Script for restarting Django on-the-fly -- creates new instance on another port, switches nginx to it, kills old instance.

fix_nginx_port_on_startup.sh

#!/bin/sh

#   Should be called on system startup from /etc/rc.local
#   for restoring default backend ports previously switched by restart_django.sh

fix_nginx_port() {
        local nginx_config="/etc/nginx/sites-available/$1.conf"
        test -w "$nginx_config" || { logger "ERROR: $nginx_config not writable."; return 1; }
        local main_port="$2" backup_port="$3"
        grep -q -- ":$backup_port;" $nginx_config || return
        sed -i -e "s,:$backup_port;,:$main_port;," $nginx_config
        nginx -s reload
}

# Usage sample..
fix_nginx_port  site1   8100 8101
fix_nginx_port  site2   8200 8201

restart_django.sh

#!/bin/sh

test $# = 3 || { echo "Usage: ${0##*/} /path/to/nginx.conf port1 port2"; exit 1; }

nginx_config="$1"
port1="$2"
port2="$3"

Die() { echo "Error: $*"; exit 1; }

test -w "$nginx_config" || Die "$nginx_config is not writable."

listens_on() { pgrep -f "/manage.py runfcgi host=127.0.0.1 port=$1 pidfile=/" > /dev/null; }

fix_nginx() {
        local old_port="$1" new_port="$2"
        sed -i "s,:$old_port;,:$new_port;," $nginx_config
        grep -q ":$new_port;" $nginx_config ||
                Die "cannot set port $new_port in $nginx_config"
        nginx -s reload
}

swap_ports() {
        local old_port="$1"
        local new_port="$2"

        local old_pid=`pgrep -f "/manage.py runfcgi host=127.0.0.1 port=$old_port pidfile=/"`
        local new_pid=`pgrep -f "/manage.py runfcgi host=127.0.0.1 port=$new_port pidfile=/"`
        test -n "$old_pid" || Die "nothing listens on $old_port?"
        test -n "$new_pid" && Die "already listens on $new_port?"

        local    user="$(ps ho  user $old_pid)"
        local old_cmd="$(ps hwwo cmd $old_pid)"
        local new_cmd="$(echo $old_cmd | sed -e s,port=$old_port,port=$new_port,)"
        local pid_file="$(echo $old_cmd | sed -e 's,.* pidfile=,,' -e 's, .*,,')"

#       echo DEBUG: pid_file = $pid_file
#       echo DEBUG: old_port = $old_port, old_cmd = $old_cmd
#       echo DEBUG: new_port = $new_port, new_cmd = $new_cmd
#       return

        sudo -H -b -n -u "$user" -- $new_cmd # >/dev/null 2>&1
        sleep 1
        new_pid=`pgrep -f "/manage.py runfcgi host=127.0.0.1 port=$new_port pidfile=/"`
        test -n "$new_pid" || Die "nothing listens on new $new_port?"
        echo $new_pid > "$pid_file"

        fix_nginx $old_port $new_port
        sleep 1
        kill "$old_pid"
}

if test "${0#*restart}" = "$0"; then
        fix_nginx "$port2" "$port1"
elif listens_on "$port1"; then
        swap_ports "$port1" "$port2"
elif listens_on "$port2"; then
        swap_ports "$port2" "$port1"
else
        Die "Nothing listens on $port1 nor $port2?"
fi

## END ##