Chris Matchett

:: node.js - keep alive with bash script and cron ::

For whatever reason I cannot get monit to keep node alive on a ubuntu lucid virtual machine. I've no problem getting monit to carry out the same task on CentOS virtual machines.

So I wrote a little bash script to keep node alive and run it every minute with cron.

#!/bin/bash
PIDFILE=/home/node/app/pids/node.pid 
NODE=/home/node/local/node/bin/node 
APP=/home/node/app/app.js 

echo 'Checking if node is active' 

if [ -f $PIDFILE ] ; then
  if [ -d "/proc/`cat $PIDFILE`" ]; then
      echo "Script is running"
  else
      echo "Script is not running - attempting to Start"
      rm -f $PIDFILE
      $NODE $APP & echo $! > $PIDFILE&
  fi else

  echo "Script is not running - attempting to Start"
  rm -f $PIDFILE
  $NODE $APP & echo $! > $PIDFILE& 
fi 

(The script was inspired by Stephen, http://stephen.rees-carter.net/2011/05/simple-bash-keep-alive-script/)

A little gotcha I encountered was that node couldn't load modules and bombed out as a result. I guess cron reads in your bashrc and as I had put path stuff for node in .profile modules couldn't be located. The following changes to the crontab file fixed these problems. 

SHELL=/bin/bash 
PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/home/node/local/node/bin 
NODE_PATH=/home/node/local/node:/home/node/local/node/lib/node_modules 
HOME=/home/node

# m h dom mon dow command
*/1 * * * * /home/node/scripts/keep-node-alive.sh

All is working well now. The final stage would be to turn off cron messages so you don't end up with a million messages telling you "Script is running".