TUN-2714: New edge discovery. Connections try to reconnect to the same edge IP.

edgediscovery/allregions/discovery.go

@@ -0,0 +1,135 @@
+package allregions
+
+import (
+	"context"
+	"crypto/tls"
+	"fmt"
+	"net"
+	"time"
+
+	"github.com/pkg/errors"
+	"github.com/sirupsen/logrus"
+)
+
+const (
+	// Used to discover HA origintunneld servers
+	srvService = "origintunneld"
+	srvProto   = "tcp"
+	srvName    = "argotunnel.com"
+
+	// Used to fallback to DoT when we can't use the default resolver to
+	// discover HA origintunneld servers (GitHub issue #75).
+	dotServerName = "cloudflare-dns.com"
+	dotServerAddr = "1.1.1.1:853"
+	dotTimeout    = time.Duration(15 * time.Second)
+
+	// SRV record resolution TTL
+	resolveEdgeAddrTTL = 1 * time.Hour
+
+	subsystemEdgeAddrResolver = "edgeAddrResolver"
+)
+
+// Redeclare network functions so they can be overridden in tests.
+var (
+	netLookupSRV = net.LookupSRV
+	netLookupIP  = net.LookupIP
+)
+
+// If the call to net.LookupSRV fails, try to fall back to DoT from Cloudflare directly.
+//
+// Note: Instead of DoT, we could also have used DoH. Either of these:
+//     - directly via the JSON API (https://1.1.1.1/dns-query?ct=application/dns-json&name=_origintunneld._tcp.argotunnel.com&type=srv)
+//     - indirectly via `tunneldns.NewUpstreamHTTPS()`
+// But both of these cases miss out on a key feature from the stdlib:
+//     "The returned records are sorted by priority and randomized by weight within a priority."
+//     (https://golang.org/pkg/net/#Resolver.LookupSRV)
+// Does this matter? I don't know. It may someday. Let's use DoT so we don't need to worry about it.
+// See also: Go feature request for stdlib-supported DoH: https://github.com/golang/go/issues/27552
+var fallbackLookupSRV = lookupSRVWithDOT
+
+var friendlyDNSErrorLines = []string{
+	`Please try the following things to diagnose this issue:`,
+	`  1. ensure that argotunnel.com is returning "origintunneld" service records.`,
+	`     Run your system's equivalent of: dig srv _origintunneld._tcp.argotunnel.com`,
+	`  2. ensure that your DNS resolver is not returning compressed SRV records.`,
+	`     See GitHub issue https://github.com/golang/go/issues/27546`,
+	`     For example, you could use Cloudflare's 1.1.1.1 as your resolver:`,
+	`     https://developers.cloudflare.com/1.1.1.1/setting-up-1.1.1.1/`,
+}
+
+// EdgeDiscovery implements HA service discovery lookup.
+func edgeDiscovery(logger *logrus.Entry) ([][]*net.TCPAddr, error) {
+	_, addrs, err := netLookupSRV(srvService, srvProto, srvName)
+	if err != nil {
+		_, fallbackAddrs, fallbackErr := fallbackLookupSRV(srvService, srvProto, srvName)
+		if fallbackErr != nil || len(fallbackAddrs) == 0 {
+			// use the original DNS error `err` in messages, not `fallbackErr`
+			logger.Errorln("Error looking up Cloudflare edge IPs: the DNS query failed:", err)
+			for _, s := range friendlyDNSErrorLines {
+				logger.Errorln(s)
+			}
+			return nil, errors.Wrapf(err, "Could not lookup srv records on _%v._%v.%v", srvService, srvProto, srvName)
+		}
+		// Accept the fallback results and keep going
+		addrs = fallbackAddrs
+	}
+
+	var resolvedIPsPerCNAME [][]*net.TCPAddr
+	for _, addr := range addrs {
+		ips, err := resolveSRVToTCP(addr)
+		if err != nil {
+			return nil, err
+		}
+		resolvedIPsPerCNAME = append(resolvedIPsPerCNAME, ips)
+	}
+
+	return resolvedIPsPerCNAME, nil
+}
+
+func lookupSRVWithDOT(service, proto, name string) (cname string, addrs []*net.SRV, err error) {
+	// Inspiration: https://github.com/artyom/dot/blob/master/dot.go
+	r := &net.Resolver{
+		PreferGo: true,
+		Dial: func(ctx context.Context, _ string, _ string) (net.Conn, error) {
+			var dialer net.Dialer
+			conn, err := dialer.DialContext(ctx, "tcp", dotServerAddr)
+			if err != nil {
+				return nil, err
+			}
+			tlsConfig := &tls.Config{ServerName: dotServerName}
+			return tls.Client(conn, tlsConfig), nil
+		},
+	}
+	ctx, cancel := context.WithTimeout(context.Background(), dotTimeout)
+	defer cancel()
+	return r.LookupSRV(ctx, srvService, srvProto, srvName)
+}
+
+func resolveSRVToTCP(srv *net.SRV) ([]*net.TCPAddr, error) {
+	ips, err := netLookupIP(srv.Target)
+	if err != nil {
+		return nil, errors.Wrapf(err, "Couldn't resolve SRV record %v", srv)
+	}
+	if len(ips) == 0 {
+		return nil, fmt.Errorf("SRV record %v had no IPs", srv)
+	}
+	addrs := make([]*net.TCPAddr, len(ips))
+	for i, ip := range ips {
+		addrs[i] = &net.TCPAddr{IP: ip, Port: int(srv.Port)}
+	}
+	return addrs, nil
+}
+
+// ResolveAddrs resolves TCP address given a list of addresses. Address can be a hostname, however, it will return at most one
+// of the hostname's IP addresses
+func ResolveAddrs(addrs []string) ([]*net.TCPAddr, error) {
+	var tcpAddrs []*net.TCPAddr
+	for _, addr := range addrs {
+		tcpAddr, err := net.ResolveTCPAddr("tcp", addr)
+		if err != nil {
+			return nil, err
+		}
+		tcpAddrs = append(tcpAddrs, tcpAddr)
+	}
+	return tcpAddrs, nil
+}