Many distributed applications require 24/7/365 availability, and still need to be updated. We analyze how to update such applications on-the-.y. This a challenging task not only because performing the updates without closing the application is dif.cult, but also because updates may introduce potential version con.icts between various application components. We develop a framework (called DUCS) that facilitates dynamic updates of component-based distributed applications. DUCS supports adaptation of existing applications, dynamic component replacement, state transfer, and interface modi.cations by utilizing so-called interface adapters.