Borg

Borg is Google's internal cluster management system, a predecessor to Kubernetes that orchestrates the allocation of compute resources across Google's planetary-scale infrastructure. Borg manages fault tolerance, resource isolation, and job scheduling for the thousands of services that constitute Google's production environment, from web search to BigQuery query execution to Gmail delivery. Its design philosophy — declarative job specification, centralized scheduling, and the reconciliation loop pattern — was extracted and simplified into Kubernetes, making Borg arguably the most influential piece of infrastructure software that most engineers have never directly used.