From 897d480f4dd723ad0c197e9c9a782da8a4503c7f Mon Sep 17 00:00:00 2001 From: Juan Font Alonso Date: Fri, 4 Mar 2022 00:01:31 +0100 Subject: [PATCH] Add an embedded DERP server to Headscale This series of commit will be adding an embedded DERP server (and STUN) to Headscale, thus making it completely self-contained and not dependant in other infrastructure. --- app.go | 58 ++++++++++-- cmd/headscale/cli/utils.go | 6 ++ derp_embedded.go | 178 +++++++++++++++++++++++++++++++++++++ 3 files changed, 235 insertions(+), 7 deletions(-) create mode 100644 derp_embedded.go diff --git a/app.go b/app.go index 58185093..ee38ed93 100644 --- a/app.go +++ b/app.go @@ -119,6 +119,7 @@ type OIDCConfig struct { } type DERPConfig struct { + EmbeddedDERP bool URLs []url.URL Paths []string AutoUpdate bool @@ -141,7 +142,8 @@ type Headscale struct { dbDebug bool privateKey *key.MachinePrivate - DERPMap *tailcfg.DERPMap + DERPMap *tailcfg.DERPMap + EmbeddedDerpServer *EmbeddedDerpServer aclPolicy *ACLPolicy aclRules []tailcfg.FilterRule @@ -238,6 +240,38 @@ func NewHeadscale(cfg Config) (*Headscale, error) { } } + if cfg.DERP.EmbeddedDERP { + embeddedDerpServer, err := app.NewEmbeddedDerpServer() + if err != nil { + return nil, err + } + app.EmbeddedDerpServer = embeddedDerpServer + + // If we are using the embedded DERP, there is no reason to use Tailscale's DERP infrastructure + serverURL, err := url.Parse(app.cfg.ServerURL) + if err != nil { + return nil, err + } + app.DERPMap = &tailcfg.DERPMap{ + Regions: map[int]*tailcfg.DERPRegion{ + 1: { + RegionID: 1, + RegionCode: "headscale", + RegionName: "Headscale Embedded DERP", + Avoid: false, + Nodes: []*tailcfg.DERPNode{ + { + Name: "1a", + RegionID: 1, + HostName: serverURL.Host, + }, + }, + }, + }, + OmitDefaultRegions: false, + } + } + return &app, nil } @@ -454,6 +488,12 @@ func (h *Headscale) createRouter(grpcMux *runtime.ServeMux) *gin.Engine { router.GET("/swagger", SwaggerUI) router.GET("/swagger/v1/openapiv2.json", SwaggerAPIv1) + if h.cfg.DERP.EmbeddedDERP { + router.Any("/derp", h.EmbeddedDerpHandler) + router.Any("/derp/probe", h.EmbeddedDerpProbeHandler) + router.Any("/bootstrap-dns", h.EmbeddedDerpBootstrapDNSHandler) + } + api := router.Group("/api") api.Use(h.httpAuthenticationMiddleware) { @@ -469,13 +509,17 @@ func (h *Headscale) createRouter(grpcMux *runtime.ServeMux) *gin.Engine { func (h *Headscale) Serve() error { var err error - // Fetch an initial DERP Map before we start serving - h.DERPMap = GetDERPMap(h.cfg.DERP) + if h.cfg.DERP.EmbeddedDERP { + go h.ServeSTUN() + } else { + // Fetch an initial DERP Map before we start serving + h.DERPMap = GetDERPMap(h.cfg.DERP) - if h.cfg.DERP.AutoUpdate { - derpMapCancelChannel := make(chan struct{}) - defer func() { derpMapCancelChannel <- struct{}{} }() - go h.scheduledDERPMapUpdateWorker(derpMapCancelChannel) + if h.cfg.DERP.AutoUpdate { + derpMapCancelChannel := make(chan struct{}) + defer func() { derpMapCancelChannel <- struct{}{} }() + go h.scheduledDERPMapUpdateWorker(derpMapCancelChannel) + } } go h.expireEphemeralNodes(updateInterval) diff --git a/cmd/headscale/cli/utils.go b/cmd/headscale/cli/utils.go index 97c2440e..cff31f32 100644 --- a/cmd/headscale/cli/utils.go +++ b/cmd/headscale/cli/utils.go @@ -117,6 +117,12 @@ func LoadConfig(path string) error { } func GetDERPConfig() headscale.DERPConfig { + if viper.GetBool("derp.embedded_derp") { + return headscale.DERPConfig{ + EmbeddedDERP: true, + } + } + urlStrs := viper.GetStringSlice("derp.urls") urls := make([]url.URL, len(urlStrs)) diff --git a/derp_embedded.go b/derp_embedded.go new file mode 100644 index 00000000..0631fff8 --- /dev/null +++ b/derp_embedded.go @@ -0,0 +1,178 @@ +package headscale + +import ( + "context" + "encoding/json" + "fmt" + "net" + "net/http" + "strings" + "sync/atomic" + "time" + + "github.com/gin-gonic/gin" + "github.com/rs/zerolog/log" + "tailscale.com/derp" + "tailscale.com/net/stun" + "tailscale.com/types/key" +) + +// fastStartHeader is the header (with value "1") that signals to the HTTP +// server that the DERP HTTP client does not want the HTTP 101 response +// headers and it will begin writing & reading the DERP