added option to map a cname host to a local origin

cmd/cloudflared/tunnel/cmd.go

@@ -768,6 +768,12 @@ func tunnelFlags(shouldHide bool) []cli.Flag {
 			EnvVars: []string{"TUNNEL_HOSTNAME"},
 			Hidden:  shouldHide,
 		}),
+		altsrc.NewStringSliceFlag(&cli.StringSliceFlag{
+			Name:    "host-to-origin",
+			Usage:   "Decalre a direct host to origin mapping i.e. host1.example.com=http://localhost:8080. This takes precedence over the single url mapping.",
+			EnvVars: []string{"HOST_TO_ORIGIN"},
+			Hidden:  shouldHide,
+		}),
 		altsrc.NewStringFlag(&cli.StringFlag{
 			Name:    "http-host-header",
 			Usage:   "Sets the HTTP Host header for the local webserver.",

cmd/cloudflared/tunnel/configuration.go

@@ -71,7 +71,7 @@ func logClientOptions(c *cli.Context) {
 		flags[flag] = c.Generic(flag)
 	}
 
-	sliceFlags := []string{"header", "tag", "proxy-dns-upstream", "upstream", "edge"}
+	sliceFlags := []string{"header", "tag", "proxy-dns-upstream", "upstream", "edge", "host-to-origin"}
 	for _, sliceFlag := range sliceFlags {
 		if len(c.StringSlice(sliceFlag)) > 0 {
 			flags[sliceFlag] = strings.Join(c.StringSlice(sliceFlag), ", ")
@@ -179,6 +179,15 @@ func prepareTunnelConfig(
 		return nil, errors.Wrap(err, "Error validating origin URL")
 	}
 
+	hostToOriginUrls := make(map[string]string)
+	hostToOrigins := c.StringSlice("host-to-origin")
+	for _, hostToOrigin := range hostToOrigins {
+		hostToOriginArr := strings.Split(hostToOrigin, "=")
+		if len(hostToOriginArr) == 2 {
+			hostToOriginUrls[hostToOriginArr[0]] = hostToOriginArr[1]
+		}
+	}
+
 	var originCert []byte
 	if !isFreeTunnel {
 		originCert, err = getOriginCert(c)
@@ -268,6 +277,7 @@ func prepareTunnelConfig(
 		NoChunkedEncoding:    c.Bool("no-chunked-encoding"),
 		OriginCert:           originCert,
 		OriginUrl:            originURL,
+		HostToOriginUrls:     hostToOriginUrls,
 		ReportedVersion:      version,
 		Retries:              c.Uint("retries"),
 		RunFromTerminal:      isRunningFromTerminal(),

origin/tunnel.go

@@ -85,6 +85,8 @@ type TunnelConfig struct {
 	// OriginUrl may not be used if a user specifies a unix socket.
 	OriginUrl string
 
+	// Optional mapping to enable routing to multiple OriginUrls based on Host header.
+	HostToOriginUrls map[string]string
 	// feature-flag to use new edge reconnect tokens
 	UseReconnectToken bool
 	// feature-flag for using ConnectionDigest
@@ -540,6 +542,7 @@ func LogServerInfo(
 
 type TunnelHandler struct {
 	originUrl      string
+	hostToOriginUrls map[string]string
 	httpHostHeader string
 	muxer          *h2mux.Muxer
 	httpClient     http.RoundTripper
@@ -565,8 +568,16 @@ func NewTunnelHandler(ctx context.Context,
 	if err != nil {
 		return nil, "", fmt.Errorf("unable to parse origin URL %#v", originURL)
 	}
+	for k, _ := range config.HostToOriginUrls {
+		hostOriginURL, err := validation.ValidateUrl(config.HostToOriginUrls[k])
+		if err != nil {
+			return nil, "", fmt.Errorf("unable to parse origin URL %#v", hostOriginURL)
+		}
+		config.HostToOriginUrls[k] = hostOriginURL
+	}
 	h := &TunnelHandler{
 		originUrl:         originURL,
+		hostToOriginUrls:  config.HostToOriginUrls,
 		httpHostHeader:    config.HTTPHostHeader,
 		httpClient:        config.HTTPTransport,
 		tlsConfig:         config.ClientTlsConfig,
@@ -629,8 +640,27 @@ func (h *TunnelHandler) ServeStream(stream *h2mux.MuxedStream) error {
 	return nil
 }
 
+func getOriginUrlForHost(h2 []h2mux.Header, hostToOriginUrls map[string]string) (string, string) {
+	host := ""
+	for _, header := range h2 {
+		switch strings.ToLower(header.Name) {
+		case ":authority":
+			host := header.Value
+			if val, ok := hostToOriginUrls[header.Value]; ok {
+			    return host, val
+			}
+		}
+	}
+	return host, ""
+}
+
 func (h *TunnelHandler) createRequest(stream *h2mux.MuxedStream) (*http.Request, error) {
-	req, err := http.NewRequest("GET", h.originUrl, h2mux.MuxedStreamReader{MuxedStream: stream})
+	host, origin := getOriginUrlForHost(stream.Headers, h.hostToOriginUrls)
+
+	if host == "" {
+		origin = h.originUrl
+	}
+	req, err := http.NewRequest("GET", origin, h2mux.MuxedStreamReader{MuxedStream: stream})
 	if err != nil {
 		return nil, errors.Wrap(err, "Unexpected error from http.NewRequest")
 	}