When is the right time to introduce high availability for web site?
There are many articles on High Availability options.
It’s not that obvious however WHEN is the right time to switch from single server to high availability configuration.
Please consider my situation:
http://www.postjobfree.com is 24/7 web site with significant traffic:
http://www.similarweb.com/website/postjobfree.com
Currently I run it on a single server: both IIS 7.0 web server and SQL Server 2008 run on the same hardware box.
There is occasional (~one per month) ~5 minutes downtime usually caused by reboot required by some Windows Server update. Usually downtime is scheduled and happens at night. Still it’s unpleasant, because Google Bot and some users are still active at night.
Current web site revenue is at ~$8K/month.
I consider switching to two-servers configuration (web farm of 2 web servers and cluster of 2 SQL Servers hosted on two hardware servers).
Pros:
1) High Availability (theoretically no downtime). Even if one of servers goes down – another server would take over.
2) No data loss: without SQL cluster, up to one day of data can be lost in case of hardware failure (we do daily backup).
Cons:
1) More effort to setup and maintain such configuration.
2) Higher hosting cost. Instead of ~$600/month it would be about $1200/month.
What would be your recommendation?
Best Answer
Short answer: When down time or the risk of it costs you more than it would cost you to have high availability.
It is fundamentally an economic decision. As an example. $8k/month implies that an outage of 2 hours will cost you $22. If you can configure your system such that you can go from scratch to a fully functional site in 2 hours, then high availability would only gain you $22 of functionality above that.
Put another way, you can save money unless / until you have 54 hours of unpreventable down-time in a given month.