A website on every address steps aside for websites that name an address on the same port

The wildcard then listens on the machine's other addresses only, in the built-in proxy and in Traefik,
and follows the machine when it gains or loses an address.

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

blacktip.go

@@ -114,6 +114,7 @@ type Blacktip struct {
 	logq       chan model.LogEntry
 	reportMu   sync.Mutex
 	updating   atomic.Bool
+	addrSig    string // machine addresses a wildcard website was spread across, "" when none was
 	updateMsg  string // outcome of the update Hammerhead asked for, reported back
 	updateID   string // the request that updateMsg answers
 	updStage   string // progress of the running update, reported to Hammerhead
@@ -247,6 +248,50 @@ func (b *Blacktip) fetchConfig(ctx context.Context) (*model.EdgeConfig, error) {
 	return &cfg, json.NewDecoder(resp.Body).Decode(&cfg)
 }
 
+// hostIPv4 lists every IPv4 address on this machine, loopback included: what a wildcard bind covers.
+func hostIPv4() []string {
+	var ips []string
+	addrs, _ := net.InterfaceAddrs()
+	for _, a := range addrs {
+		if ipn, ok := a.(*net.IPNet); ok && ipn.IP.To4() != nil {
+			ips = append(ips, ipn.IP.String())
+		}
+	}
+	sort.Strings(ips)
+	return ips
+}
+
+// bindIPs says which addresses a mapping listens on. Normally that is its own BindIP. A website on
+// 0.0.0.0 steps aside for websites of the same kind that name an address on the same port: it then
+// listens on the machine's other addresses only, so a wildcard never takes a port from a specific IP.
+func bindIPs(m model.Mapping, all []model.Mapping) []string {
+	if !model.Web(m.Proto) {
+		return []string{m.BindIP}
+	}
+	if ip := net.ParseIP(m.BindIP); ip == nil || !ip.IsUnspecified() {
+		return []string{m.BindIP}
+	}
+	named := map[string]bool{}
+	for _, o := range all {
+		if o.ID == m.ID || o.Proto != m.Proto || o.Port != m.Port {
+			continue
+		}
+		if ip := net.ParseIP(o.BindIP); ip != nil && !ip.IsUnspecified() {
+			named[ip.String()] = true
+		}
+	}
+	if len(named) == 0 {
+		return []string{m.BindIP}
+	}
+	var out []string
+	for _, ip := range hostIPv4() {
+		if !named[ip] {
+			out = append(out, ip)
+		}
+	}
+	return out
+}
+
 func listenKey(m model.Mapping) string {
 	n := "tcp"
 	if m.Proto == model.ProtoUDP {
@@ -311,23 +356,27 @@ func (b *Blacktip) apply(cfg *model.EdgeConfig) {
 			continue
 		}
 		// a range opens one listener per port; each shifts the target port by its offset
-		for p := m.Port; p <= m.LastPort(); p++ {
-			mm := m
-			mm.Port = p
-			k := listenKey(mm)
-			if want[k] == nil {
-				want[k] = &bindSet{off: p - m.Port}
+		for _, ip := range bindIPs(m, cfg.Mappings) {
+			for p := m.Port; p <= m.LastPort(); p++ {
+				mm := m
+				mm.BindIP, mm.Port = ip, p
+				k := listenKey(mm)
+				if want[k] == nil {
+					want[k] = &bindSet{off: p - m.Port}
+				}
+				want[k].ms = append(want[k].ms, b.maps[m.ID])
 			}
-			want[k].ms = append(want[k].ms, b.maps[m.ID])
 		}
 	}
 	// https ports can also answer on :80 with a redirect, unless something else owns that port
 	redirects := map[string][]*mapState{}
 	for _, m := range cfg.Mappings {
 		if b.tr == nil && m.Proto == model.ProtoHTTPS && m.RedirectHTTP {
-			k := "tcp|" + net.JoinHostPort(m.BindIP, "80")
-			if _, taken := want[k]; !taken {
-				redirects[k] = append(redirects[k], b.maps[m.ID])
+			for _, ip := range bindIPs(m, cfg.Mappings) {
+				k := "tcp|" + net.JoinHostPort(ip, "80")
+				if _, taken := want[k]; !taken {
+					redirects[k] = append(redirects[k], b.maps[m.ID])
+				}
 			}
 		}
 	}
@@ -340,6 +389,13 @@ func (b *Blacktip) apply(cfg *model.EdgeConfig) {
 			delete(b.listeners, k)
 		}
 	}
+	b.addrSig = ""
+	for _, m := range cfg.Mappings {
+		if ips := bindIPs(m, cfg.Mappings); len(ips) != 1 || ips[0] != m.BindIP {
+			b.addrSig = strings.Join(hostIPv4(), ",")
+			break
+		}
+	}
 	b.status = map[string]string{}
 	bring := func(k string, ms []*mapState, off int, redirect bool) {
 		if l, ok := b.listeners[k]; ok {
@@ -349,7 +405,9 @@ func (b *Blacktip) apply(cfg *model.EdgeConfig) {
 			l.close()
 			delete(b.listeners, k)
 		}
-		l, err := b.open(ms, off, redirect)
+		_, addr, _ := strings.Cut(k, "|")
+		host, _, _ := net.SplitHostPort(addr)
+		l, err := b.open(host, ms, off, redirect)
 		if err != nil {
 			log.Printf("open %s: %v", k, err)
 			if !redirect {
@@ -376,7 +434,11 @@ func (b *Blacktip) apply(cfg *model.EdgeConfig) {
 		bring(k, ms, 0, true)
 	}
 	if b.tr != nil {
-		b.tr.sync(b.ctx, webMaps, cfg.AcmeEmail, cfg.AcmeStages)
+		binds := map[string][]string{}
+		for _, ms := range webMaps {
+			binds[ms.m.ID] = bindIPs(ms.m, cfg.Mappings)
+		}
+		b.tr.sync(b.ctx, webMaps, binds, cfg.AcmeEmail, cfg.AcmeStages)
 		if e := b.tr.err(); e != "" {
 			for _, ms := range webMaps {
 				b.status[ms.m.ID] = e
@@ -585,10 +647,25 @@ func (b *Blacktip) reportLoop(ctx context.Context) {
 			return
 		case <-t.C:
 			b.report()
+			b.recheckAddresses()
 		}
 	}
 }
 
+// recheckAddresses re-applies the config when this machine gains or loses an address that a wildcard
+// website is spread across, so the listeners follow the machine.
+func (b *Blacktip) recheckAddresses() {
+	b.mu.Lock()
+	last, sig := b.last, b.addrSig
+	b.mu.Unlock()
+	if last == nil || sig == "" {
+		return
+	}
+	if strings.Join(hostIPv4(), ",") != sig {
+		b.apply(last)
+	}
+}
+
 // ---------- access logs ----------
 
 func (b *Blacktip) logAccess(e model.LogEntry) {