housecarl/docs/operations.md

Running Housecarl

The services

systemctl status housecarl          # housecarld: the API, the web UI, the log
journalctl -u housecarl -f
systemctl reload housecarl          # reread the TLS certificate
systemctl status housecarl-ruleset  # the ruleset loaded at boot

The firewall itself is the kernel's: it stays in force while housecarld is stopped, restarted or upgraded. Without housecarld there is no API, no web UI, no log and no probation timer.

housecarld logs each change it applies, rollbacks, and what it couldn't apply. When it starts, it applies the configuration again (rolling back first what was on probation when it stopped).

Reviewing before applying

In the web UI, edits are collected as pending changes (the bar under the header), and Changes shows them with the diff of the ruleset; Apply puts them in force together. The switch in the header (Review edits / Live edits) applies each edit at once instead. With hc, see cli.md.

Changes on probation

Changes made over the network roll back unless confirmed (design.md). The web UI and hc confirm their own changes once they reach Housecarl again over a new connection, so normally nothing waits:

$ hc rule add input --from admins --service ssh
created rule input #31
applied and confirmed (history 12): this client reached Housecarl again over a new connection

A change that cuts the client off can't be confirmed that way:

applied on probation (history 13), but couldn't confirm it: … context deadline exceeded
It is rolled back within 1m50s unless confirmed ('hc confirm')

By hand (with --no-confirm, or with Settings → "a person confirms each change"):

hc status              # Probation: 2 changes roll back in 97s unless confirmed
hc confirm
hc rollback            # or undo them now

The web UI shows a banner with a countdown and both buttons. A rollback is in the history, as an undo by housecarl via rollback, so it can be undone like any change.

If you are cut off by a change: wait. When the time is up, the previous ruleset comes back by itself. If you are cut off by a confirmed change, use the console, or SSH from a source the rules still let in:

sudo hc history list
sudo hc history undo 42

The ruleset at boot

A confirmed ruleset (or one changed through the socket) is saved to /var/lib/housecarl/ruleset.nft, which housecarl-ruleset.service loads before the network comes up, so before PPPoE, WireGuard or DHCP bring up their interfaces. To see what would load:

sudo cat /var/lib/housecarl/ruleset.nft
sudo nft -c -f /var/lib/housecarl/ruleset.nft     # check it

Dynamic sets start empty after a reboot. The saved ruleset has no flowtable, since its devices may not exist yet: housecarld adds it when it starts, and whenever a flowtable device appears (flowtable.md).

If the ruleset fails to load at boot

Should ruleset.nft fail to load (a damaged file, an nftables or kernel upgrade that refuses something in it), the machine would otherwise boot with no firewall at all until housecarld starts. Instead, housecarl-ruleset.service loads a fallback that housecarld saves beside it, /var/lib/housecarl/ruleset-fallback.nft, from the same confirmed configuration:

• Nothing new gets in from the external zones' interfaces, to the firewall or through it: no port forwards, no SSH or web UI from the internet.
• What the firewall and the inside need to keep working is let in: established connections, the ICMPv6 IPv6 needs (neighbour discovery, router advertisements, packet too big), and DHCPv6 replies from link-local addresses.
• Everything else is let through: the LAN, WireGuard and the firewall itself are reachable from the inside, so you can log in and fix it.
• IPv4 leaving an external zone is masqueraded (when any source NAT is configured), so the inside still reaches the internet. MSS clamping stays, if it is on.

PPPoE itself isn't affected: its discovery and session are Ethernet frames, and the PPP link's negotiation happens before any IP, neither of which an inet table sees.

The fallback only knows which interfaces face the internet from the zones marked external. With none, it lets nothing but loopback through, and the warning no_external_zone says so.

When the fallback loads, the unit is marked failed, and the journal says why (as a critical message):

systemctl status housecarl-ruleset
journalctl -b -u housecarl-ruleset

housecarld puts the real ruleset back when it starts, and saves a fresh ruleset.nft. If it can't apply it either, the fallback stays in force: hc status and the dashboard say "NOT in force: the boot fallback is in force", and /healthz answers 503 (Monitoring). Fix what hc status or the journal reports, then restart housecarld.

Keep Debian's nftables.service disabled (systemctl disable nftables, without --now): at boot it loads /etc/nftables.conf, and stopping or restarting it runs nft flush ruleset, which deletes every table, Housecarl's included. housecarl-ruleset.service runs after it at boot, which covers the ordinary case, but not a restart of nftables.service later. Housecarl never reads or writes /etc/nftables.conf; its ruleset is saved in /var/lib/housecarl/ruleset.nft. The dashboard and hc status warn while nftables.service is enabled.

Other programs' tables are left alone: fail2ban's (inet f2b-table), Docker's, Incus's. Housecarl replaces only its own table, so they keep their rules through every Housecarl change and restart, and nothing needs restarting in a particular order. A packet must get past every table on its hook, so a drop in any of them wins.

Hits

Every rule, NAT rule, built-in and policy has a counter. hc rule list, hc forward list and the web UI show packets; hc counters shows them all, with bytes. They count from housecarld's start, and carry across changes to the ruleset.

