Tools and strategies to monitor the ATLAS online computing farm

In the ATLAS experiment the collection, processing, selection and conveyance of event data from the detector front-end electronics to mass storage is performed by the ATLAS online farm consisting of nearly 3000 PCs with various characteristics. To assure the correct and optimal working conditions the whole online system must be constantly monitored. The monitoring system should be able to check up to 100000 health parameters and provide alerts on a selected subset. In this paper we present the assessment of a new monitoring and alerting system based on Icinga. This is an open source monitoring system derived from Nagios, granting backward compatibility with already known configurations, plugins and add-ons, while providing new features. We also report on the evaluation of different data gathering systems and visualization interfaces.