  Modern soft X-ray observatories can yield unique insights into time domain
astrophysics, and a huge amount of information is stored - and largely
unexploited - in data archives. Like a treasure-hunt, the EXTraS project
harvested the hitherto unexplored temporal domain information buried in the
serendipitous data collected by the European Photon Imaging Camera instrument
onboard the ESA XMM-Newton, in 16 years of observations. All results have been
released to the scientific community, together with new software analysis
tools. This paper presents the architecture of the EXTraS science gateway, that
has the goal to provide the software to the scientific community through a Web
based portal using the EGI Federated Cloud infrastructure. The main focus is on
the light software architecture of the portal and on the technological insights
for an effective use of the EGI ecosystem.
