Downtime, Backups, and IPv6
Sorry for the unexpected downtime that lasted a few days and affected all the services here. One of the hard drives in the raid on my server suddenly showing miserable I/O performance, since the other drive was fine according to tests, SMART and logs I decided to take the slow drive offline to have it replaced. That turned out fatal since the other drive was also kaput and all my virtual machines on that server were now corrupted.
On the bright side the 2nd MX server worked fine and held all the email like it supposed to do until I got the main server back up and running (yaay to “exim -Mvb” to at least be able to read important mails that are in the mail server queue).
Long story short, since these drives have caused me much trouble in the past too, I decided to just get a new server with different hardware and restore everything from backups. Like any sysadmin I have my regular backups and scripts to check that they are working and occasionally test them to ensure I can restore a server from backups, but I’ve never had to really actually restore everything from a backup on one of my private servers. So when doing so I noticed minor things that aren’t perfect and needed to be changed to make my life easier in the future and decided to share my experience.
Backups. Instead of making one large archive with all the directories backed up (e.g. /etc, /home, /opt, …), split it up into multiple archives of the applications you are backing up (e.g. /etc/apache2, /var/www/). I should have known better since this is common practice at work. It makes your life a lot easier when restoring from a backup if you have one archive with everything in it associated to a specific application, Digging through a backup of /etc and trying to remember all sub-directories needed to get email back up and running was a chore (webinterface, greylisting, spamassassin, exim, dovecot … some of them store data you also want to restore in other parts of the filesystem). You can always tar all the application backups together into one package before uploading it to the backup server if you want.
Use some kind of configuration and/or deployment management software (Puppet, Chef, Ansible, Salt, own scripts, …). Don’t underestimate how relaxing it is to just press a button to get your server(s) back into the defined state you previously had, just drop in the data from the backups (configuration too depending on how you roll) and you are good to go. Getting networking up and running manually took me longer than it should have (VPN networks, routing on the VM host, sysctl settings, NAT, which interfaces are bridged, which are internal, guest network configuration, …), I’ve put that all into Ansible playbooks now so it’s just a press of a button.
IPv6 is still sorely underused in the internet. I always set it up on all my hosts and mainly I see it being used by core services like email servers, dns, package download servers of large distributions, sometimes ntp, that kind of stuff, not so much on normal websites. Ordering extra IPv4 IPs for my guests normally takes an extra day or so until they are assigned to me (and they each cost extra), so I do enjoy having a huge subnet ip IPv6 IPs free of charge to do with as I please. It’s nice to spin up a virtual server, assign it an IPv6 IP and have it online without having to worry about NAT or port forwarding or other stuff you are confronted with when getting a server/services online that reside on an internal IP.
While I like to push people to embrace IPv6 early and get used to it, it is also important to give it the same attention you give IPv4 to make sure that you aren’t opening yourself up to security problems. Make sure you have the same firewall policy for IPv6 as you do for IPv4 and IPv6 brings a few new features with it that IPv4 didn’t have. Unless you explicitly need/use them it is best to shut them off. Below I’ll ad some IPv6 settings you probably want to set per default unless you are explicitly using them.