Cloud computing needs to provide integrity assurance in order to support security sensitive application services such as critical dataflow processing. In this paper, we present a novel RObust Service Integrity Attestation (ROSIA) framework that can efficiently verify the integrity of stateful dataflow processing services and pinpoint malicious service providers within a large-scale cloud system. ROSIA achieves robustness by supporting stateful dataflow services such as windowed stream operators, and performing integrated consistency check to detect colluding attacks. We have implemented ROSIA on top of the IBM System S dataflow processing system and tested it on the NCSU virtual computing lab. Our experimental results show that our scheme is feasible and efficient for large-scale cloud systems. Categories and Subject Descriptors: H.4 [Information Systems Applications]: General General Terms: Security, Management, Verification