For Google at least the SRE teams for infrastructure components are not large, neither in total nor relative to the huge infrastructure that they are managing.

For Google at least the SRE teams for infrastructure components are not large, neither in total nor relative to the huge infrastructure that they are managing. You could call this operational scalability, it is made possible by decoupling service quality from individual pieces of hardware. The key ingredient are redundancy across relatively large failure domains and auto mated handling of all foreseeable events. Everything is built around this concept, compute with a fault-tolerant container scheduler, storage on a fault-tolerant file system, checksuming everywhere,... Another enabler is probably keeping things simple at the component level.