Deploying keras Model to Production on Google Cloud

Deploying a model to production is an important skill that a Machine Learning Engineer should add to his skillset. I trained a MNIST model and created a writing interface. User can draw a digit using the interface and the model would predict the digit.
App Running

I made an app.yaml file and tried deploying it on Google Cloud using Google Cloud SDK. After successful deployment, there was a server error when using the command gcloud app browse(maybe due to error in the app.yaml)
Server Error