—Popular online services such as social networks, e-commerce and bidding are routinely hosted in large-scale data centers. Group communication systems (e.g., multicast) and distributed key-value stores are among some of the most essential building blocks for these services. Due to their scaling requirements, overlay networks such as distributed hash tables (DHTs) have been traditionally used in such systems. Modern hierarchical datacenter networks and global services running across datacenters pose unique challenges that traditional systems are ill-equipped to handle. For instance, the inherent multirooted tree topology design with oversubscription at the core translates into lesser bandwidth at the upper levels of the trees; traditional systems do not take this into consideration leading to a wastage of precious network resources. To solve this problem, we introduce a hierarchy-aware distributed overlay framework called DC2, for large scale and highly dynamic services. We build two ...