What causes "Error looking up dns name [%v]: (%v)" in vitessio/vitess?

Verify the hostname resolves: `nslookup ` from the Vitess host; fix DNS or /etc/hosts if not

Error looking up dns name [%v]: (%v)

Error message

Error looking up dns name [%v]: (%v)

What it means

dnsLookup wraps net.LookupHost for DNSTracker. This error means the DNS query for the given hostname failed entirely — the resolver returned an error (NXDOMAIN, timeout, server failure) rather than an address list.

Source

Thrown at go/netutil/netutil.go:112

	// If the FQDN isn't returned by this function, check the order in the entry
	// in your /etc/hosts file.
	return strings.TrimSuffix(resolvedHostnames[0], "."), nil
}

// FullyQualifiedHostnameOrPanic is the same as FullyQualifiedHostname
// but panics in case of an error.
func FullyQualifiedHostnameOrPanic() string {
	hostname, err := FullyQualifiedHostname()
	if err != nil {
		panic(err)
	}
	return hostname
}

func dnsLookup(host string) ([]net.IP, error) {
	addrs, err := net.LookupHost(host)
	if err != nil {
		return nil, fmt.Errorf("Error looking up dns name [%v]: (%v)", host, err)
	}
	naddr := make([]net.IP, len(addrs))
	for i, a := range addrs {
		naddr[i] = net.ParseIP(a)
	}
	sort.Slice(naddr, func(i, j int) bool {
		return bytes.Compare(naddr[i], naddr[j]) < 0
	})
	return naddr, nil
}

// DNSTracker is a closure that persists state for
//
//	tracking changes in the DNS resolution of a target dns name
//	returns true if the DNS name resolution has changed
//	If there is a lookup problem, we pretend nothing has changed
func DNSTracker(host string) func() (bool, error) {
	dnsName := host

View on GitHub (pinned to 01a25a7d17)

Solutions

Verify the hostname resolves: `nslookup <host>` from the Vitess host; fix DNS or /etc/hosts if not
Remove stale entries pointing at deleted hosts from your topology/service discovery
Check resolver config (/etc/resolv.conf) and DNS server health
Restart/retry after DNS recovers — DNSTracker will keep failing until lookup succeeds

Example fix

// /etc/hosts, before
(stale or missing entry for vttablet-1)
// after
10.0.0.6 vttablet-1.example.com vttablet-1

Defensive patterns

Strategy: retry

Validate before calling

func hostResolvable(host string) error {
    _, err := net.LookupHost(host)
    return err // check before registering with DNSTracker
}

Try / catch

addrs, err := net.LookupHost(host)
if err != nil {
    // retry with backoff before giving up
    return retry.Do(func() error { _, err = net.LookupHost(host); return err })
}

Prevention

Verify DNS resolution of tablet hostnames before wiring them into DNSTracker
Monitor DNS server health; use local caching resolver (nscd/dnsmasq) with /etc/hosts fallback
Clean up service discovery entries when tablets are decommissioned

When it happens

Trigger: DNSTracker (or the anonymous refresh closure it builds) calls dnsLookup on a hostname that no longer resolves, or while the DNS resolver is down/timeouting during a checkAndRefreshDNS call.

Common situations: Tablet removed from DNS but still tracked; DNS server outage or network partition; typo in hostname used to construct connections; k8s service deleted while vtgate keeps its address.

Related errors

AI-assisted analysis of vitessio/vitess@01a25a7d17 (2026-09-01). Data as JSON: /api/errors/10147e2ad95f4c9c. Report an issue: GitHub.