Monitoring services & more with monit

Intro

Monit is a tool we can use to monitor any number of things on the Linux installations in AWS — from CPU usage to Internet connectivity.
* Website: https://mmonit.com/monit/
* Lots of configuration help can be found here and google. https://mmonit.com/wiki/Monit/ConfigurationExamples

We’re going to use it to monitor solr. Solr is a search database `systemd` service that occasionally fails without warning, possibly rendering your  application useless. Having at least a notification email sent out will help you  proactively address an issue before users/customers notice it.

Setup
Setup is fairly straightforward.
1. Install monit
`sudo apt-get install monit`
2. Edit (with sudo) the `/etc/monit/monitrc` file. This file contains all the rules and configurations. Copy/paste the file below *(`/etc/monit/monitrc`), completely overwriting the existing one. Make these changes as needed

  • Alert email format
  • desired alert recipient list
  • Desired action on service anomaly. The provided file has solr set up for passive mode, so a solr failure will simply be logged in /var/log/monit.log` and an email will be sent. Change the mode from passive to active, and monit will persistently try to restart the service on its own.
  • Desired services to monitor. You can add add’l service besides solr, just following the example. Nginx, mongod, etc.
  • Desired frequency (in seconds) of status checking

3. Once the `monitrc` file is edited, you must restart monit for changes to take effect. `sudo service monit restart`. If it complains, do `journalctl -xe` to see where the syntax error is, likely it’s due to a typo in the `monitrc` config file.
That’s it! Install monit, copy/paste the config making the needed format changes, and restart monit. You can test the notifications by stopping solr, waiting for the periodic polling to register the downed service, and checking the specified alert email address for an email.
***

*Don’t be intimidated by the lengthy file below. Almost all of it is commented out, just helpful example for when you want to config stuff.

### `/etc/monit/monitrc` config file
“`
###############################################################################
## Monit control file
###############################################################################
##
## Comments begin with a ‘#’ and extend through the end of the line. Keywords
## are case insensitive. All path’s MUST BE FULLY QUALIFIED, starting with ‘/’.
##
## Below you will find examples of some frequently used statements. For
## information about the control file and a complete list of statements and
## options, please have a look in the Monit manual.
##
##
###############################################################################
## Global section
###############################################################################
##
## Start Monit in the background (run as a daemon):
#
set daemon 300 # check services at 2-minute intervals
# with start delay 240 # optional: delay the first check by 4-minutes (by
# # default Monit check immediately after Monit start)
#
#
## Set syslog logging. If you want to log to a standalone log file instead,
## specify the full path to the log file
#
set logfile /var/log/monit.log
#
#
## Set the location of the Monit lock file which stores the process id of the
## running Monit instance. By default this file is stored in $HOME/.monit.pid
#
# set pidfile /var/run/monit.pid
#
## Set the location of the Monit id file which stores the unique id for the
## Monit instance. The id is generated and stored on first Monit start. By
## default the file is placed in $HOME/.monit.id.
#
# set idfile /var/.monit.id
set idfile /var/lib/monit/id
#
## Set the location of the Monit state file which saves monitoring states
## on each cycle. By default the file is placed in $HOME/.monit.state. If
## the state file is stored on a persistent filesystem, Monit will recover
## the monitoring state across reboots. If it is on temporary filesystem, the
## state will be lost on reboot which may be convenient in some situations.
#
set statefile /var/lib/monit/state
#
#

## Set limits for various tests. The following example shows the default values:
##
# set limits {
# programOutput: 512 B, # check program’s output truncate limit
# sendExpectBuffer: 256 B, # limit for send/expect protocol test
# fileContentBuffer: 512 B, # limit for file content test
# httpContentBuffer: 1 MB, # limit for HTTP content test
# networkTimeout: 5 seconds # timeout for network I/O
# }

## Set global SSL options (just most common options showed, see manual for
## full list).
#
# set ssl {
# verify : enable, # verify SSL certificates (disabled by default but STRONGLY RECOMMENDED)
# selfsigned : allow # allow self signed SSL certificates (reject by default)
# }
#
#
## Set the list of mail servers for alert delivery. Multiple servers may be
## specified using a comma separator. If the first mail server fails, Monit
# will use the second mail server in the list and so on. By default Monit uses
# port 25 – it is possible to override this with the PORT option.
#
# set mailserver mail.bar.baz, # primary mailserver
# backup.bar.baz port 10025, # backup mailserver on port 10025
# localhost # fallback relay
#
#
set mailserver smtp.gmail.com port 465
username USERNAM password “PASSWORD”
using ssl
## By default Monit will drop alert events if no mail servers are available.
## If you want to keep the alerts for later delivery retry, you can use the
## EVENTQUEUE statement. The base directory where undelivered alerts will be
## stored is specified by the BASEDIR option. You can limit the queue size
## by using the SLOTS option (if omitted, the queue is limited by space
## available in the back end filesystem).
#
set eventqueue
basedir /var/lib/monit/events # set the base directory where events will be stored
slots 100 # optionally limit the queue size
#
#
## Send status and events to M/Monit (for more informations about M/Monit
## see http://mmonit.com/). By default Monit registers credentials with
## M/Monit so M/Monit can smoothly communicate back to Monit and you don’t
## have to register Monit credentials manually in M/Monit. It is possible to
## disable credential registration using the commented out option below.
## Though, if safety is a concern we recommend instead using https when
## communicating with M/Monit and send credentials encrypted.
#
# set mmonit http://monit:monit@192.168.1.10:8080/collector
# # and register without credentials # Don’t register credentials
#
#
## Monit by default uses the following format for alerts if the the mail-format
## statement is missing::
# –8<–
set mail-format {
from: monit@$HOST
subject: monit alert — $EVENT $SERVICE (TEST solr)
message: $EVENT Service $SERVICE
Date: $DATE
Action: $ACTION
Host: $HOST
Description: $DESCRIPTION

