Admonitor was created out of my need for a simple and lightweight monitoring system that could be easily extended.

It's not webscale, but is aimed at those situations where you have a few dozen servers that you need to monitor and don't want to install something like Icinga or Nagios.

It's written in Perl, so if this is a language that you are familiar with, then it is very easy to write additional monitoring plugins.

The design is very modular. It consists of one central server, with agents running on individual servers.

Each host being monitored has a small daemon installed to monitor the required resources (e.g. memory, CPU). The daemon logs the required characteristics to a local SQLite database. This means that if there are any communication problems, then the logging will still take place. Periodically, the central server will contact each host and download its statistics.

The central server performs a number of functions:

Retrieving statistics from host

Periodically the central server will contact each host to retrieve the statistics that are being monitored internally by the agent (e.g. memory, CPU).

Performs external monitoring

It performs monitoring of those services that can be checked externally. E.g. pings, HTTP requests.

Alerts

If pre-defined criteria are met, then the central server sends alerts. At the moment, only email alerts are possible.

Analytics

The central server contains a web service, which can be used to view graphs of metrics over time. This is useful (for example) to see exactly when a spike in memory use occurred, which can help in tracking down the cause.

Modules come in 2 flavours:

Agents (Plugin::Agent::)

These sit on the hosts being monitored and record data locally, which is then transferred to the central server. The modules themselves contain some code that is run on the agent, and some that is run on the server. For example, the read method is run on the host being monitored; the write and alarm methods are run on the server.

Checkers (Plugin::Checker::)

These monitor something external, and only run on the controller.

Quick and dirty installation instructions for Debian.

# Install required modules
apt-get install -y libsys-statistics-linux-perl libdbd-sqlite3-perl libmoo-perl \
  libdatetime-format-strptime-perl libmoox-types-mooselike-perl libconfig-any-perl \
  libjson-perl liblog-report-perl libyaml-perl libmail-box-perl libcpanel-json-xs-perl

# Install Admonitor modules
cp -a lib/Admonitor /usr/local/share/perl/a.b.c/

# Install agent script
cp bin/admonitor-agent.pl /usr/local/bin/

# Install service
cp etc/admonitor.service /etc/systemd/system/
systemctl enable admonitor.service

# Add required users
groupadd --system admonitor
useradd --system -g admonitor admonitor

# Install config
mkdir /etc/admonitor
cp etc/agent.yaml /etc/admonitor/
chmod 640 /etc/admonitor/agent.yaml
chown admonitor /etc/admonitor/agent.yaml

# Update agent.yaml as required

# Start the daemon
systemctl start admonitor

The controller is a Dancer2 application, although the plan is to remove the dependency on Dancer2 in the future.

Install the whole repo to a web server location (e.g. /srv) and then:

Create a blank database in MySQL or PostgreSQL

Install the schema using DBIx::Class::Migration

DBIC_MIGRATION_USERNAME=xxx DBIC_MIGRATION_PASSWORD=xxx dbic-migration -Ilib \
  --schema_class='Admonitor::Schema' --dsn='dbi:mysql:database=admonitor' \
  --dbic_connect_attrs quote_names=1 install

Copy config.yml-example to config.yml and update as required. Choose the Admonitor plugins that you wish to enable, and add the database configuration to the DBIC plugin section.

Manually connect to the database and then:

Add a row to the user table, adding just firstname, surname, email, username

Add a row to the host table for each host to be monitored

Only name and password should be added. The password for each host should match the corresponding password in the configuration file on the host.

Add rows to the host_checker table

If a checker is not set to all_hosts in the config file, then a row has to be added to stipulate which hosts should be monitored with which checkers. This is only for external checkers, not the agents that run on each host.

The intention is for this to become a constantly-running service in the future, but at the moment it is a cron job that runs periodically.

Create an admonitor user, and add a cron job for the get-agent-data script. For example, to collect the data every 15 minutes:

5,20,35,55 * * * * /srv/admonitor/bin/get-agent-data.pl

This will contact each host, collect the statistics, and save to the database on the controller.

There are aspects of the application's design that I would like to change. If you start using Admonitor, please let me know, so that I can keep you informed of any changes.