World-wide online monitoring interface of the ATLAS experiment

The ATLAS collaboration accounts for more than 3000 members located all over the world. The efficiency of the experiment can be improved allowing system experts not present on site to follow the ATLAS operations in real-time, spotting potential problems which otherwise may remain unattended for a non-negligible time. Taking into account the wide geographical spread of the ATLAS collaboration, the solution of this problem is to have all monitoring information with minimal access latency available world-wide. We have implemented a framework which defines a standard approach for retrieving arbitrary monitoring information from the ATLAS private network via HTTP. An information request is made by specifying one of the predefined URLs with some optional parameters refining data which has to be shipped back in XML format. The framework takes care of receiving, parsing and forwarding such requests to the appropriate plugins. The plugins retrieve the requested data and convert it to XML (or optionally to JSON) format before giving it back to the framework, which forwards it to the original requester. The list of data types which can be retrieved is fairly complete and includes raw physics event samples, operational statistics, application logs, configuration parameters, data quality assessment results and histograms for the current data taking session as well as for the previous ones. In addition to the traditional request-response information access, the latest version of the framework offers asynchronous data access where it initiates data transmission towards clients only when requested data has changed, reducing the network load and simplifying the development of end-user interfaces. This paper presents the architecture of the ATLAS world-wide framework and summarizes the experience of its usage during the first ATLAS data taking period. It also describes new recently developed plugins as part of the preparation of the second round of the experiment operations planned to start in early 2015.