Graceful upgrades in Go

What this post added

This post introduces the 'tableflip' Go library, designed to implement NGINX-style graceful upgrades for Go applications. It details the challenges of graceful upgrades, including issues with plain `exec()`, `SO_REUSEPORT` race conditions, and the need for a controlled lifecycle. The library allows for inheriting net.Listeners, managing unused sockets, and signaling readiness to the parent process, ensuring that upgrades can occur without service interruption and with minimal risk of dropped connections or failed initializations.