Troubleshooting an ASP.NET Core App Running in Docker

Andrew Lock, the author of the new book ASP.NET Core in Action, has graciously allowed us to repost his recent article about an issue he had with a "missing connection string" error in a new ASP.NET Core application running in Docker. In the article, not only does he cover basic background of environments in ASP.NET Core, he also describes how you would use environment-specific configuration. He describes the bug and provides his solution.