Building a Multi-tenant Cloud Service from Legacy Code with Docker Containers

In this paper we address the problem of migrating a legacy Web application to a cloud service. We develop a reusable architectural pattern to do so and validate it with a case study of the Beta release of the IBM Bluemix Workflow Service [1] (herein referred to as the Beta Workflow service). It uses Docker [2] containers and a Cloudant [3] persistence layer to deliver a multi-tenant cloud service by re-using a legacy codebase. We are not aware of any literature that addresses this problem by using containers.The Beta Workflow service provides a scalable, stateful, highly available engine to compose services with REST APIs. The composition is modeled as a graph but authored in a Javascript-based domain specific language that specifies a set of activities and control flow links among these activities. The primitive activities in the language can be used to respond to HTTP REST requests, invoke services with REST APIs, and execute Javascript code to, among other uses, extract and construct the data inputs and outputs to external services, and make calls to these services.Examples of workflows that have been built using the service include distributing surveys and coupons to customers of a retail store [1], the management of sales requests between a salesperson and their regional managers, managing the staged deployment of different versions of an application, and the coordinated transfer of jobs among case workers.