In the arena of cloud technology, the run and manage of enterprise is driven by optimized computing without compromising the business continuity. The resource cost is optimized to operate as pay per use. So, it becomes imperative to take the legacy applications onto a cloud platform to minimize the TCO and add new features to existing software. To make the cost optimization in cloud platform, the business applications must run in distributed manner in a cloud platform according to best pattern & practice. It is the imperative that we identify all bits and pieces of a business problem in the source legacy environments before we plan a migration move. Here we would discuss the method and process to discover the unknowns as the challenge itself remains the difficult to identify the legacy system component in existing architecture because of dearth of documentation or lack of architecture knowledge on ground who operates these applications.