Abstract-Workflow engines [1][2][3] often being based on WS-BPEL, currently rely on a mix of recovery / modification strategies [4] that are either part of the workflow description, part of the workflow engine, or realized as plugins to the workflow engine. To foster the development of distributed cloud-based workflow engines and novel repair algorithms, workflow engines have to be modularized in order to overcome the static and inflexible APIs provided by these workflow engines. Dynamic features gained by a modularization include the creation of external modules to monitor as well as modify a workflow to provide error handling in conjunction with Service Level Agreement (SLA) constraints. The aim of this paper is to present a flexible Workflow Execution Engine to facilitate the development of a new dynamic infrastructure to realize dynamic workflow engines with a focus on cloud-based environments.