Moving your application from one type of infrastructure to another always involves effort, whether it's from a single hosted server to a set of load-balanced hosts, or from one cloud provider to another.

Unless you expect to migrate between cloud providers relatively often, and/or have built your application to be "cloud native" up-front (implying low cost to move to the cloud), it may be cheaper and swifter simply to perform a one-time rewrite and redeployment once you've chosen a desired deployment platform.