh)
 		defer srv.Close()
 		db, pubsub := dbtestutil.NewDB(t)
 		peer, err := db.InsertReplica(context.Background(), database.InsertReplicaParams{
@@ -98,9 +99,9 @@ func TestReplica(t *testing.T) {
 			ServerName:   "hello.org",
 			RootCAs:      pool,
 		}
-		srv := httptest.NewUnstartedServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
-			w.WriteHeader(http.StatusOK)
-		}))
+		dh := &derpyHandler{}
+		defer dh.requireOnlyDERPPaths(t)
+		srv := httptest.NewUnstartedServer(dh)
 		srv.TLS = tlsConfig
 		srv.StartTLS()
 		defer srv.Close()
@@ -167,9 +168,9 @@ func TestReplica(t *testing.T) {
 		server, err := replicasync.New(ctx, slogtest.Make(t, nil), db, pubsub, nil)
 		require.NoError(t, err)
 		defer server.Close()
-		srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
-			w.WriteHeader(http.StatusOK)
-		}))
+		dh := &derpyHandler{}
+		defer dh.requireOnlyDERPPaths(t)
+		srv := httptest.NewServer(dh)
 		defer srv.Close()
 		peer, err := db.InsertReplica(ctx, database.InsertReplicaParams{
 			ID:           uuid.New(),
@@ -221,9 +222,9 @@ func TestReplica(t *testing.T) {
 		db := dbmem.New()
 		pubsub := pubsub.NewInMemory()
 		logger := slogtest.Make(t, nil)
-		srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
-			w.WriteHeader(http.StatusOK)
-		}))
+		dh := &derpyHandler{}
+		defer dh.requireOnlyDERPPaths(t)
+		srv := httptest.NewServer(dh)
 		defer srv.Close()
 		var wg sync.WaitGroup
 		count := 20
@@ -255,3 +256,20 @@ func TestReplica(t *testing.T) {
 		wg.Wait()
 	})
 }
+
+type derpyHandler struct {
+	atomic.Uint32
+}
+
+func (d *derpyHandler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
+	if r.URL.Path != "/derp/latency-check" {
+		w.WriteHeader(http.StatusNotFound)
+		d.Add(1)
+		return
+	}
+	w.WriteHeader(http.StatusUpgradeRequired)
+}
+
+func (d *derpyHandler) requireOnlyDERPPaths(t *testing.T) {
+	require.Equal(t, uint32(0), d.Load())
+}