An Algebra for Robust Workflow Transformations

Scientific workflows are often designed with a particular compute site in mind. As a user changes sites the workflow needs to adjust. These changes include moving from a cluster to a cloud, updating an operating system, or investigating failures on a new cluster. As a workflow is moved, its tasks do not fundamentally change, but the steps to configure, execute, and evaluate tasks differ. When handling these changes it may be necessary to use a script to analyze execution failure or run a container to use the correct operating system. To improve workflow portability and robustness, it is necessary to have a rigorous method that allows transformations on a workflow. These transformations do not change the tasks, only the way tasks are invoked. Using technologies such as containers, resource managers, and scripts to transform workflows allow for portability, but combining these technologies can lead to complications with execution and error handling. We define an algebra to reason about task transformations at the workflow level and express it in a declarative form using JSON. We implemented this algebra in the Makeflow workflow system and demonstrate how transformations can be used for resource monitoring, failure analysis, and software deployment across three sites.