Quotas

hc quotas (and the rules page) show what each quota used and when it resets; hc rule reset-quota ID starts one again. housecarld resets quotas at midnight when their period ends (late, if it was stopped then), and saves their usage every five minutes and when it stops; after a reboot it puts it back. A reboot without a clean stop loses at most the last five minutes' count.

The log

Rules with --log (Log in the web UI) and, with hc settings set --log-drops on, what the input and forward policies drop (at most 10 packets a second) are logged:

hc log -f
hc log --search 198.51.100.7

10:02:13  hc input #95 drop:     wan  -   198.51.100.7:53868 -> 203.0.113.10:22   tcp syn
10:02:15  hc forward policy drop: wan  eth1  198.51.100.9:443 -> 192.168.1.20:51432  tcp

The packets go to netlink log group 4171, where housecarld reads them; the last 2000 are kept in memory. They aren't written to the kernel log or the journal. A rule's log isn't rate-limited: on a busy rule, give it a limit, or log only new connections (--state new).

Connections

The built-in that accepts established connections lets their packets through without checking the rules again: a rule added later doesn't stop a connection already open. Traffic → Connections (hc connections) lists what the kernel tracks, with NAT (to 192.168.1.10:443: a port forward; as 203.0.113.10: masqueraded) and the time left:

hc connections --search 192.168.1.50
hc connections --search ":443 tcp"
hc connections close --search 192.168.1.50

Closing a connection deletes its tracking entry: its next packet is checked by the rules as they are now. One they block is stopped; one they allow carries on (TCP connections are picked up again mid-stream).

To make a block stop open connections by itself, tick "every packet" on the rule (--every-packet): it is checked before established connections are accepted, like rules with a quota (rules.md).

Tracing

Traffic → Trace (hc trace) follows packets through the whole ruleset: Housecarl's rules and every other table (Docker's, fail2ban's, an old inet main), each rule and policy they meet, and what accepted or dropped them:

$ hc trace --address 192.168.1.50 --port 443 --seconds 60
14:02:13.120  192.168.1.50:51432 -> 198.51.100.9:443  tcp syn in eth1 out wan
    inet housecarl forward: built-in: mss-clamp -> continue
    inet housecarl forward: rule forward #12 (kids at night) -> drop
    => DROPPED by rule forward #12 (kids at night)

It traces packets from or to the address, on the port (either way), for 5 to 600 seconds, at most 200 packets and 20 a second. It works with nftables' own tracing: a table of its own (inet housecarl-trace, hooked before everything else) marks the packets, and nft monitor trace reports them; the table goes when the trace ends. One trace runs at a time.

When something doesn't get through

1. Trace it (above): it names the rule or policy that dropped it, in whichever table.
2. hc log -f with --log-drops on: is it dropped by a policy (no rule accepted it), or by a rule (its number is in the line)?
3. hc rule list forward (or input): hits on the rule you expect?
4. hc ruleset: the rule as nftables sees it, with the zones' interfaces and the sets' families.
5. hc status: other tables. A Docker or Incus table, or an old one, can drop what Housecarl accepts.
6. Port forwards: hc forward list hits, and the inside host's own firewall and default route (answers must go back through Housecarl).

Backups

housecarl-backup.timer runs housecarld backup daily. It writes a consistent copy of the database to backup.dir (/var/backups/housecarl/housecarl-<time>.db), and deletes those older than backup.retention (30 days), keeping at least backup.keep_at_least (7). A backup holds everything: configuration, history, users, tokens (hashed) and the audit log.

sudo -u housecarl housecarld backup                 # now
sudo -u housecarl housecarld backup /tmp/h.db       # to a file of your choice
sudo systemctl disable --now housecarl-backup.timer # no daily backups

To restore, stop housecarld first; restore refuses to replace the database under it:

sudo systemctl stop housecarl
sudo -u housecarl housecarld restore /var/backups/housecarl/housecarl-20261014T020000Z.db
sudo systemctl start housecarl

housecarld applies the restored configuration when it starts. The old database is kept next to it as housecarl.db.before-restore-<time>.

Upgrades

apt upgrade restarts a running housecarld. A new version upgrades the database when it starts, and an older one refuses a database a newer one has upgraded: restore a backup to go back.

Monitoring

GET /healthz needs no login, and answers within a few seconds of any change (it reads the ruleset at most every five seconds, however often it is asked):

$ curl -s https://firewall.example.net:8070/healthz
{"ok":true,"version":"0.1.0","firewall":"applied","probation":0,"warnings":[]}

Field
ok	true with HTTP 200 when the firewall is as it should be; false with HTTP 503 otherwise
firewall	applied (Housecarl's ruleset is in force), unconfigured (nothing configured yet, so nothing to apply), fallback (the boot fallback is in force), missing (no Housecarl table: flushed, or never applied)
probation	changes waiting to be confirmed, rolled back unless they are
warnings	codes of problems with the machine, as hc status shows them (nftables_service)

For Checkmk, an HTTP check on the URL that expects status 200 (and, if you like, the string "firewall":"applied") covers housecarld being down, the fallback and a missing ruleset. Reach it from where the input rules let the monitor in (a rule for the Checkmk server's address and port 8070).

Checks

housecarld check validates the configuration in the database against this machine's interfaces, the same checks as hc status shows (validation.md).