People love to build new systems from scratch, but the real world is full of large & messy systems with limited documentation, manual processes, huge technical debt, and a myriad of problems. These often need to be taken over, stabilized, managed, optimized & upgraded for the long-term, usually without downtime, a process can take a week, a month, or a year. This is a large-scale Managed Service Provider's look at their last decade of the tools and processes to do this on 1, 10, and 100+ million-user systems on the ever-chaotic Chinese Internet.