some tweaks to cart

pkg/proxy/remotehost.go

@@ -9,6 +9,7 @@ import (
 	"io"
 	"log"
 	"net/http"
+	"sync"
 	"time"
 
 	"git.k6n.net/mats/go-cart-actor/pkg/actor"
@@ -27,7 +28,6 @@ type RemoteHost[V any] struct {
 	host          string
 	httpBase      string
 	conn          *grpc.ClientConn
-	transport     *http.Transport
 	client        *http.Client
 	controlClient messages.ControlPlaneClient
 	missedPings   int
@@ -38,8 +38,27 @@ const name = "proxy"
 var (
 	tracer = otel.Tracer(name)
 	meter  = otel.Meter(name)
+
+	// One process-wide HTTP transport pools idle connections to every peer.
+	// Per-host RemoteHost instances previously each owned a transport with
+	// MaxIdleConnsPerHost=100, multiplying file handles by replica count.
+	sharedTransport     *http.Transport
+	sharedTransportOnce sync.Once
 )
 
+func sharedHTTPTransport() *http.Transport {
+	sharedTransportOnce.Do(func() {
+		sharedTransport = &http.Transport{
+			MaxIdleConns:        64,
+			MaxIdleConnsPerHost: 8,
+			MaxConnsPerHost:     32,
+			DisableKeepAlives:   false,
+			IdleConnTimeout:     90 * time.Second,
+		}
+	})
+	return sharedTransport
+}
+
 // MockResponseWriter implements http.ResponseWriter to capture responses for proxy calls.
 type MockResponseWriter struct {
 	StatusCode int
@@ -88,23 +107,13 @@ func NewRemoteHost[V any](host string, httpPort ...string) (*RemoteHost[V], erro
 
 	controlClient := messages.NewControlPlaneClient(conn)
 
-	transport := &http.Transport{
-		MaxIdleConns:        100,
-		MaxIdleConnsPerHost: 100,
-		// Bound concurrently-open connections to this peer so a load spike
-		// can't exhaust file handles. Excess requests wait for a free conn
-		// rather than opening unbounded sockets.
-		MaxConnsPerHost:   256,
-		DisableKeepAlives: false,
-		IdleConnTimeout:   120 * time.Second,
-	}
+	transport := sharedHTTPTransport()
 	client := &http.Client{Transport: transport, Timeout: 10 * time.Second}
 
 	return &RemoteHost[V]{
 		host:          host,
 		httpBase:      fmt.Sprintf("http://%s:%s", host, port),
 		conn:          conn,
-		transport:     transport,
 		client:        client,
 		controlClient: controlClient,
 		missedPings:   0,
@@ -136,7 +145,9 @@ func (h *RemoteHost[V]) Name() string {
 
 func (h *RemoteHost[V]) Close() error {
 	if h.conn != nil {
-		h.conn.Close()
+		err := h.conn.Close()
+		h.conn = nil
+		return err
 	}
 	return nil
 }