The Wall = Ouch!
The Wall, a somewhat quirky album by Pink Floyd, great in parts and so-so in others followed up by a seminal film (movie) and now after that mild digression, I shall move to what I wanted to really say here, of course I do very much appreciate music.
The Wall, in web applications, is that perfect storm of occurrences that suddenly and within seconds brings a web application to it's knees and it is almost always caused by one thing, a stacking up of all available application threads, which to be fair, is preceded, rather quickly, with a slow down in performance. There can be many reasons, a successful marketing campaign, a major event, an unexpectedly successful launch yet whatever the cause it is possible to architect and build infrastructure that can cope with any load and this is how.
- Test all web site code, successfully; unit-test, integration-test, regression-test, load-test* and until code passes these tests it should not go into production, at all.
- *Accurately estimate what the anticipated load will be, the number of users, establish a required-baseline performance number, for instance all requests must complete with 4 seconds, and load-test until you achieve that number with 150% of the anticipated load. If the web application(s) passes these tests and more traffic than even the 150% you tested to arrives and you hit The Wall, then it is not the infrastructure or web application which is at fault, but the estimate of anticipated load.
I will make one more controversial statement here, anyone who cannot afford $'s to go through these sorts of tests, effectively and completely, should not be offering any sort of service to others, which they wish to make money from. Imagine buying a car only to find it continuously fails eventually injuring or killing others.