You are likely receiving this email because solr is down in TEST. You may want to investigate.

for any questions, contact the dev team,
xyz@ourSite.com
}
#–8 4 then alert
# if loadavg (5min) > 2 then alert
# if cpu usage > 95% for 10 cycles then alert
# if memory usage > 75% then alert
# if swap usage > 25% then alert
#
#
## Check if a file exists, checksum, permissions, uid and gid. In addition
## to alert recipients in the global section, customized alert can be sent to
## additional recipients by specifying a local alert handler. The service may
## be grouped using the GROUP option. More than one group can be specified by
## repeating the ‘group name’ statement.
#
# check file apache_bin with path /usr/local/apache/bin/httpd
# if failed checksum and
# expect the sum 8f7f419955cefa0b33a2ba316cba3659 then unmonitor
# if failed permission 755 then unmonitor
# if failed uid root then unmonitor
# if failed gid root then unmonitor
# alert security@foo.bar on {
# checksum, permission, uid, gid, unmonitor
# } with the mail-format { subject: Alarm! }
# group server
#
#
## Check that a process is running, in this case Apache, and that it respond
## to HTTP and HTTPS requests. Check its resource usage such as cpu and memory,
## and number of children. If the process is not running, Monit will restart
## it by default. In case the service is restarted very often and the
## problem remains, it is possible to disable monitoring using the TIMEOUT
## statement. This service depends on another service (apache_bin) which
## is defined above.
#

check process solr
matching “solr”
mode passive
alert devel@temis.us

# check process apache with pidfile /usr/local/apache/logs/httpd.pid
# start program = “/etc/init.d/httpd start” with timeout 60 seconds
# stop program = “/etc/init.d/httpd stop”
# if cpu > 60% for 2 cycles then alert
# if cpu > 80% for 5 cycles then restart
# if totalmem > 200.0 MB for 5 cycles then restart
# if children > 250 then restart
# if loadavg(5min) greater than 10 for 8 cycles then stop
# if failed host http://www.tildeslash.com port 80 protocol http
# and request “/somefile.html”
# then restart
# if failed port 443 protocol https with timeout 15 seconds then restart
# if 3 restarts within 5 cycles then unmonitor
# depends on apache_bin
# group server

#
#
## Check filesystem permissions, uid, gid, space and inode usage. Other services,
## such as databases, may depend on this resource and an automatically graceful
## stop may be cascaded to them before the filesystem will become full and data
## lost.
#
# check filesystem datafs with path /dev/sdb1
# start program = “/bin/mount /data”
# stop program = “/bin/umount /data”
# if failed permission 660 then unmonitor
# if failed uid root then unmonitor
# if failed gid disk then unmonitor
# if space usage > 80% for 5 times within 15 cycles then alert
# if space usage > 99% then stop
# if inode usage > 30000 then alert
# if inode usage > 99% then stop
# group server
#
#
## Check a file’s timestamp. In this example, we test if a file is older
## than 15 minutes and assume something is wrong if its not updated. Also,
## if the file size exceed a given limit, execute a script
#
# check file database with path /data/mydatabase.db
# if failed permission 700 then alert
# if failed uid data then alert
# if failed gid data then alert
# if timestamp > 15 minutes then alert
# if size > 100 MB then exec “/my/cleanup/script” as uid dba and gid dba
#
#
## Check directory permission, uid and gid. An event is triggered if the
## directory does not belong to the user with uid 0 and gid 0. In addition,
## the permissions have to match the octal description of 755 (see chmod(1)).
#
# check directory bin with path /bin
# if failed permission 755 then unmonitor
# if failed uid 0 then unmonitor
# if failed gid 0 then unmonitor
#
#
## Check a remote host availability by issuing a ping test and check the
## content of a response from a web server. Up to three pings are sent and
## connection to a port and an application level network check is performed.
#
# check host myserver with address 192.168.1.1
# if failed ping then alert
# if failed port 3306 protocol mysql with timeout 15 seconds then alert
# if failed port 80 protocol http
# and request /some/path with content = “a string”
# then alert
#
#
## Check a network link status (up/down), link capacity changes, saturation
## and bandwidth usage.
#
# check network public with interface eth0
# if failed link then alert
# if changed link then alert
# if saturation > 90% then alert
# if download > 10 MB/s then alert
# if total upload > 1 GB in last hour then alert
#
#
## Check custom program status output.
#
# check program myscript with path /usr/local/bin/myscript.sh
# if status != 0 then alert
#
#
###############################################################################
## Includes
###############################################################################
##
## It is possible to include additional configuration parts from other files or
## directories.
#
include /etc/monit/conf.d/*
include /etc/monit/conf-enabled/*
#

“`