DNS01

Configuring DNS01 Challenge Provider

This page contains details on the different options available on the Issuer resource’s DNS01 challenge solver configuration.

For more information on configuring ACME Issuers and their API format, read the ACME Issuers documentation.

DNS01 provider configuration must be specified on the Issuer resource, similar to the examples in the setting up documentation.

You can read about how the DNS01 challenge type works on the Let’s Encrypt challenge types page.

apiVersion: cert-manager.io/v1
kind: Issuer
metadata:
  name: example-issuer
spec:
  acme:
    email: user@example.com
    server: https://acme-staging-v02.api.letsencrypt.org/directory
    privateKeySecretRef:
      name: example-issuer-account-key
    solvers:
    - dns01:
        cloudDNS:
          project: my-project
          serviceAccountSecretRef:
            name: prod-clouddns-svc-acct-secret
            key: service-account.json

Each issuer can specify multiple different DNS01 challenge providers, and it is also possible to have multiple instances of the same DNS provider on a single Issuer (e.g. two CloudDNS accounts could be set, each with their own name).

For more information on utilizing multiple solver types on a single Issuer, read the multiple-solver-types section.

Setting Nameservers for DNS01 Self Check

cert-manager will check the correct DNS records exist before attempting a DNS01 challenge. By default cert-manager will use the recursive nameservers taken from /etc/resolv.conf to query for the authoritative nameservers, which it will then query directly to verify the DNS records exist.

If this is not desired (for example with multiple authoritative nameservers or split-horizon DNS), the cert-manager controller exposes two flags that allows you alter this behavior:

--dns01-recursive-nameservers Comma separated string with host and port of the recursive nameservers cert-manager should query.

--dns01-recursive-nameservers-only Forces cert-manager to only use the recursive nameservers for verification. Enabling this option could cause the DNS01 self check to take longer due to caching performed by the recursive nameservers.

Example usage:

--dns01-recursive-nameservers-only --dns01-recursive-nameservers="8.8.8.8:53,1.1.1.1:53"

If you’re using the cert-manager helm chart, you can set recursive nameservers through .Values.extraArgs or at the command at helm install/upgrade time with --set:

--set 'extraArgs={--dns01-recursive-nameservers-only,--dns01-recursive-nameservers=8.8.8.8:53\,1.1.1.1:53}'

Delegated Domains for DNS01

By default, cert-manager will not follow CNAME records pointing to subdomains.

If granting cert-manager access to the root DNS zone is not desired, then the _acme-challenge.example.com subdomain can instead be delegated to some other, less privileged domain (less-privileged.example.org). This could be achieved in the following way. Say, one has two zones:

  • example.com
  • less-privileged.example.org
  1. Create a CNAME record pointing to this less privileged domain:
_acme-challenge.example.com	IN	CNAME	_acme-challenge.less-privileged.example.org.
  1. Grant cert-manager rights to update less privileged less-privileged.example.org zone

  2. Provide configuration/credentials for updating this less privileged zone and add an additional field into the relevant dns01 solver. Note that selector field is still working for the original example.com, while credentials are provided for less-privileged.example.org

apiVersion: cert-manager.io/v1
kind: Issuer
metadata:
  ...
spec:
  acme:
    ...
    solvers:
    - selector:
        dnsZones:
        - 'example.com'
    - dns01:
        # Valid values are None and Follow
        cnameStrategy: Follow
        route53:
          region: eu-central-1
          accessKeyID: <Access ID for less-privileged.example.org here>
          hostedZoneID: <Zone ID for less-privileged.example.org here>
          secretAccessKeySecretRef:
            ...

If you have a multitude of (sub)domains requiring separate certificates, it is possible to share an aliased less-privileged domain. To achieve it one should create a CNAME record for each (sub)domain like this:

_acme-challenge.example.com	    IN	CNAME	_acme-challenge.less-privileged.example.org.
_acme-challenge.www.example.com	IN	CNAME	_acme-challenge.less-privileged.example.org.
_acme-challenge.foo.example.com	IN	CNAME	_acme-challenge.less-privileged.example.org.
_acme-challenge.bar.example.com	IN	CNAME	_acme-challenge.less-privileged.example.org.

With this configuration cert-manager will follow CNAME records recursively in order to determine which DNS zone to update during DNS01 challenges.

Supported DNS01 providers

A number of different DNS providers are supported for the ACME Issuer. Below is a listing of available providers, their .yaml configurations, along with additional Kubernetes and provider specific notes regarding their usage.

Webhook

cert-manager also supports out of tree DNS providers using an external webhook. Links to these supported providers along with their documentation are below:

You can find more information on how to configure webhook providers here.

To create a new unsupported DNS provider, follow the development documentation here.

Last modified July 12, 2021 : Add BizflyCloud Cert-manager webhook (29092df)