I am currently writing my first dotnet core 2.0 application deployed to a Linux environment. The development has been on a Mac using a combination of the dotnet cli and Visual Studio for Mac.

In deploying the app to a QA site, we experienced an error I’ve never seen before

An exception occured reading app key DeviceId default value  applied.
System.IO.IOException: The configured user limit (128) on the number of inotify instances has been reached.
   at System.IO.FileSystemWatcher.StartRaisingEvents()
   at System.IO.FileSystemWatcher.StartRaisingEventsIfNotDisposed()
   at Microsoft.Extensions.FileProviders.Physical.PhysicalFilesWatcher.CreateFileChangeToken(String filter)
   at Microsoft.Extensions.Primitives.ChangeToken.OnChange(Func`1 changeTokenProducer, Action changeTokenConsumer)
   at Microsoft.Extensions.Configuration.Json.JsonConfigurationSource.Build(IConfigurationBuilder builder)
   at Microsoft.Extensions.Configuration.ConfigurationBuilder.Build()
   at app.Shared.Utilities.GetAppConfig[T](String key, T defaultValue) in /var/app/source/app/app.Shared/Utilities.cs:line 33
   at System.IO.FileSystemWatcher.StartRaisingEvents()
   at System.IO.FileSystemWatcher.StartRaisingEventsIfNotDisposed()
   at Microsoft.Extensions.FileProviders.Physical.PhysicalFilesWatcher.CreateFileChangeToken(String filter)
   at Microsoft.Extensions.Primitives.ChangeToken.OnChange(Func`1 changeTokenProducer, Action changeTokenConsumer)
   at Microsoft.Extensions.Configuration.Json.JsonConfigurationSource.Build(IConfigurationBuilder builder)
   at Microsoft.Extensions.Configuration.ConfigurationBuilder.Build()

I didn’t know where to start so I Googled the issue and landed on some StackOverflow questions and GitHub issues associated with the same issue. The most helpful questions and answers came from the following sources.

• https://www.danieldevelops.com/inotify-watcher-dotnet-core
• https://stackoverflow.com/questions/45875981/error-while-reading-json-file-in-dotnet-core-the-configured-user-limit-128-on
• https://github.com/dotnet/corefx/issues/5660
• https://github.com/dotnet/corefx/issues/21934

My solution was to replace the call to WebHost.CreateDefaultBuilder(..) with a modified version of Microsoft’s implementation but with the following changes:

• Make appsettings.json a required file (this was for my needs, you can change is to not be required)
• Remove adding appsettings.{env}.json as we don’t use it. I am considering add this back to the gist.
• Disable reloading the configuration when appsettings.json is modified (this is what instantiates FileSystemWatcher and causes our error)
• Remove IIS integration (as we are deploying the app on Linux-based docker containers)

The modified method is available as a GitHub gist.