housecarl/docs/jarl.md

Connecting Housecarl to Jarl

Housecarl uses Jarl, the BIND manager, for its DNS records. In this version that means one thing: the DNS-01 challenge for the web UI's certificate (certificates.md). Naming hosts in rules by their DNS names may use the same connection later.

Housecarl talks to Jarl's REST API with an API token. Give it a user of its own, with only the permission it needs.

1. A user for Housecarl, in Jarl

On the Jarl server, make a user without a password. It can't log in to Jarl's web UI, only use its tokens. Grant it the challenge record of Housecarl's own name, and nothing else:

jarl user create housecarl --no-password --comment "Housecarl on fw01" \
    --grant "records:write zones=adbraun.lol names=_acme-challenge.fw.adbraun.lol types=TXT"

Use your zone for adbraun.lol, and the name Housecarl's web UI is reached by for fw.adbraun.lol (tls.acme.domain). The grant lets the token add and remove TXT records at exactly _acme-challenge.fw.adbraun.lol:

• nothing else in the zone (names=);
• no other record type (types=TXT);
• no other zone (zones=).

It can see that the zone exists, which it needs to find it, but it can't read the zone's other records.

Why not something wider:

• Jarl's acme role (records:write names=_acme-challenge.* types=TXT) would let the token publish challenges for any name in any zone, and so obtain certificates for all of them. Housecarl needs only its own name.
• Your own account's token would carry all your permissions, and Housecarl's certificate would stop renewing the day your account changes. A user per program keeps the two apart, and the audit log shows housecarl/... for what Housecarl did.

If the challenge name is a CNAME into a zone kept for challenges, such as _acme-challenge.fw.adbraun.lol CNAME fw.acme.adbraun.lol., grant the target instead: zones=acme.adbraun.lol names=fw.acme.adbraun.lol.

2. The token

Make the token, and copy it to the Housecarl server into a file only the housecarl user can read:

jarl token create fw01 --user housecarl -q > housecarl.token          # on the Jarl server, or with the jarl CLI anywhere
scp housecarl.token fw01:
ssh fw01 'sudo install -m 0600 -o housecarl -g housecarl housecarl.token /etc/housecarl/jarl.token && rm housecarl.token'
rm housecarl.token

A token file is better than putting the token in housecarl.yaml: the configuration file is readable by the housecarl group, and gets copied around more readily.

You can give the token an expiry (--expires 365d). Rotate it in Jarl with jarl token rotate ID --grace 1d, then put the new secret in the file and restart housecarld within the grace period. Since the certificate is renewed every couple of months, nothing breaks while you do.

3. Housecarl's settings

In /etc/housecarl/housecarl.yaml:

jarl:
  server: https://dns.adbraun.lol:8053
  token_file: /etc/housecarl/jarl.token
  # ca_cert: /etc/housecarl/jarl-ca.pem   # if Jarl's certificate isn't from a public CA

Then restart housecarld (systemctl restart housecarl). Housecarl needs to reach Jarl's API over the network: Jarl's listen must include an address Housecarl can reach, ideally over HTTPS.

hc cert check (certificates.md) tests the connection, the token's permission, and that the record reaches the internet.