Zeroupgrade upgrades network servers with zero downtime. Unlike nginx and Unicorn, where the upgrading logic is integrated in the program itself, zeroupgrade is a separate binary which does the hard work. Client programs only require minimal changes to allow zero downtime upgrades.
While zeroupgrade is written in Go, client programs may be written in any language.
Zeroupgrade has similarities with Stripe’s Einhorn. If you run systemd, you don’t need zeroupgrade, use systemd’s socket activation.
zeroupgrade -listen localhost:8080 command...
-listen addr may be specified multiple times.
Sending SIGUSR2 to zeroupgrade performs a zero downtime upgrade.
Sending SIGTERM or SIGINT shuts down zeroupgrade and its
child processes.
The only thing client programs must do in order to support zero
downtime upgrades is to listen on specific file descriptors. The
file descriptors (one for each listen address) are given in the
ZEROUPGRADE_FDn environment variables; the file descriptor for
the first listen address being in ZEROUPGRADE_FD0, the second in
ZEROUPGRADE_FD1, and so on.
In Go, it looks like this:
if listenfd := os.Getenv("ZEROUPGRADE_FD0"); listenfd != "" {
n, err := strconv.ParseUint(listenfd, 10, 64)
if err != nil {
panic(err)
}
fd := uintptr(n)
listener, err = net.FileListener(os.NewFile(fd, ""))
if err != nil {
panic(err)
}
}
http.Serve(listener, nil)- Write pidfile