=======
 monit
=======
.. contents::
   :local:

Official docs
=============

https://mmonit.com/monit/documentation/monit.html
  Main docs.
https://mmonit.com/wiki/Monit/ConfigurationExamples
  Real-world configuration examples.
https://mmonit.com/wiki/Monit/FAQ
  FAQ

Debugging monit
===============

Run standalone::

  monit -c /path/to/monitrc

Check syntax::

  monit -t
  monit -t -c /path/to/monitrc

Override log file location in config::

  set log /var/log/monit.log

or with CLI option::

  monit -l /var/log/monit.log

Do not go into background::

  monit -I

Make verbose output::

  monit -v
  monit -vv

Full length commant may look like::

  sudo monit -v status
  sudo monit -Iv validate
  sudo monit -Ivv -c /path/to/monitrc

To debug start/stop scripts write wrapper that redirects STDIO to file::

  #/bin/sh
  exec 1>my.log
  exec 2>my.log
  echo "$@"
  exec "$@"

Limiting server to ``localhost``::

  set httpd port 2812
    use address localhost
    allow localhost
    allow admin:monit

Monit modes
===========

* In ``active`` mode (the default), Monit will pro-actively monitor a service and in case of
  problems raise alerts and/or restart the service.
* In ``passive`` mode, Monit will passively monitor a service and will raise alerts, but will not
  try to fix a problem by executing start, stop or restart.
* In ``manual`` mode, Monit will enter active mode only if a service was started via Monit.

Example::

  check process App with pidfile /var/run/app.pid
    start program = "/usr/bin/app start"
    stop program = "/usr/bin/app stop"
    mode passive

Alerting
========
::

  check process memcached with match memcached
    start program = "/usr/bin/systemctl start memcached"
    stop program = "/usr/bin/systemctl stop memcached"
    if failed host 127.0.0.1 port 11211 protocol MEMCACHE then restart
    if cpu > 70% for 2 cycles then alert
    if cpu > 98% for 5 cycles then restart
    if 2 restarts within 3 cycles then timeout

  check process myapp with pidfile /run/myapp.pid
    if does not exist then alert

  check filesystem Ubuntu with path /dev/sda1
    if space usage > 90% then alert
  check filesystem Home with path /dev/sda3
    if space usage > 90% then alert

  check host app_name with address 127.0.0.1
    start "/sbin/start app_name"
    stop "/sbin/stop app_name"
    if failed port 80 protocol HTTP
      request /ok
      with timeout 5 seconds
      then restart

Running monit by systemd
========================
::

  [Unit]
  Description=Pro-active monitoring utility for unix systems
  After=network.target
  Documentation=man:monit(1) https://mmonit.com/wiki/Monit/HowTo

  [Service]
  Type=simple
  KillMode=process
  ExecStart=/usr/local/bin/monit -I
  ExecStop=/usr/local/bin/monit quit
  ExecReload=/usr/local/bin/monit reload
  Restart = on-abnormal
  StandardOutput=null

  [Install]
  WantedBy=multi-user.target

https://mmonit.com/wiki/Monit/Systemd
  Official docs.

Monitor systemd process
=======================

With pid-file::

  check process nginx with pidfile /var/run/nginx.pid
    start program = "/bin/systemctl start nginx"
    stop program = "/bin/systemctl stop nginx"

If process without pid-file::

  check program MyApp with path "systemctl --quiet is-active MyApp"
    if status != 0 then ...

There is a way to tell systemd to create pid-file if process doesn't to it itself::

  ExecStartPost=/bin/sh -c "echo $MAINPID > /run/myapp.pid"

By matching program name::

  check process MyApp matching 'myapp.*'
     start program = /bin/app
     stop program = something..

Can systemd replace monit?
==========================

No. Systemd has only basic check if process is running. Imaging that process is stuck. You need some
active probes, like HTTP health endpoint.

Systemd has limited capabilities for notifying with ``OnFailure``::

  [Service]
  Restart=always
  RestartSecs=30

  [Unit]
  OnFailure=...

Reverse proxy for monit
=======================

Ngnix::

  server {
    listen   80;
    server_name  my.server.name;
    location /monit/ {
      allow 127.0.0.1;
      allow 192.0.0.0/8;
      deny all;

      proxy_pass http://127.0.0.1:2812;
      proxy_set_header Host $host;
      rewrite ^/monit/(.*) /$1 break;
      proxy_ignore_client_abort on;
    }
  }