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 monit

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.. 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;

    }

  }