Snarl is a monitoring tool for dynamic web applications.
Snarl dynamically creates and assembles URL's and scans them at arbitrary intervals, performs predefined checks on URL content, size and timing, notifies a monitoring application via traps if a predefined error condition (event) has been met and delivers a snapshot of it's current tests and result at any given time.
Snarl is build as a truly multi-threaded MIB module for net-snmp 5.0.3 and higher. its current monitoring status can be retrieved via the net-snmp daemon's snmp request interface.
Configuration of the URL tests is done via a configuration file in a human readable format. all configurations can be hot updated. No data will be lost on reconfiguring a running Snarl.
Snarl is very humble. it can run on an average PC with average sized resources and still is able to monitor up to eight hundred web pages or even more.
Though the only limit should be machine capabilities, the amount of concurrent threads in Snarl has been limited to one thousand parallel monitoring tasks.
The lifetime of a thread is as long as one transaction, usually only a few concurrent threads exist in a typical monitoring environment. a mechanism inside Snarl keeps the amount of concurrent network connections as low as possible by desynchronizing network downloads. This is to account for limits imposed on most machines.
Snarl performs each monitoring test by downloading the content of the monitored URL and thereby causes a http server log file entry on the web server.
Consider this when you monitor web sites that pursue a business model where number of hits is important to the payor or customer.