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.
debops.pki Ansible role provides support for the ACME protocol which is
used by default with the Let's Encrypt (there is a possibility to
integrate other similar services in the future). Interaction with the ACME
Certificate Authority is performed using the acme-tiny alternative client
written in Python.
To request and renew ACME certificates, a host needs to meet several requirements enforced by this Ansible role:
- A webserver configured to handle ACME challenges needs to be installed on the
host (currently this role supports only
http-01challenges). The debops.nginx role configures ACME support for all servers by default when other conditions are met.
- A publicly routable IPv4 or IPv6 address is required, so that the Certificate
Authority can contact the webserver and check the challenge responses. The
debops.pkirole detects if a suitable IP address is present, and disables the ACME support otherwise. This can be overridden if necessary for example to allow ACME on an internal server which can handle challenges forwarded through the gateway.
- Each domain or subdomain requested in a particular certificate needs to be correctly configured in the DNS to point to the host that requests the certificate. This is currently not done automatically and requires intervention by the administrator. If any domain specified in the request is not authorized by the correct ACME challenge, the certificate request won't be successful.
Due to above requirements, the default
domain PKI realm configured by the
role does not request ACME certificates automatically. Other realms created by
debops.pki role might have ACME support enabled, depending on presence
of a public IP address and a configured nginx server.
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.
To avoid triggering the limits too quickly due to a mistake,
disables the requests when the
acme/error.log file is present in the PKI
realm directory. You can check contents of this file to find out what might be
the issue, and after fixing it you need to remove the file to let the
pki-realm script make the request again.
How ACME certificates are managed¶
When a new PKI realm is created and support for ACME Certificate Authority is
enabled, a separate configuration for a Certificate Request will be created in
acme/ directory. This request does not use a wildcard certificate;
instead the default domain and a set of subdomains will be requested (see below
for configuration variables). The directory structure at this time looks like
/etc/pki/realms/ └── example.com/ ├── acme/ │ ├── account_key.pem │ ├── openssl.conf │ └── request.pem ├── config/ │ └── realm.conf ├── external/ ├── internal/ │ ├── gnutls.conf │ └── request.pem ├── private/ │ ├── key.pem │ └── realm_key.pem ├── public/ ├── CA.crt -> /etc/ssl/certs/ca-certificates.crt └── default.key -> private/key.pem
When the pki-realm detects the
acme/request.pem file, it
automatically calls the acme-tiny script using the
unprivileged account to request the certificate. When the request has completed
successfully and an
external/cert.pem certificate is found, the
certificate will be activated in the
public/ directory. The script
automatically downloads Let's Encrypt intermediate certificate as well as links
the Root CA certificate from the system certificate store provided by the
The realm directory after the process is complete:
/etc/pki/realms/ └── example.com/ ├── acme/ │ ├── account_key.pem │ ├── cert.pem │ ├── openssl.conf │ ├── intermediate.pem │ ├── request.pem │ └── root.pem -> /usr/share/ca-certificates/mozilla/DST_Root_CA_X3.crt ├── config/ │ └── realm.conf ├── external/ ├── internal/ │ ├── cert.pem │ ├── gnutls.conf │ ├── intermediate.pem │ ├── request.pem │ └── root.pem ├── private/ │ ├── key_chain_dhparam.pem │ ├── key_chain.pem │ ├── key.pem │ └── realm_key.pem ├── public/ │ ├── cert_intermediate_dhparam.pem │ ├── cert_intermediate.pem │ ├── cert.pem -> ../acme/cert.pem │ ├── cert.pem.sig │ ├── chain.pem -> cert_intermediate_dhparam.pem │ ├── intermediate_root.pem │ ├── root.pem -> ../acme/root.pem │ └── trusted.pem -> intermediate_root.pem ├── CA.crt -> public/trusted.pem ├── default.crt -> public/chain.pem ├── default.key -> private/key.pem ├── default.pem -> private/key_chain_dhparam.pem └── trusted.crt -> public/trusted.pem
If the request is not successful, you will find a
acme/error.log file with
log of the acme-tiny session. Check and fix the issue, and remove the log
file to re-enable the process again. Otherwise, pki-realm will not request
the certificates to avoid rate limit issues explained above.
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
Example: Certificate for apex domain and subdomains¶
In this example a X.509 certificate for the apex domain
going to be issued.
example.com will be listed in the certificate
The certificate will also be valid for the subdomains
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'
For testing it's strongly advised to uncomment
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
Example: Certificate for subdomains excluding the apex domain¶
In the example we create a certificate for
Subject) and for
mon.example.com (certificate Subject Alternative
Names), which does not include the
example.com apex 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'
ACME configuration variables¶
debops.pki role has several default variables which can be used to
control ACME support. The most important are:
- 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.
- 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
pki_acmeis set to
False, ACME support can be enabled independently in each PKI realm. By default, it is set to the same value as
- Name of the ACME Certificate Authority API endpoint to use. Dictionary with
endpoints is defined in the
pki_acme_ca_api_mapvariable. By default,
le-liveis used which points to the Let's Encrypt Live CA. For testing you can switch the default CA to
le-stagingwhich points to Let's Encrypt Staging CA.
- 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_subdomainsparameter. 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
can have several parameters related to the ACME certificates:
- 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.
- Boolean. Enable or disable ACME support per realm.
- 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.
- 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
- List of subdomains added to each apex (root) domain configured in the ACME certificate. Overrides list of default ACME subdomains.
- List of Distinguished Name entries which define the ACME certificate Subject.