Introduction

You’ve just inherited a “mission critical” service, with:

• A thousand-line function last touched in 2013.

• Three mystery cron jobs nobody dares disable.

• A Postgres schema diagram that looks like a bowl of spaghetti.

Congrats ... you’re now the keeper of the legacy monster.

Most engineers’ first instinct is to burn it down and rewrite it. But that almost always fails.

John knows this. He doesn’t panic at a 10,000-line utils.py. He just puts on his archaeologist hat and starts making careful moves. Of course, he never writes down what those moves are (because then you wouldn’t need him). You, on the other hand, will write it down. 

In this module, we’ll cover the 3 best practices you’ll need for navigating legacy code: 

• Triage first

• Safe changes

• Migration plan

Let’s get started!