Highly compartmentalized network segmentation is a long-held goal of most blue teams, but it's notoriously hard to deploy once a system has already been built. We leveraged an existing service discovery framework to deploy a large-scale TLS-based segmentation model that enforces access control while automatically learning authorization rules and staying out of the way of developers. We also did it without scheduling downtime or putting a halt to development. This talk covers how we engineered this, and shares lessons learned throughout the process.