[er_d0s]

I’ve tried c4/plantuml (and loved the concept) but have never been able to make it stick, it always seems to get out of date quickly and having a feeling of “I’m not sure if this is up to date” is worse than no documentation at all (because you need to learn the documentation, then the behaviour). Honestly the fastest way I’ve found to understand large distributed systems is by observing the interactions between them, schema detection in service bus type architecture and tools like X-ray (in aws) or open tracing give you a good picture of “this thing produces or consumes this type of message”

For individual systems I think a good inversion of control/dependency injection system can give you a good overview of the connections between components.

If I’m stepping into a giant ball of spaghetti code I generally set the debugger at line 1 and start stepping, and draw a lot of boxes and lines as I go… then throw those drawings away when I’m done. They’re really only helpful while you’re producing them (like taking notes as you read a textbook), hopefully in that situation you improve the code as you go so this approach isn’t as necessary!