kubernetes/kops · error

failed to create certificate: %w

Error message

failed to create certificate: %w

What it means

BuildChallengeServerCertificate wraps an error from x509.CreateCertificate when self-signing the challenge server certificate. Given the key was already generated, failures here stem from invalid template fields or crypto-layer problems (e.g. bad issuer/subject key pairing or invalid validity).

Source

Thrown at pkg/bootstrap/challenge.go:87

	template := x509.Certificate{
		SerialNumber: big.NewInt(1),
		Subject: pkix.Name{
			CommonName: serverName,
		},
		NotBefore: notBefore,
		NotAfter:  notAfter,

		KeyUsage:              keyUsage,
		ExtKeyUsage:           []x509.ExtKeyUsage{x509.ExtKeyUsageServerAuth},
		BasicConstraintsValid: true,
	}

	template.DNSNames = append(template.DNSNames, serverName)

	der, err := x509.CreateCertificate(cryptorand.Reader, &template, &template, privateKey.Key.Public(), privateKey.Key)
	if err != nil {
		return nil, fmt.Errorf("failed to create certificate: %w", err)
	}

	parsed, err := x509.ParseCertificate(der)
	if err != nil {
		return nil, fmt.Errorf("failed to parse certificate: %w", err)
	}
	tlsCertificate := &tls.Certificate{
		PrivateKey:  privateKey.Key,
		Certificate: [][]byte{parsed.Raw},
		Leaf:        parsed,
	}

	return tlsCertificate, nil
}

View on GitHub (pinned to 4c8573c808)

Solutions

1. Inspect the wrapped error message (%w chain) for the exact x509 cause
2. Verify the template: publicKey matches the signer's private key and DNSNames includes the challenge server hostname
3. Confirm the host clock is sane (notBefore = now-15min; huge clock skew can produce invalid validity windows)
4. Upgrade kops — stock code paths rarely fail here; a custom patch may have broken the template

cert, err := BuildChallengeServerCertificate(clusterName)
if err != nil {
  return fmt.Errorf("challenge server startup failed: %w", err)
}

When it happens

Trigger: NewChallengeServer triggers certificate creation; x509.CreateCertificate(cryptorand.Reader, &template, &template, privateKey.Key.Public(), privateKey.Key) returns an error, e.g. template fields (SerialNumber, DNSNames, KeyUsage) constructed inconsistently or an internal RSA/ECDSA mismatch.

Common situations: Bugs introduced when editing the certificate template; platform crypto restrictions; time-related issues if notBefore/notAfter logic is changed; extremely rare in stock kops since the template is fixed.

Understand the failure class

• SSL/TLS and certificate errors — how TLS handshakes and certificate validation fail.

Related errors

• failed to parse certificate: %w
• error creating certificate: %w
• parsing key: %v
• error issuing certificate: %v
• error loading certificate pool

AI-assisted analysis of kubernetes/kops@4c8573c808 (2026-09-05). Data as JSON: /api/errors/1bc6e114a5e9cb90. Report an issue: GitHub.