The Simpsons episode that explains legacy code problems
Original email from Dec 13, 2024
Do you remember that one Simpsons episode where Mr. Burns went to get a checkup?
In it, he discovers that he has every known disease known to man (yes, even juvenile diabetes). But by some miracle, they all magically cancel themselves out, kind of like this:
When this happens, whether you're Mr. Burns or, hypothetically speaking, a legacy codebase that has over 5 years of work done on it, well... it's REALLY hard to treat one problem without other ones popping up.
The same thing happened with my new water heater this week 😅
We installed a new one in my apartment, which (somehow?) caused the water pressure to INSTANTLY improve.
The water pressure was TOO good. It caused our shower head cap to fly off.
We investigated and realized... the screw used to keep the cap on was too short for the shower head. It was always too short. But this never happened before because there just wasn't enough pressure to cause it to pop off previously. So now we had to get a new screw to fix the issue.
And thus, my house was like Mr. Burns. Everything magically canceled itself out in perfect harmony... until I went in and improved something that needed fixing.
I bring this up because, in my experience, this happens ALL the time in code.
Something similar happened in our team a few months ago. For context: we manage one website that uses Nginx to redirect some URLs to an old version of the website. We got new orders to stop some of those redirections from happening.
This caused certain server-side functions that hadn't been run in years to start executing. Can you guess what happened next? 😄
Yup, when we did that, we realized things weren't working as expected. That old function ended up having a four-year-old bug that nobody ever detected because... it never ran!
This is why, quoting the very lines from that Simpsons episode, feels very fitting here...
MR. BURNS: So what you're saying is I'm indestructible.
DOCTOR: Oh, no, no. Even a slight breeze could–
MR. BURNS: Indestructible.
So yes, when you have a ton of problems that seem to "cancel" each other out, it can feel like it's indestructible.
Until you have to change something. Then it isn't.