A quick overview of how Devmon works
- Devmon starts by reading the list of hosts to monitor from its database.
- In a single-node setup, the database is stored in
hosts.db. In a multi-node setup, it's stored in a MySQL database. - The database must be populated at least once using the
--readbbhostsflag before Devmon can monitor anything.
- Devmon reads its templates.
- In a single-node setup, templates are read from disk at the start of each polling cycle.
- In a multi-node setup, templates are read from the database, but only if they've been updated since the last read.
- Devmon performs SNMP queries on all devices in its database.
- Queries are optimized to avoid redundant queries for the same SNMP OID across multiple tests for a device.
- Devmon applies template logic to the SNMP data received.
- This involves transformations, applying thresholds, and generating a message for the display server.
- The message includes a timestamp, the overall device status (red, yellow, green), and an HTML page with detailed device information.
- Devmon sends the rendered messages to the display server.
- Devmon sleeps for the remaining time in the polling cycle.
This structured approach outlines the sequential steps Devmon takes to monitor devices and communicate status updates to the display server.