Restart nginx and/or uwsgi whenever PostgreSQL is updated

[jwodder]

Currently, the deployment pins the PostgreSQL package to prevent unattended security updates, as updating PostgreSQL causes it to restart, breaking Wheelodex's database connection. This is obviously sub-optimal.

Possible resolution: Configure systemd to restart nginx and/or uwsgi whenever PostgreSQL is restarted. In addition, configure unattended upgrades to not run while Wheelodex jobs are running (Use systemd's Conflicts field?).

• It seems the only way to prevent two systemd timer services from running at the same time without causing one of them to fail is to use the flock command.
  • Problem: unattended-upgrades is run as root, and the wheelodex jobs are run as the wheelodex user, so there will likely be permission errors if they both have the same lockfile.

Look into other possible resolutions, as well.