One thing everything needs

Think of it when a drawing of a system has one box that every arrow points to, or only one person knows how something works.

In everyday life

A house where every light, the fridge and the heating run through one fuse. Ten new lamps do not help when that one fuse blows.

One case

A food delivery app runs 12 app servers, and all of them store orders in one database. At 19:30 on a Friday the database’s disk fills up. All 12 servers are healthy, and nobody can order for 50 minutes.

One thing everything needs
The ideaHow things break
One thing everything needs

One part that everything else needs, with no backup. When it breaks, the whole system stops, however healthy the rest is.

How things break, Foundations

Every case

More copies of the easy parts do not help if they all lean on one hard part: one database, one network link, one password, one person who knows how to deploy. Systems grow these points quietly, because one is simpler and cheaper than two. You find them by asking of each part: “what happens if this disappears right now?”

The word

Engineers call this

single point of failureOne part that everything else needs, with no backup. When it breaks, the whole system stops, however healthy the rest is.

Find the part that everything needs. Give it a backup, or make sure the rest can carry on without it for a while.

Where this idea leads