What causes "DNSName not set on AliasTarget" in kubernetes/kops?

Inspect the Route53 record and set the correct AliasTarget DNSName (the NLB's dns name)

DNSName not set on AliasTarget

Error message

DNSName not set on AliasTarget

What it means

findNetworkLoadBalancerByAlias matches an ELBv2 Alias target (e.g. from a Route53 record) against existing NLBs by DNS name. If alias.DNSName is empty after trimming a trailing dot, the function cannot match anything and returns "DNSName not set on AliasTarget".

Solutions

Inspect the Route53 record and set the correct AliasTarget DNSName (the NLB's dns name)
If the record is broken/unwanted, delete or recreate the alias record with a valid target
Re-run kops update once the alias record carries a DNSName

Example fix

// before (alias target)
{ HostedZoneId: "Z..." } // DNSName missing
// after
{ HostedZoneId: "Z...", DNSName: "k8s-elb-xxx.elb.us-east-1.amazonaws.com" }

Defensive patterns

Strategy: validation

Validate before calling

if alias != nil && (alias.DNSName == nil || strings.TrimSuffix(aws.ToString(alias.DNSName), ".") == "") {
    return fmt.Errorf("route53 alias target has no DNSName; fix the record before update")
}

Type guard

func aliasHasDNSName(a *route53types.AliasTarget) bool {
    return a != nil && strings.TrimSuffix(aws.ToString(a.DNSName), ".") != ""
}

Prevention

Inspect Route53 alias records before applying cluster changes
Never create alias records programmatically without DNSName
Audit manually edited DNS records in the cluster hosted zone

When it happens

Trigger: Called from findDNSTargetNLB when a Route53 A/AAAA alias record's AliasTarget has a nil or empty DNSName field while kOps tries to determine whether the record already points at an NLB.

Common situations: Corrupt or manually edited Route53 alias record; record built programmatically with DNSName omitted; AWS SDK change exposing nil DNSName on an alias target.

Related errors

AI-assisted analysis of kubernetes/kops@4c8573c808 (2026-09-05). Data as JSON: /api/errors/86f3f0fe9db6deb5. Report an issue: GitHub.

Appendix: source

Thrown at upup/pkg/fi/cloudup/awstasks/network_load_balancer.go:113

var _ fi.CompareWithID = (*NetworkLoadBalancer)(nil)
var _ fi.CloudupTaskNormalize = (*NetworkLoadBalancer)(nil)
var _ fi.CloudupProducesDeletions = (*NetworkLoadBalancer)(nil)

func (e *NetworkLoadBalancer) CompareWithID() *string {
	return e.Name
}

func findNetworkLoadBalancerByAlias(cloud awsup.AWSCloud, alias *route53types.AliasTarget) (*elbv2types.LoadBalancer, error) {
	ctx := context.TODO()

	// TODO: Any way to avoid listing all NLBs?
	request := &elbv2.DescribeLoadBalancersInput{}

	dnsName := aws.ToString(alias.DNSName)
	matchDnsName := strings.TrimSuffix(dnsName, ".")
	if matchDnsName == "" {
		return nil, fmt.Errorf("DNSName not set on AliasTarget")
	}

	matchHostedZoneId := aws.ToString(alias.HostedZoneId)

	found, err := describeNetworkLoadBalancers(ctx, cloud, request, func(lb elbv2types.LoadBalancer) bool {
		if matchHostedZoneId != aws.ToString(lb.CanonicalHostedZoneId) {
			return false
		}

		lbDnsName := aws.ToString(lb.DNSName)
		lbDnsName = strings.TrimSuffix(lbDnsName, ".")
		return lbDnsName == matchDnsName || "dualstack."+lbDnsName == matchDnsName
	})
	if err != nil {
		return nil, fmt.Errorf("error listing NLBs: %v", err)
	}

	if len(found) == 0 {

View on GitHub (pinned to 4c8573c808)