[Elastic Agent] Use http2 to connect to Fleet Server. (#26474)

* Use http2 to connect to Fleet Server.

* Add changelog.

* Fix import formatting.

* Fix issue with tls and http2.

(cherry picked from commit 638b62d)

libbeat/common/transport/tls.go

@@ -73,6 +73,63 @@ func TestTLSDialer(
 	}), nil
 }
 
+type DialerH2 interface {
+	Dial(network, address string, cfg *tls.Config) (net.Conn, error)
+}
+
+type DialerFuncH2 func(network, address string, cfg *tls.Config) (net.Conn, error)
+
+func (d DialerFuncH2) Dial(network, address string, cfg *tls.Config) (net.Conn, error) {
+	return d(network, address, cfg)
+}
+
+func TLSDialerH2(forward Dialer, config *tlscommon.TLSConfig, timeout time.Duration) (DialerH2, error) {
+	return TestTLSDialerH2(testing.NullDriver, forward, config, timeout)
+}
+
+func TestTLSDialerH2(
+	d testing.Driver,
+	forward Dialer,
+	config *tlscommon.TLSConfig,
+	timeout time.Duration,
+) (DialerH2, error) {
+	var lastTLSConfig *tls.Config
+	var lastNetwork string
+	var lastAddress string
+	var m sync.Mutex
+
+	return DialerFuncH2(func(network, address string, cfg *tls.Config) (net.Conn, error) {
+		switch network {
+		case "tcp", "tcp4", "tcp6":
+		default:
+			return nil, fmt.Errorf("unsupported network type %v", network)
+		}
+
+		host, _, err := net.SplitHostPort(address)
+		if err != nil {
+			return nil, err
+		}
+
+		var tlsConfig *tls.Config
+		m.Lock()
+		if network == lastNetwork && address == lastAddress {
+			tlsConfig = lastTLSConfig
+		}
+		if tlsConfig == nil {
+			tlsConfig = config.BuildModuleClientConfig(host)
+			lastNetwork = network
+			lastAddress = address
+			lastTLSConfig = tlsConfig
+		}
+		m.Unlock()
+
+		// NextProtos must be set from the passed h2 connection or it will fail
+		tlsConfig.NextProtos = cfg.NextProtos
+
+		return tlsDialWith(d, forward, network, address, timeout, tlsConfig, config)
+	}), nil
+}
+
 func tlsDialWith(
 	d testing.Driver,
 	dialer Dialer,

x-pack/elastic-agent/CHANGELOG.next.asciidoc

@@ -116,3 +116,4 @@
 - Use `filestream` input for internal log collection. {pull}25660[25660]
 - Enable agent to send custom headers to kibana/ES {pull}26275[26275]
 - Set `agent.id` to the Fleet Agent ID in events published from inputs backed by Beats. {issue}21121[21121] {pull}26394[26394]
+- Communicate with Fleet Server over HTTP2. {pull}26474[26474]

x-pack/elastic-agent/pkg/remote/client.go

@@ -15,6 +15,7 @@ import (
 	"time"
 
 	"github.com/pkg/errors"
+	"golang.org/x/net/http2"
 
 	"github.com/elastic/beats/v7/libbeat/common"
 	"github.com/elastic/beats/v7/libbeat/common/transport"
@@ -113,8 +114,16 @@ func NewWithConfig(log *logger.Logger, cfg Config, wrapper wrapperFunc) (*Client
 	hosts := cfg.GetHosts()
 	clients := make([]*requestClient, len(hosts))
 	for i, host := range cfg.GetHosts() {
-		var transport http.RoundTripper
-		transport, err := makeTransport(cfg.Timeout, cfg.TLS)
+		connStr, err := common.MakeURL(string(cfg.Protocol), p, host, 0)
+		if err != nil {
+			return nil, errors.Wrap(err, "invalid fleet-server endpoint")
+		}
+		addr, err := url.Parse(connStr)
+		if err != nil {
+			return nil, errors.Wrap(err, "invalid fleet-server endpoint")
+		}
+
+		transport, err := makeTransport(addr.Scheme, cfg.Timeout, cfg.TLS)
 		if err != nil {
 			return nil, err
 		}
@@ -136,12 +145,8 @@ func NewWithConfig(log *logger.Logger, cfg Config, wrapper wrapperFunc) (*Client
 			Timeout:   cfg.Timeout,
 		}
 
-		url, err := common.MakeURL(string(cfg.Protocol), p, host, 0)
-		if err != nil {
-			return nil, errors.Wrap(err, "invalid fleet-server endpoint")
-		}
 		clients[i] = &requestClient{
-			request: prefixRequestFactory(url),
+			request: prefixRequestFactory(connStr),
 			client:  httpClient,
 		}
 	}
@@ -272,17 +277,18 @@ func prefixRequestFactory(URL string) requestFunc {
 }
 
 // makeTransport create a transport object based on the TLS configuration.
-func makeTransport(timeout time.Duration, tls *tlscommon.Config) (*http.Transport, error) {
+func makeTransport(scheme string, timeout time.Duration, tls *tlscommon.Config) (http.RoundTripper, error) {
+	dialer := transport.NetDialer(timeout)
+	if scheme == "http" {
+		return &http.Transport{Dial: dialer.Dial}, nil
+	}
 	tlsConfig, err := tlscommon.LoadTLSConfig(tls)
 	if err != nil {
 		return nil, errors.Wrap(err, "invalid TLS configuration")
 	}
-	dialer := transport.NetDialer(timeout)
-	tlsDialer, err := transport.TLSDialer(dialer, tlsConfig, timeout)
+	tlsDialer, err := transport.TLSDialerH2(dialer, tlsConfig, timeout)
 	if err != nil {
 		return nil, errors.Wrap(err, "fail to create TLS dialer")
 	}
-
-	// TODO: Dial is deprecated we need to move to DialContext.
-	return &http.Transport{Dial: dialer.Dial, DialTLS: tlsDialer.Dial}, nil
+	return &http2.Transport{DialTLS: tlsDialer.Dial}, nil
 }