upgrade

Overview ¶

Package upgrade implements zero-downtime restarts by handing the listening sockets to a freshly-exec'd copy of the binary. The child inherits the bound listener file descriptors and starts accepting on them immediately, so the data-plane ports never close; the parent then drains its existing connections and exits.

Listeners participate by creating their sockets through ListenTCP / ListenUDP instead of binding directly: on a normal start these bind fresh and register the socket for later handoff; after an upgrade they transparently adopt the inherited socket matching their address.

Socket inheritance relies on passing file descriptors to a child process, which is only available on Unix-like systems. On other platforms an upgrade request returns an error and ListenTCP / ListenUDP simply bind fresh.