Re: Anyway to detect application startup failure within monit?

[Lukasz Piwowarek]

Kun,

I use Monit to check Nginx, Node.js and RedisDB and Monit already reports if the service failed to start. I do not know much about Monit - in all cases however my init scripts for these programs are more "standard" if you will - I do not use Monit to start the service - I assume Monit reads the exit code from the init script and reports failure or success based on that.

For example this is how I start RedisDB:

# Variable Definitions

REDIS=/usr/bin/redis-server
CONFIG=/etc/redis.conf
LOCKFILE=/var/lock/subsys/redis

[ -f /etc/sysconfig/redis ] && . /etc/sysconfig/redis

start() {
        if [ -x $REDIS ] ; then
                if [ -f $CONFIG ] ; then
                        echo -n $"Starting RedisDB: "
                        daemon $REDIS $CONFIG
                        RETVAL=$?
                        echo
                        [ $RETVAL -eq 0 ] && touch $LOCKFILE
                        return $RETVAL
                else
                        echo -n $"Cannot find RedisDB configuration at $CONFIG."
                fi
                else -n $"Cannot find RedisDB executable at $REDIS."
        fi
}

Hope this helps.

Cheers

Lukasz

On Tue, Jan 17, 2012 at 5:28 PM, Kun Xi <address@hidden> wrote:

Hello,

tl;dr: go to the end for the question, please.

We are trying to use monit to start/monitor some services, and the
basic workflow is:

Start monit very early as a system-level service using init script.
In service foo init script, create a foo.conf in /etc/monit/conf.d
Reload monit
monit start foo

==== monitrc  snippet ====
set daemon 5
set logfile syslog facility log_daemon
set pidfile /tmp/monit-wfe1.pid
set idfile /var/run/monit/monit.id
set statefile /var/run/monit/monit.state
set httpd port 2812 and use the address 127.0.0.1
   allow localhost

include /etc/monit/conf.d/*
==== monitrc snippet ====

The service foo's monit config
==== conf.d/foo.conf ===

check process foo with pidfile /tmp/foo.pid
  start "/opt/bin/foo --pidfile /tmp/foo-wfe1.pid --instance-id foo-wfe1  -d"
  stop "/sbin/start-stop-daemon --stop --quiet -R 120 --oknodo
--pidfile /tmp/foo-wfe1.pid"
  if failed host 192.168.0.16 port 8086 protocol http
      and request '/ping'
      with timeout 5 seconds for 4 cycles
  then restart
==== conf.d/foo.conf ====

Here is the init script snippet to start service foo:
==== init.d/foo ====
function start() {
  monit_config # create the conf.d/foo.conf using the magic
environment variable
   /usr/sbin/monit -c $MONIT_RC reload
   while :
   do
       sleep 1
       /usr/sbin/monit -c $MONIT_RC start foo
       STATUS=`/usr/sbin/monit -c $MONIT_RC summary | sed -n
"s/Process 'foo' *\([a-z]*\)/\1/p"`
       if [ "$STATUS" = 'running' ]; then
           break
       fi
   done
   RETVAL=0
}
==== init.d/foo ====

The service foo may crash in startup due to the corrupted configure
file, incompatible environment . This approach will keep retrying it,
and to make things worse, monit does not handle the process crash very
well, the stderr is filled with:

monit: cannot read status from the monit daemon

QUESTION:
Any way to detect the process died in the startup in monit, and what
is appropriate approach for monitor to bail out in such a scenario,
for example, unmonitor and return the error status from foo?

Thanks,
Kun

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