For an introduction to the ACME protocol and its DNS verification part, you can refer to our beta release blog post.
Agnos is a single-binary program allowing you to easily obtain certificates (including wildcards) from Let's Encrypt using DNS-01 challenges. It answers Let's Encrypt DNS queries on its own, bypassing the need for API calls to your DNS provider.
DNS-01 is summarized by Let's Encrypt documentation as such:
- You can use this challenge to issue certificates containing wildcard domain names.
- It works well even if you have multiple web servers.
- Keeping API credentials on your web server is risky.
- Your DNS provider might not offer an API.
- Your DNS API may not provide information on propagation times.
By serving its own DNS answers, agnos:
- Nullify the need for API and API credentials
- Nullify all concerns regarding propagation times
Hence, agnos removes virtually all downsides of dns-01 challenges.
Agnos leverages let's encrypt capability to follow DNS
NS records. It requires you to add to your DNS zone:
AAAA) record pointing to the public-facing IP address of the server on which agnos will run. On this server, UDP port 53 (the one used by DNS) should be open and free.
- For each domain you will want to validate, an
NSrecord for the corresponding
_acme-challengesub-domain, indicating that agnos should be used as a name server for this specific domain.
These instructions are given for a Linux system but a similar process will likely work on all Unixes, and maybe windows.
Pre-compiled binaries for Linux/amd64 are available for every tagged release. Be aware that they are statically built using musl and vendoring their own openssl so that they can easily be installed even on older distributions.
Agnos is available in the AUR. You can install it using:
yay -S agnos.
Agnos is written in Rust. To build it you will need to have the rust toolchain installed, in a version greater or equal to 1.65.0. On most distributions, this should be done using rustup.
Once you have obtained the source, the following command will build the binaries and put them in the root directory of the repo.
or more explicitly:
cargo build --locked --bins --release
ln target/release/agnos agnos
ln target/release/agnos-generate-accounts-keys agnos-generate-accounts-keys
Because agnos listen on the low-numbered port 53, it requires special privileges. Running it as root will do, but if you (understandably) don't want to do that, the following command is for you:
# as root
setcap 'cap_net_bind_service=+ep' agnos
# agnos is the file of the binary as compiled above
Let's Encrypt accounts are identified by an e-mail address and a private RSA key. To generate such a key, use the following command:
openssl genrsa 2048 > /path/to/store/the/key.pem
or if you prefer a larger key:
openssl genrsa 4096 > /path/to/store/the/key.pem
Alternatively, you can use the provided
agnos-generate-accounts-keys binary to automatically generate private keys for the accounts listed in the configuration file.
agnos-generate-accounts-keys --key-size 4096 your_config.toml
It is advised to use absolute rather than relative paths in the configuration file.
There are three "levels" in the configuration:
The general configuration level is where the IP address to listen on is provided.
dns_listen_addr = "188.8.131.52:53"
Several Let's Encrypt accounts can be specified. For each account, an e-mail address and the path to the account RSA private key must be provided.
private_key_path = "priv_key.pem"
For each account, several certificates can be ordered. Each certificate can cover multiple domains. On disk, a certificate is represented by two files: the full certificate chain, and the private key of the certificate (generated by agnos and different from the account private key).
In the configuration file,
accounts.certificates is a TOML array of tables meaning that several certificates can be attached to one account by writing them one after the other.
# A first certificate ordered for that account.
domains = ["doma.in","*.doma.in"]
fullchain_output_file = "fullchain_A.pem"
key_output_file = "cert_key_A.pem"
# A second certificate ordered for that account.
domains = ["examp.le","another.examp.le","and.a.completely.different.one"]
fullchain_output_file = "fullchain_B.pem"
key_output_file = "cert_key_B.pem"
Say that we have the following domains we want to obtain a certificate (or multiple certificates) for:
- its wildcard variant:
Notice here that we are not requesting a certificate for
*.examp.le but only for one subdomain:
Let's encrypt DNS-01 challenge is going to ask for TXT DNS records on the following three domains:
doma.inand its wildcard)
Let's assume that agnos is going to run on a server whose public-facing IP address is
184.108.40.206. The goal is to indicate that the three
_acme_challenge domains cited above are managed by agnos using
NS DNS records.
NS records usually point to domain names, so we will also set an
A record on
agnos-ns.doma.in to point to
agnos-ns.doma.in is entirely arbitrary, it could be another, completely independent domain, you control, like
We create the following records:
In the zone of
agnos-ns.doma.in A 220.127.116.11
_acme-challenge.doma.in NS agnos-ns.doma.in
In the zone of
_acme-challenge.examp.le NS agnos-ns.doma.in
_acme-challenge.another.examp.le NS agnos-ns.doma.in
Note: Though it may seem cumbersome, this must only be done once from your DNS provider web interface. Once it is done, you will never have to touch a
agnos takes a single command line argument, the path to its configuration file, and two optional flags:
--no-staging to use Let's Encrypt production server, and
--debug to display more debug information. Help is available via
When running, it checks whether the certificates of the full chain are going to expire in the next 30 days, and only renew them in that case, so it is suitable to be used in a cron job.
A systemd unit and timers are provided in the
systemd folder of this repo.
PRs and issues are very welcome.
Build using usual
The Makefile is for integration testing in a docker-compose. At the root, run
sudo make compose (sudo is required to use docker) to test agnos using pebble.