During a summer not long ago, a client called with an urgent issue. Some critical messages were not being passed on, leading to a full stop on their end.

However I couldn't make heads or tails of what systems this was or how it related to us.

After a bit of back and forth, the customer said "ask Glenn, he always fixes this for us".

Glenn was of course on vacation and didn't respond to messages...

A few hours pass while we make zero progress on this issue and customer increasingly annoyed, when Glenn finally responds to my messages.

Turns out that on a different server from where our software is installed, there was a Java-based message broker service running that needed occasional kick in the pants (IIRC stopping, deleting a file, restarting). We're not a Java shop, we don't use message brokers.

For years, Glenn had been keeping this service running and updated for our customer, as the customer didn't have any internal resources that was capable of handling this. And nobody else at our shop knew this. Why? Well, he just did what had to be done and moved on to the next issue at hand, as he always did...