ACME Integration

Automated Certificate Management Environment (ACME) is a protocol that allows automated certificate requests, retrieval of certificates and certificate renewal. It was designed to enable easy deployment of X.509 certificates from Let's Encrypt.

The debops.pki Ansible role provides support for the ACMEv2 protocol which is used by default with the Let's Encrypt. Many Certificate Authorities have added support for the ACMEv2 protocol; therefore, the role may work with them as well. Interaction with the ACME Certificate Authority is performed using the Python-based acme-tiny client for HTTP challenges and the certbot client for DNS challenges.

Let's Encrypt rate limits

The Let's Encrypt ACME Certificate Authority has different rate limits related to the number of certificate requests and the number of domains permitted per certificate.

Certificate renewal

The debops.pki role creates a cron entry for the pki-realm script to be executed periodically for all realms. When a realm has the ACME configuration active, it will check for validity of the certificate, and about a month before the expiration date it will try to renew the certificate automatically.

Example: Certificate for apex domain and subdomains

The apex domain is the "root" level of your domain. In this example a X.509 certificate for the apex domain example.com is going to be issued. example.com will be listed in the certificate Subject DN. The certificate will also be valid for the subdomains www.example.com, blog.example.com and mail.example.com which are included in the certificate as Subject Alternative Names.

pki_realms:
  - name: 'example.com'
    acme: True
    acme_subdomains: [ 'www', 'blog', 'mail' ]
    # acme_ca: 'le-staging-v2'

For testing it's strongly advised to uncomment acme_ca with le-staging-v2 to use the staging environment of Let's Encrypt. It does not create a trusted certificate and allows you to avoid problems with the rate limits in the production environment. When you are sure that everything works correctly, comment the staging environment out again to get yourself a valid and trusted X.509 certificate.

Example: Certificate for subdomains excluding the apex domain

In the example we create a certificate for logs.example.com (certificate Subject) and for mon.example.com (certificate Subject Alternative Names), which does not include the example.com apex (root) domain.

pki_realms:
  - name: 'logs.example.com'
    acme: True
    acme_default_subdomains: []
    # Can also include different domains like 'mail.example.org'
    # in the same realm.
    acme_domains: [ 'mon.example.com' ]
    # acme_ca: 'le-staging-v2'

Again, for testing it's strongly advised to uncomment acme_ca: le-staging-v2. See above for details.

ACME configuration variables

The debops.pki role has several default variables which can be used to control ACME support. The most important are:

pki_acme: Boolean. When True, support for ACME Certificate Authority will be configured for all PKI realms unless disabled on the realm level. By default the role checks if a public IP address is available and a default domain is configured, otherwise the support is disabled automatically.
pki_acme_install: Boolean. Enable or disable installation of acme-tiny and configuration of ACME support without enabling it for all realms. When this variable is set to True and pki_acme is set to False, ACME support can be enabled independently in each PKI realm. By default, it is set to the same value as pki_acme.
pki_acme_ca: Name of the ACME Certificate Authority API endpoint to use. Dictionary with endpoints is defined in the pki_acme_ca_api_map variable. By default, le-live-v2 is used which points to the Let's Encrypt Live CA. For testing you can switch the default CA to le-staging-v2 which points to Let's Encrypt Staging CA.
pki_acme_default_subdomains: List of subdomains which will be added to the default ACME domain and all other domains configured for ACME certificate by default, can be overridden by item.acme_subdomains parameter. By default, the www. subdomain will be added to each domain configured in the realm. Remember that all subdomains need to be correctly configured in the DNS for the Certificate Authority to sign the request.

Each PKI realm configured in the pki_realms or pki_*_realms variables can have several parameters related to the ACME certificates:

item.name: Name of the PKI realm. If it has at least one dot, the realm name will be treated as the apex (root) domain to configure for this realm.
item.acme: Boolean. Enable or disable ACME support per realm.
item.acme_domains: List of additional apex (root) domains to add in ACME Certificate Signing Request. Each domain will have the default or custom subdomains added to it.
item.acme_default_subdomains: List of subdomains that should be added to all of the ACME apex (root) domains. If you want to create an ACME certificate only with the apex domain, you might need to set this parameter to an empty list using [] to override pki_acme_default_subdomains.
item.acme_subdomains: List of subdomains added to each apex (root) domain configured in the ACME certificate. Overrides list of default ACME subdomains.
item.acme_subject: List of Distinguished Name entries which define the ACME certificate Subject.