I need to deploy my Flask web app (with a database) to the cloud. I don't want to invest considerable amount of time on setup, that's why I want to go with PaaS, not IaaS.

As of 2017, what are the viable options for hosting low traffic web-app (few thousand visits per month) with sudden spikes in traffic (500+ realtime users)?

I am deciding between Heroku and App Engine(both have free tier, which is great), but since I don't know much about it would like to get your advice. Thanks!