DESY is operating amongst others two of the largest accelerator based light sources of the world, the 2.3 km circumference high brilliant synchrotron light source PETRA III and the 3.4 km long European free electron laser XFEL. PETRA III circles the DESY Campus while the XFEL facility runs from the DESY campus in Hamburg to the town of Schenefeld in Schleswig-Holstein. An upgrade to PETRA IV to a diffraction limited light source is planned for 2025 to 2027. The requirements on beam diagnostic and instrumentation of these machines are touching extremes in many aspects. This talk compares and discusses the active or planned instrumentation which fulfil the needs and ensure stable operations of the accelerators.