backends changing shouldn't be very likely, but services may well change. we
should restart sshguard from nixos-rebuild instead of merely plopping down a new
config file and waiting for the user to restart sshguard.
The current module assumes use of iptables and breaks if nftables is
used instead.
This change configures the correct backend based on the
config.networking.nftables.enable setting.
The fix for #62874 introduced a race condition on startup: the postStart
commands that configure the firewall run concurrently with sshguard's
creation of the ipsets that the rules depend on. Unfortunately iptables
fails hard when referencing an ipset that doesn't exist, so this causes
non-deterministic crashlooping until sshguard wins the race.
This change fixes that race condition by always creating the ipset and
reconfiguring the firewall before starting sshguard, so that the order
of operations is always deterministic.
This change also cleans up the ipsets on sshguard shutdown, so that
removing sshguard from a running system doesn't leave state behind.
Fixes#65985.
Upstream switched to a different type of ipset table, whereas we
create ipset in post-start which overrides upstream, and renders
sshguard ineffective.
Remove ipset creation from post-start, and let it get automatically
by upstream script (sshg-fw-ipset) as part of startup
1. Allow syslog identifiers with special characters
2. Do not write a pid file as we are running in foreground anyway
3. Clean up the module for readability
Without this, when deploying using nixops, restarting sshguard would make
nixops show an error about restarting the service although the service is
actually being restarted.