protocol immediately +// following its HTTP request. +const fastStartHeader = "Derp-Fast-Start" + +var ( + dnsCache atomic.Value // of []byte + bootstrapDNS = "derp.tailscale.com" +) + +type EmbeddedDerpServer struct { + tailscaleDerp *derp.Server +} + +func (h *Headscale) NewEmbeddedDerpServer() (*EmbeddedDerpServer, error) { + s := derp.NewServer(key.NodePrivate(*h.privateKey), log.Info().Msgf) + return &EmbeddedDerpServer{s}, nil + +} + +func (h *Headscale) EmbeddedDerpHandler(ctx *gin.Context) { + up := strings.ToLower(ctx.Request.Header.Get("Upgrade")) + if up != "websocket" && up != "derp" { + if up != "" { + log.Warn().Caller().Msgf("Weird websockets connection upgrade: %q", up) + } + ctx.String(http.StatusUpgradeRequired, "DERP requires connection upgrade") + return + } + + fastStart := ctx.Request.Header.Get(fastStartHeader) == "1" + + hijacker, ok := ctx.Writer.(http.Hijacker) + if !ok { + log.Error().Caller().Msg("DERP requires Hijacker interface from Gin") + ctx.String(http.StatusInternalServerError, "HTTP does not support general TCP support") + return + } + + netConn, conn, err := hijacker.Hijack() + if err != nil { + log.Error().Caller().Err(err).Msgf("Hijack failed") + ctx.String(http.StatusInternalServerError, "HTTP does not support general TCP support") + return + } + + if !fastStart { + pubKey := h.privateKey.Public() + fmt.Fprintf(conn, "HTTP/1.1 101 Switching Protocols\r\n"+ + "Upgrade: DERP\r\n"+ + "Connection: Upgrade\r\n"+ + "Derp-Version: %v\r\n"+ + "Derp-Public-Key: %s\r\n\r\n", + derp.ProtocolVersion, + pubKey.UntypedHexString()) + } + + h.EmbeddedDerpServer.tailscaleDerp.Accept(netConn, conn, netConn.RemoteAddr().String()) +} + +// EmbeddedDerpProbeHandler is the endpoint that js/wasm clients hit to measure +// DERP latency, since they can't do UDP STUN queries. +func (h *Headscale) EmbeddedDerpProbeHandler(ctx *gin.Context) { + switch ctx.Request.Method { + case "HEAD", "GET": + ctx.Writer.Header().Set("Access-Control-Allow-Origin", "*") + default: + ctx.String(http.StatusMethodNotAllowed, "bogus probe method") + } +} + +func (h *Headscale) EmbeddedDerpBootstrapDNSHandler(ctx *gin.Context) { + ctx.Header("Content-Type", "application/json") + j, _ := dnsCache.Load().([]byte) + // Bootstrap DNS requests occur cross-regions, + // and are randomized per request, + // so keeping a connection open is pointlessly expensive. + ctx.Header("Connection", "close") + ctx.Writer.Write(j) +} + +// ServeSTUN starts a STUN server on udp/3478 +func (h *Headscale) ServeSTUN() { + pc, err := net.ListenPacket("udp", "0.0.0.0:3478") + if err != nil { + log.Fatal().Msgf("failed to open STUN listener: %v", err) + } + log.Printf("running STUN server on %v", pc.LocalAddr()) + serverSTUNListener(context.Background(), pc.(*net.UDPConn)) +} + +func serverSTUNListener(ctx context.Context, pc *net.UDPConn) { + var buf [64 << 10]byte + var ( + n int + ua *net.UDPAddr + err error + ) + for { + n, ua, err = pc.ReadFromUDP(buf[:]) + if err != nil { + if ctx.Err() != nil { + return + } + log.Printf("STUN ReadFrom: %v", err) + time.Sleep(time.Second) + continue + } + pkt := buf[:n] + if !stun.Is(pkt) { + continue + } + txid, err := stun.ParseBindingRequest(pkt) + if err != nil { + continue + } + + res := stun.Response(txid, ua.IP, uint16(ua.Port)) + pc.WriteTo(res, ua) + } +} + +// Shamelessly taken from +// https://github.com/tailscale/tailscale/blob/main/cmd/derper/bootstrap_dns.go +func refreshBootstrapDNSLoop() { + if bootstrapDNS == "" { + return + } + for { + refreshBootstrapDNS() + time.Sleep(10 * time.Minute) + } +} + +func refreshBootstrapDNS() { + if bootstrapDNS == "" { + return + } + dnsEntries := make(map[string][]net.IP) + ctx, cancel := context.WithTimeout(context.Background(), time.Minute) + defer cancel() + names := strings.Split(bootstrapDNS, ",") + var r net.Resolver + for _, name := range names { + addrs, err := r.LookupIP(ctx, "ip", name) + if err != nil { + log.Printf("bootstrap DNS lookup %q: %v", name, err) + continue + } + dnsEntries[name] = addrs + } + j, err := json.MarshalIndent(dnsEntries, "", "\t") + if err != nil { + // leave the old values in place + return + } + dnsCache.Store(j) +}