A fibre-optic, EM-insensitive measurement for the deformation of in-vessel components has successfully been installed and operated at the nuclear fusion experiment ASDEX Upgrade. The sensors were tested for their neutron tolerance and vacuum compatibility. Installation was done by copper-steel laser beam welding. Measurements of in-service oscillations due to all three existing types of load cases show good agreement with theory and simulations. A fatigue lifetime assessment was performed.