The Munin master

For an overview see Architectural Fundamentals

Role

The munin master is responsible for gathering data from munin nodes. It stores this data in RRD [1], files, and graphs them on request. It also checks whether the fetched values fell below or go over specific thresholds (warning, critical) and will send alerts if this happens and the administrator configured it to do so.

[1]

RRDtool (acronym for round-robin database tool) aims to handle time-series data like network bandwidth, temperatures, CPU load, etc. The data are stored in a round-robin database (circular buffer), thus the system storage footprint remains constant over time. Source Wikipedia: http://en.wikipedia.org/wiki/RRDtool

Components

The following components are part of munin-master:

munin-cron runs munin-limits and munin-update. munin-update is run by munin-cron. It is the munin data collector, and it fetches data from munin nodes, which is then stored in RRD files.

munin-limits is run by munin-cron. It notifies any configured contacts if a value moves between “ok”, “warn” or “crit”. Munin is commonly used in combination with Nagios, which is then configured as a contact.

Additionally munin 2.0 contains two more components:

munin-graph is run by munin-cron. It generates static graphs in PNG format. It is not needed if munin-httpd is used. munin-cgi-graph is run by a web server, and generates graphs on request.

munin-html is run by munin-cron. It generates static HTML pages. It is not needed if munin-httpd is used. munin-cgi-html is run by a web server, and generates HTML pages on request.

Configuration

The munin master has its primary configuration file at /etc/munin/munin.conf.

Fetching values

• Data exchange between master and node
  • Connect to the node
  • Node commands
  • Example outputs

Graphing Charts

Other documentation

• Let Munin croak alarm
  • Sending alerts through Nagios
  • Alerts send by local system tools
  • Syntax of warning and critical
  • Reformatting the output message
  • Munin Alert Variables
• Scaling the munin master with rrdcached
  • Configuring rrdcached
  • Configuring munin to use rrdcached
  • Is it working?
  • Monitoring rrdcached