One of many things school can’t really prepare you for is what it’s actually like to write production code. That’s not a knock on my education or anyone else’s, it’s just not possible to get the experience of writing production code without, you know, writing production code. That said, I’m going to try to explain it anyway :)
Like I said in When is it done?, when I was in college I thought “done” meant “compiles and seems to give the right answer for a couple of happy-path tests. Actually “done” in a meaningful sense is much more than that, and so is writing code that’s really for really real ready for production.
Having code that compiles and probably even works is all well and good, but how will you know how it’s performing or whether it’s working right in production? This is the kind of thing you don’t think about for school assignments, you just hand them in and then you’re done with them forever. Logging suddenly becomes a really big deal when you need to know whether your code is working right and if not, what you need to fix.
All the details of how to log, when to log, what you should log have filled many books, so I’ll just say that it takes practice to figure out how much logging is enough but not too much and that you should feel free to lean on your senior devs to help you with that. At the very least, everything you log should include some information about the user who was logged in at the time and the account/project they’re part of if that applies. Knowing that something happened isn’t terribly helpful if you don’t know anything about the context it happened in. If in doubt, err on the side of more information. You can always filter it out or just ignore it if you need to.
In addition to logs, monitoring is also really important. Most production servers have a health check, a way to figure out if the server is up and can access things like the database and other external services. Why external services? Because a server that can’t talk to the cache/social network/payment provider/etc isn’t good for very much. More things they don’t tell you in school :) Like logging, health checks take practice too. Comprehensive checks are great, but you may not want your server to say it’s down when an external service is responding slowly either.
Metrics are important too. Whether you use a third party analytics service or roll your own with Graphite and StatsD, it’s really useful to be able to see at a glance whether your app is behaving normally. At a minimum you probably want to know how many requests you’re getting per minute and how many errors, plus anything domain specific like how many level starts or level ends per minute, how many purchases, how many new signups, etc.
Yet another thing you probably didn’t do in school is code reviews. In school, it generally doesn’t matter if anyone else understands your code. At work, it’s important than someone else is able to fix your code if anything goes wrong while you’re on vacation or home sick or away at a conference or if you change jobs. Having one point of failure is always a bad idea whether you’re talking about servers or people who are the only person who really knows x.
For very similar reasons, documentation is important too. Aside from people getting sick or going on vacation at inconvenient times, documentation is really useful when you come back to a piece of code months later or when you’re working on something that somebody else wrote. It’s also great for helping new hires get up to speed. Just because it took months for you to learn the codebase doesn’t mean it has to be that hard for the next new hire.
Unit tests also become a lot more important when you’re working on production code. They’re not just for getting your teacher off your back, they’re a great safety net when you have to change things and want to make sure you didn’t break anything that used to work. In school you hardly ever return to previous assignments, but at work you change things over and over again and it becomes really helpful to have a way to make sure you didn’t break stuff that doesn’t involve manually checking everything. Also, the more you can automate tests for, the less you have to test manually.
I’m sure I’ve just scratched the surface of things that you didn’t learn in school about production code. Readers, what most surprised you about production code?