Envoy supports “runtime” configuration (also known as “feature flags” and “decider”). Configuration settings can be altered that will affect operation without needing to restart Envoy or change the primary configuration. The currently supported implementation uses a tree of file system files. Envoy watches for a symbolic link swap in a configured directory and reloads the tree when that happens. This type of system is very commonly deployed in large distributed systems. Other implementations would not be difficult to implement. Supported runtime configuration settings are documented in the relevant sections of the operations guide. Envoy will operate correctly with default runtime values and a “null” provider so it is not required that such a system exists to run Envoy.