Cattle, not pets
Pets have names and go to the vet. Cattle have numbers and get replaced. Your servers should be cattle.
The metaphor was coined by Bill Baker at Microsoft and spread by Randy Bias around 2012. A pet is the server with a name from Norse mythology that has been hand-configured over years, that nobody dares reboot, and whose rebuild nobody can any longer describe. Cattle are numbered instances created from a template, replaced at the first sign of trouble and never repaired.
The entire modern operations model assumes the latter: autoscaling, immutable infrastructure, rolling updates and container orchestration only work if an individual instance is expendable. The nuance usually forgotten is that not everything can be cattle — state has to live somewhere, and that database is still a pet, however well cared for.