Intelligent client computing devices track and record the changes they make to data, applications, and services. Systems, devices, and computer readable media for detecting service tier failures and maintaining application services provide a resilient client architecture that allows a client application on an intelligent client to automatically detect the unavailability of server tiers or sites and re-route requests and updates to secondary sites to maintain application services at the client tier in a manner that is transparent to a user. The resilient client architecture understands the level of currentness of secondary sites in order to select the best secondary site and to automatically and transparently bring this secondary site up to date to ensure no data updates are missing from the secondary site.