micro/go-micro · error

could not determine host IP addresses for %s

Error message

could not determine host IP addresses for %s

What it means

When no IPs are supplied, NewMDNSService attempts net.LookupIP on the hostname (or hostname+domain as a fallback) to discover A/AAAA records. If that lookup fails, this error reports that no IP addresses could be determined for the host, so A records cannot be published.

Source

Thrown at internal/util/mdns/zone.go:108

		}
		hostName = fmt.Sprintf("%s.", hostName)
	}
	if err := validateFQDN(hostName); err != nil {
		return nil, fmt.Errorf("hostName %q is not a fully-qualified domain name: %v", hostName, err)
	}

	if len(ips) == 0 {
		var err error
		ips, err = net.LookupIP(trimDot(hostName))
		if err != nil {
			// Try appending the host domain suffix and lookup again
			// (required for Linux-based hosts)
			tmpHostName := fmt.Sprintf("%s%s", hostName, domain)

			ips, err = net.LookupIP(trimDot(tmpHostName))

			if err != nil {
				return nil, fmt.Errorf("could not determine host IP addresses for %s", hostName)
			}
		}
	}
	for _, ip := range ips {
		if ip.To4() == nil && ip.To16() == nil {
			return nil, fmt.Errorf("invalid IP address in IPs list: %v", ip)
		}
	}

	return &MDNSService{
		Instance:     instance,
		Service:      service,
		Domain:       domain,
		HostName:     hostName,
		Port:         port,
		IPs:          ips,
		TXT:          txt,
		TTL:          defaultTTL,

View on GitHub (pinned to 24529f1404)

Solutions

1. Pass an explicit ips slice (e.g. discovered interface addresses) so no lookup is performed: net.InterfaceAddrs() filtered to IPNet addresses
2. Ensure the machine's hostname resolves: add it to /etc/hosts or configure DNS
3. Check network/DNS configuration on the host; the wrapped lookup must succeed for auto-discovery

Example fix

// before
svc, err := NewMDNSService("myapp", "_http._tcp", "local.", "", 8080, nil, nil) // lookup fails offline
// after
var ips []net.IP
if addrs, err := net.InterfaceAddrs(); err == nil {
	for _, a := range addrs {
		if ipnet, ok := a.(*net.IPNet); ok && !ipnet.IP.IsLoopback() {
			ips = append(ips, ipnet.IP)
		}
	}
}
svc, err2 := NewMDNSService("myapp", "_http._tcp", "local.", "", 8080, ips, nil)

func localIPs() []net.IP {
	var ips []net.IP
	if addrs, err := net.InterfaceAddrs(); err == nil {
		for _, a := range addrs {
			if ipnet, ok := a.(*net.IPNet); ok && !ipnet.IP.IsLoopback() {
				ips = append(ips, ipnet.IP)
			}
		}
	}
	return ips // pass explicitly to skip DNS lookup
}

func hasUsableIPs(ips []net.IP) bool {
	return len(ips) > 0
}

svc, err := NewMDNSService(instance, service, domain, hostName, port, ips, txt)
if err != nil {
	if strings.Contains(err.Error(), "could not determine host IP addresses") {
		// offline host: fall back to explicit interface addresses or skip registration
		return fmt.Errorf("pass explicit IPs or fix DNS/hosts resolution: %w", err)
	}
	return err
}

When it happens

Trigger: Calling NewMDNSService(instance, service, domain, hostName, port, nil/[], txt) on a machine where DNS/mDNS resolution of its own hostname fails — no resolver configured, hostname not in /etc/hosts, or the host has no network interfaces.

Common situations: Offline or air-gapped machines; containers whose hostname isn't resolvable; freshly provisioned VMs before /etc/hosts is populated; VPN-only environments where the lookup path is broken.

Related errors

• invalid IP address in IPs list: %v
• ErrIPNotFound
• failed to bind to any unicast udp port
• failed to bind to any multicast udp port
• failed to join multicast group on all interfaces

AI-assisted analysis of micro/go-micro@24529f1404 (2026-09-01). Data as JSON: /api/errors/f959a484815c662c. Report an issue: GitHub.