High-performance proxies like Envoy support 'Hot Restart'. What is the low-level mechanism that allows this process to update its binary/config without dropping active TCP connections?

1. A The Gateway uses an FPGA chip that can reconfigure its internal circuits on the fly while traffic is flowing.
2. B Shared Socket Inheritance: The new process starts and communicates with the old process over a Unix Domain Socket to 'Pass' the file descriptors for the listening ports, then carefully drains active connections.
3. C The Gateway relies on the user's browser to automatically detect the restart and hold the request in a local buffer.
4. D It uses a special 'Quantum Entanglement' feature of modern Linux kernels to sync memory across two processes.