If the remote address configuration for strongSwan is not valid when the
Proton VPN watchdog starts, it will now regenerate it immediately. This
can happen, for example, if the Internet has been down for a while, and
the watchdog has iterated through all of the servers in the cache.
Restarting the service will now force it to reconfigure the tunnel and
bring the VPN back up.
Occasionally, ProtonVPN servers randomly reject the EAP authentication
credentials. When this happens, the tunnel fails and is not restarted
automatically by strongSwan. As such, the watchdog needs to react to
this event as well.
One major problem with the current DNS-over-VPN implementation is that
the ProtonVPN servers are prone to random outages. When the server
we're using goes down, there is not a straightforward way to switch to
another one. At first I tried creating a fake DNS zone with A records
for each ProtonVPN server, all for the same name. This ultimately did
not work, but I am not sure I understand why. strongSwan would
correctly resolve the name each time it tried to connect, and send IKE
initialization requests to a different address each time, but would
reject the responses from all except the first address it used. The
only way to get it working again was to restart the daemon.
Since strongSwan is apparently not going to be able to handle this kind
of fallback on its own, I decided to write a script to do it externally.
Enter `protonvpn-watchdog.py`. This script reads the syslog messages
from strongSwan (via the systemd journal, using `journalctl`'s JSON
output) and reacts when it receives the "giving up after X tries"
message. This message indicates that strongSwan has lost connection to
the current server and has not been able to reestablish it within the
retry period. When this happens, the script will consult the cached
list of ProtonVPN servers and find the next one available. It keeps
track of the ones that have failed in the past, and will not connect to
them again, so as not to simply bounce back-and-forth between two
(possibly dead) servers. Approximately every hour, it will attempt to
refresh the server list, to ensure that the most accurate server scores
and availability are known.
Dustin