http-connect: reduce memory allocations

Introduce a `sync.Pool` to reuse read buffers in the `ServeHTTP` handler
for the http-connect mode.

Previously, a new 32KB buffer was allocated for every hijacked
connection, causing high GC pressure in high-throughput scenarios.  By
pooling and reusing these buffers, we significantly reduce the number of
memory allocations, which improves CPU usage and lowers request latency
by decreasing the impact of garbage collection.

Signed-off-by: Imran Pochi <[email protected]>

Author: ipochi

pkg/server/tunnel.go

@@ -29,6 +29,22 @@ import (
 	"sigs.k8s.io/apiserver-network-proxy/pkg/server/metrics"
 )
 
+const (
+	// bufferSize is the size of the buffer used for reading from the hijacked connection.
+	// It matches the gRPC window size for optimal performance.
+	bufferSize = 1 << 15 // 32KB
+)
+
+// bufferPool is a pool of byte slices used for reading data from hijacked connections.
+// This reduces memory allocations and GC pressure by reusing buffers across connections.
+var bufferPool = sync.Pool{
+	New: func() interface{} {
+		// Allocate a new buffer when the pool is empty
+		buf := make([]byte, bufferSize)
+		return &buf
+	},
+}
+
 // Tunnel implements Proxy based on HTTP Connect, which tunnels the traffic to
 // the agent registered in ProxyServer.
 type Tunnel struct {
@@ -176,7 +192,14 @@ func (t *Tunnel) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 	agentID := connection.agentID
 	klog.V(3).InfoS("Starting proxy to host", "host", r.Host, "agentID", agentID, "connectionID", connID)
 
-	pkt := make([]byte, 1<<15) // Match GRPC Window size
+	// Get a buffer from the pool
+	bufPtr := bufferPool.Get().(*[]byte)
+	pkt := *bufPtr
+	defer func() {
+		// Return the buffer to the pool when done
+		bufferPool.Put(bufPtr)
+	}()
+
 	var acc int
 
 	for {