  When orchestrating Web service workflows, the geographical placement of the
orchestration engine(s) can greatly affect workflow performance. Data may have
to be transferred across long geographical distances, which in turn increases
execution time and degrades the overall performance of a workflow. In this
paper, we present a framework that, given a DAG-based workflow specification,
computes the op- timal Amazon EC2 cloud regions to deploy the orchestration
engines and execute a workflow. The framework incorporates a constraint model
that solves the workflow deployment problem, which is generated using an
automated constraint modelling system. The feasibility of the framework is
evaluated by executing different sample workflows representative of sci-
entific workloads. The experimental results indicate that the framework reduces
the workflow execution time and provides a speed up of 1.3x-2.5x over
centralised approaches.
