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#!/bin/bash

# nginx-upgrade - Upgrade all running nginx instances with zero downtime

# Upgrade all running nginx instances by sending the USR2 signal to the
# master process of each instance, then gracefully stopping the old master.
# This allows for zero-downtime upgrades of nginx.

# Last updated: 2026-03-08

TIMEOUT=10

wait_for_file() {
	# usage: wait_for_file <present|absent> <file> <label>
	local mode=$1 file=$2 label=$3
	local i

	for ((i=0; i<TIMEOUT; i++)); do
		[[ $mode == present && -f $file ]] && return 0
		[[ $mode == absent  && ! -f $file ]] && return 0
		sleep 1
	done

	echo "ERROR: $label - file never ${mode}ed: $file" >&2
	return 1
}

upgrade_instance() {
	# usage: upgrade_instance <service-unit> <pid-file>
	local unit="$1" pid_file="$2"
	local old_pid_file="${pid_file}.oldbin"

	if [ ! -f "$pid_file" ]; then
		echo "[$unit] No PID file at $pid_file - skipping."
		return 0
	fi

	echo "[$unit] Starting new master process..."
	/bin/systemctl kill --signal=SIGUSR2 --kill-who=main "$unit"

	wait_for_file present "$old_pid_file" "$unit - new master start" || return 1

	echo "[$unit] New master is up. Gracefully stopping old master..."
	local old_pid
	old_pid=$(cat "$old_pid_file" 2>/dev/null)
	/bin/kill -s QUIT "$old_pid" 2>/dev/null

	wait_for_file absent "$old_pid_file" "$unit - old master stop" || return 1

	echo "[$unit] Done."
	return 0
}

overall_rc=0

# Discover every active nginx instance via systemctl
instances=$(systemctl list-units --type=service --state=running --no-legend "nginx*" |
	awk '{print $1}' |
	grep -E '^nginx(@\w+)?\.service$')

for unit in $instances; do
	pid_file=$(systemctl show "$unit" -p PIDFile --value)

	if [ -z "$pid_file" ]; then
		echo "[$unit] Could not determine PID file - skipping." >&2
		continue
	fi

	upgrade_instance "$unit" "$pid_file"
	rc=$?
	[ $rc -ne 0 ] && overall_rc=$rc
done

exit $overall_rc

: <<'POD'
=pod

=head1 NAME

nginx-upgrade - tool to upgrade nginx without any downtime

=head1 SYNOPSIS

nginx-upgrade

=head1 DESCRIPTION

This downstream shell script updates nginx without any downtime. After
upgrading nginx via the package manager, running this script will create
a new nginx master. This master takes over all new requests. The old
masters and workers are then gracefully shutdown without breaking any
existing connections.

For further information, see: L<http://nginx.org/en/docs/control.html>

=head1 BUGS

If you find any bugs, please send an email to the author.

=head1 AUTHORS

Felix Kaechele E<lt>felix@kaechele.caE<gt>

Originally written by
Jamie Nguyen E<lt>jamielinux@fedoraproject.orgE<gt>

=cut
POD