aws-sdk error in expressjs project - Cannot find module 'aws-sdk/lib/config_service_placeholders
I had the same problem and the solution was embarrassingly simple. I use Visual Studio Code and had accidentally imported a bad, unused file.
Going over your files mentioned in the error output and see if you have imported the wrong file :)
Hope you find it!
If no code changed, the problem is probably corrupted node modules. First step would be removing your node_modules and reinstalling them.
There could also be with a problem with the import statement in your userController.js line 7.