Priorities for high-availability hosting
So if you want your web site and e-mail to work all the time, what’s the solution? In my view, the priorities are these:
- Choose a reliable host. Shared hosting (whether single-server or clustered) is relatively cheap and finding a good quality hosting company doesn’t require spending a fortune. I expect uptime to be around 99.9% over a prolonged period – good hosts will be able to demonstrate a record of achieving this. Or if you’re looking for the best possible reliability and money is no object, get a fully-managed dedicated server (this eliminates one major source of problems – your fellow users!)
- Choose a second reliable host. One in a different datacenter a long distance away from the first (another continent is good!). Use both hosts to provide dns and mail services for your domain – nameserver and mail-exchanger records allow for this so that if one is unreachable the other will be used automatically.
- Plan for the worst-case scenario. What would you do if the server died and the backups were found to be corrupt? Or if the server got hacked and your site defaced, with backups being replaced by the modified pages? Sure it shouldn’t happen but it does. So keep your own backups (multiple copies), synchronize them to another host and check that they are good.
Will all that give you 100% uptime? No. The main limitation is dns propagation time – using failover you can update your nameservers almost instantly to point to your spare server but dns servers around the world will not update until their cached data expires. And while you can set a short TTL (time to live) on your records there’s no guarantee that all ISPs will respect it, in fact it’s pretty much guaranteed that some won’t!
So I regard dns failover to a hot-spare server as a rather imperfect emergency measure in the event of disaster or prolonged outage. But in that situation, you will be glad you have it!