It all depends…
Omar Shahine wrote a great article entitled Designing for Services Dependencies. If you’re involved in IT at all this is a must read, no matter whether you’re a developer or on the operations side.
If only more developers would understand the dependencies they add into their systems!
Here’s a quick chart that talks about “The Nines”. You’ll hear people talking about wanting to have “five nines” of availability. Good luck with that! 🙂
|Reliability||Downtime / year|