  When a network application is implmented as a virtual machine on a cloud and
is used by a large number of users, the location of the virtual machine should
be selected carefully so that the response time experienced by users is
minimized. As the user population moves and/or increases, the virtual machine
may need to be migrated to a new location or replicated on many locations over
a wide-area network. Virtual machine migration and replication have been
studied extensively but in most cases are limited within a subnetwork to be
able to maintain service continuity. In this paper we introduce a distributed
cloud computing environment which facilitates the migration and replication of
a virtual machine over a wide area network. The mechanism is provided by an
overlay network of smart routers, each of which connects a cooperating data
center to the Internet. The proposed approach is analyzed and compared with
related works
