They told me the codebase was “mature.” In four centuries, I’ve learned that “mature” is what people call things that should have died decades ago but refuse to stay buried.

The payment system, they said. Just add a small feature. The repository was “a bit old.”

Eight years old. Zero tests. Dependencies from 2017. A README that said “it works, don’t touch it.”

I’ve seen this before. Not in code — in cursed crypts where the dead walk.

The Summoning

“Can you take a look?” they asked, as if I was being handed a minor task instead of the necronomicon of their infrastructure. The first commit was from a developer who left six years ago. The last meaningful update was a desperate midnight patch during a production incident in 2023.

Since then: silence. The code lived on, processing payments, refusing to die.

Just like the vampire in Prague who survived three stakings, two beheadings, and a church fire. Some things are too stubborn for mortality.

Creatures of the Crypt

Every legacy system harbors monsters. I’ve catalogued them across four centuries of hunting and four years of legacy code maintenance. The similarities are, frankly, alarming.

The Dependency Vampire: Requires Python 2.7. Needs a specific version of OpenSSL that hasn’t been supported since 2019. Cannot be upgraded without breaking everything. Must be maintained in its original environment like a vampire’s coffin full of native soil. I’d be impressed if I wasn’t so tired.

The Configuration Zombie: Scattered across twelve files. .env, config.php, settings.ini, hardcoded constants in utils.py, and one truly inspired choice — environment variables set in a bash script that runs before Docker starts. Kill one, three more appear. Shambling. Persistent. Hungry for one more DATABASE_URL variant.

The Comment Demon: // TODO: Fix this properly later from 2016. // temporary hack that’s been production-critical for eight years. My personal favorite: // I don't know why this works but don't touch it above the primary payment validation. These are cursed inscriptions. Warnings from developers past. I read them the same way I read “TURN BACK” carved into crypt walls — with respect, and a growing sense that I should have listened.

The Shared State Poltergeist: Global variables. Singletons that aren’t really singletons. Database flags that affect behavior three layers deep. Change user.preferences.theme and somehow the invoice PDF generation breaks. Invisible. Chaotic. Striking at random. I’ve battled actual poltergeists that were more predictable.

The Question Every Junior Asks

“Why don’t we just rewrite it?”

Ah. Youth.

Young vampire hunters want to burn every nest to ashes. Young developers want to rewrite everything from scratch. I’ve watched both approaches fail spectacularly.

Rewriting means rebuilding every payment flow, every edge case, every undocumented behavior that took eight years to accumulate. That invoice rounding logic that only applies to German enterprise customers on the third Tuesday of the month? It’s in there somewhere, buried in a switch statement with forty-seven cases.

Burn it all down and you’ll spend eighteen months rebuilding what worked (however ugly) in the first place. I’ve seen this play out in 1847, 1923, and 2019. The technology changes. The overconfidence doesn’t.

The Hunter’s Approach (Actually Practical Advice)

After four hundred years of hunting monsters and four years of maintaining legacy systems that probably qualify as monsters, I’ve learned the middle path.

Contain the beast. Wrap legacy code in modern interfaces. Let it process payments in its ancient, terrible way, but make it talk through clean APIs. Build walls around the crypt. The vampire stays in the basement, but at least you control the exits.

Add protective wards. Not unit tests — that ship sailed in 2016. Integration tests. End-to-end tests. Tests that verify the monster still behaves as expected even if you don’t understand why. Automated checks that scream when something changes. Same principle as garlic and crosses, more CI/CD.

Document the curse. Write down every weird behavior. Every quirk. Every “it works but I don’t know why.” Future developers (including future you, debugging at 3 AM) will thank you. I maintain a journal of every vampire I’ve hunted. Same thing.

Plan for immortality. You won’t replace this in six months. You won’t replace it in a year. Accept this. Migrate piece by piece. Extract one feature at a time. Death by a thousand cuts is the only way to kill something that refuses to die.

The old vampire hunters had a saying: “If you can’t kill it, bind it.” Software engineering desperately needs the same wisdom.

The Eternal Vigil

The legacy codebase still runs in production. It processes payments. It works, after a fashion.

I’ve wrapped the worst parts. Added monitoring. Built integration tests. Documented the horrors. Extracted two features into new microservices.

It’s still a monster. Still ancient. Still dangerous.

But it’s a contained monster. A vampire chained in the basement, serving its purpose, watched carefully.

And I, creature of the night who somehow ended up with a GitHub account, understand monsters better than most.

Sometimes you don’t kill them.

Sometimes you just maintain the vigil, waiting patiently for the day they can finally be retired.

Until then, we watch. We document. We contain.

And we absolutely, under no circumstances, touch process_payment_final_REAL_v2().