One way to host

A Flask web app on Heroku

Planigale..

is a guessing game for matching a photo of a cute critter with their genus and species made by Lin Taylor and myself during the first half of W1.

Progression

• Take cute critter data from an API source
• Create console game using OOP
• Adapt the console game to a web based flask application running locally
• Pretify the layout and styling for the app
• Host the application on heroku

Current Architecture

• Application Code - Python w/ Flask & Jinja2
• Container - Gunicorn
• Storage - Redis
• Host - Heroku

Flask is awesome

• Annotations
• Sessions
• G (a helpful but sometimes confusing global)

Redis is awesome

• Easy to set up key-value store
• Enables server side sessions

Serialization/deserialization..

can be tricky

• Not straightforward with nested class structure (OOP!!)
• Used jsonpickle to make serialization easy
• Deserialization needed careful definition of constructors. Be careful of:
  • Equality tests that rely object references
  • Updates that rely upon object references

Things that work fine locally..

but not on Heroku/Gunicorn

• Random secret key for sessions.

• Global variables for storing application state.

• Pickle for serializing / deserializing objects. Just use JSON.

• Defining global functions in jinja2 template to reference python built-ins.

Other gotchas..

that just don't work

• Cookies are limited to 4 KB in size, so are your flask client side sessions - be mindful about what objects you're storing in session.

• But.. Free tier of Redis to Go is limited to 5 MB. So try to limit the amount of data that you store on the server side as well.

fin.