I was working on a Web App which uses a SQL database and EntityFramework. The app is hosted in Azure. I spent some time fixing up the csproj file so that the build and release pipelines work correctly i.e. once the code is committed to the repository, a build is kicked off and deployment takes place.

So far so good. However on visiting the site I see this error:

Error : The underlying provider failed on Open. Stack Trace : at System.Data.Entity.Core.EntityClient.EntityConnection.Open() at System.Data.Entity.Core.Objects.ObjectContext.EnsureConnection(Boolean shouldMonitorTransactions)

Hmmm. The code runs perfectly locally, where is this error coming from? I updated the web.config and eventually added the connection strings to Azure App Service > Configuration Connection string in Azure App Service

No luck.

Then I found the Azure App Service > Diagnose and solve problems > Diagnostic Tools > Profiler Diagnose and solve problems

Then selected the “Check Connection String”, et voila the error is seen in a web.config under the Views. That saved the day for me. There are a few other tools on that page which I will investigate down the track. For now this was a good find !