Frequently Asked Questions (FAQ)

On this page you will find answers to some frequently asked questions about cert-manager.

Terminology

What does publicly trusted and self-signed mean?

These terms are defined in the TLS Terminology page.

What do the terms root, intermediate and leaf certificate mean?

These terms are defined in the TLS Terminology page.

Certificates

Can I trigger a renewal from cert-manager at will?

This is a feature in cert-manager starting in v0.16 using the cmctl CLI. More information can be found on the renew command's page

When do certs get re-issued?

To determine if a certificate needs to be re-issued, cert-manager looks at the the spec of Certificate resource and latest CertificateRequests as well as the data in Secret containing the X.509 certificate.

The issuance process will always get triggered if the:

  • Secret named on Certificate's spec, does not exist, is missing private key or certificate data or contains corrupt data
  • private key stored in the Secret does not match the private key spec on Certificate
  • public key of the issued certificate does not match the private key stored in the Secret
  • cert-manager issuer annotations on the Secret do not match the issuer specified on the Certificate
  • DNS names, IP addresses, URLS or email addresses on the issued certificate do not match those on the Certificate spec
  • certificate needs to be renewed (because it has expired or the renewal time is now or in the past)
  • certificate has been marked for renewal manually using cmctl

Additionally, if the latest CertificateRequest for the Certificate is found, cert-manager will also re-issue if:

  • the common name on the CSR found on the CertificateRequest does not match that on the Certificate spec
  • the subject fields on the CSR found on the CertificateRequest do not match the subject fields of the Certificate spec
  • the duration on the CertificateRequest does not match the duration on the Certificate spec
  • isCA field value on the Certificate spec does not match that on the CertificateRequest
  • the DNS names, IP addresses, URLS or email addresses on the CertificateRequest spec do not match those on the Certificate spec
  • key usages on the CertificateRequest spec do not match those on the Certificate spec

Note that for certain fields re-issuance on change gets triggered only if there is a CertificateRequest that cert-manager can use to determine whether Certificate's spec has changed since the previous issuance. This is because some issuers may not respect the requested values for these fields, so we cannot rely on the values in the issued X.509 certificates. One such field is .spec.duration- change to this field will only trigger re-issuance if there is a CertificateRequest to compare with. In case where you need to re-issue, but re-issuance does not get triggered automatically due to there being no CertificateRequest (i.e after backup and restore), you can use cmctl renew to trigger it manually.

Why isn't my root certificate in my issued Secret's tls.crt?

Occasionally, people work with systems which have made a flawed choice regarding TLS chains. The TLS spec has the following section for the "Server Certificate" section of the TLS handshake:

This is a sequence (chain) of certificates. The sender's certificate MUST come first in the list. Each following certificate MUST directly certify the one preceding it. Because certificate validation requires that root keys be distributed independently, the self-signed certificate that specifies the root certificate authority MAY be omitted from the chain, under the assumption that the remote end must already possess it in order to validate it in any case.

In a standard, secure and correctly configured TLS environment, adding a root certificate to the chain is almost always unnecessary and wasteful.

There are two ways that a certificate can be trusted:

  • explicitly, by including it in a trust store.
  • through a signature, by following the certificate's chain back up to an explicitly trusted certificate.

Crucially, root certificates are by definition self-signed and they cannot be validated through a signature.

As such, if we have a client trying to validate the certificate chain sent by the server, the client must already have the root before the connection is started. If the client already has the root, there was no point in it being sent by the server!

The same logic with not sending root certificates applies for servers trying to validate client certificates; the same justification is given in the TLS RFC.

cert-manager publishes all events to the Kubernetes events mechanism, you can get the events for your specific resources using kubectl describe <resource> <name>.

Due to the nature of the Kubernetes event mechanism these will be purged after a while. If you're using a dedicated logging system it might be able or is already also storing Kubernetes events.

What happens if issuance fails? Will it be retried?

cert-manager will retry a failed issuance except for a few rare edge cases where manual intervention is needed.

If an issuance fails because of a temporary error, it will be retried again with a short exponential backoff (currently 5 seconds to 5 minutes). A temporary error is one that does not result in a failed CertificateRequest.

If the issuance fails with an error that resulted in a failed CertificateRequest, it will be retried with a longer binary exponential backoff (1 hour to 32 hours) to avoid overwhelming external services.

You can always trigger immediate renewal using the cmctl renew command

Is ECC (elliptic-curve cryptography) supported?

cert-manager supports ECDSA key pairs! You can set your certificate to use ECDSA in the privateKey part of your Certificate resource.

For example:

apiVersion: cert-manager.io/v1
kind: Certificate
metadata:
name: ecdsa
spec:
secretName: ecdsa-cert
isCA: false
privateKey:
algorithm: ECDSA
size: 256
dnsNames:
- ecdsa.example.com
issuerRef:
[...]

If renewBefore or duration is not defined, what will be the default value?

Default duration is 90 days. If renewBefore has not been set, Certificate will be renewed 2/3 through its actual duration.

Miscellaneous

Kubernetes has a builtin CertificateSigningRequest API. Why not use that?

Kubernetes has a Certificate Signing Requests API, and a kubectl certificates command which allows you to approve certificate signing requests and have them signed by the certificate authority (CA) of the Kubernetes cluster.

This API and CLI have occasionally been misused to sign certificates for use by non-control-plane Pods but this is a mistake. For the security of the Kubernetes cluster, it is important to limit access to the Kubernetes certificate authority, and it is important that you do not use that certificate authority to sign certificates which are used outside of the control-plane, because such certificates increase the opportunity for attacks on the Kubernetes API server.

In Kubernetes 1.19 the Certificate Signing Requests API has reached V1 and it can be used more generally by following (or automating) the Request Signing Process.

cert-manager currently has some limited experimental support for this resource.

How to write "cert-manager"

cert-manager should always be written in lowercase. Even when it would normally be capitalized such as in titles or at the start of sentences. A hyphen should always be used between the words, don't replace it with a space and don't remove it.