Choosing between Google Cloud Flexible or Standard Environment

I'm starting to build a web/mobile app that is going to be offered as SaaS. I have seen many cloud options for hosting (Heroku, AWS) but finally decided to go with Google Cloud App Engine.

My back-end will be Java based, and I'm confused about going with the Standard or Flexible Env. I have read several docs online but still undecided.

Considerations to tackle:

1. I am not very experienced with Docker and this is my first Saas App.

2. My app should run perfectly with the offering of the Standard Env.

3. Migrating from the Standard to the Flex environment seems to bring some headache.

Would you please help me decide on the way to?

We try to cover the key differences in this doc:

https://cloud.google.com/appengine/docs/the-appengine-environments

To cover your considerations:

1. You don't need to understand Docker to use flex or standard
2. If your app can run in Standard - that's great!
3. Migrating from Standard to Flex is a fair bit of work. We try to cover it here

Read over those docs, and let me know if you have any other questions!