Google App Engine Shim? NDB Middleware receiving an error

I have the following sync service written as a microservice.

Per the google cloud instructions I could add the middleware? shown at the bottom as a type of shim? I don't have a good mental model of what this does, could I ask for some help clarifying.

Should I expect that code at the bottom to be available and in memory when the /keepalive/ path is traversed?

app.route('/keepalive/', methods=['GET'])
def keepalive():


  collection_dbs, collection_cursor = model.Collection.get_dbs(
    order='name'
  )
  ...

  return 'ok'

...

import google.appengine.api

client = ndb.Client()
def ndb_wsgi_middleware(wsgi_app):
    def middleware(environ, start_response):
        with client.context():
            return wsgi_app(environ, start_response)

    return middleware

app.wsgi_app = ndb_wsgi_middleware(google.appengine.api.wrap_wsgi_app(app.wsgi_app))

Thanks

1. Since you're using the cloud version of ndb, you need a client - which is why you're doing

   client = ndb.Client()
   

2. The documentation says any use of ndb must be within the context of a call to context() i.e.

   client = ndb.Client()
   with client.context():
       # Use NDB for some stuff
       pass
   

3. I'm not sure what model.collection means in your code but if it's coming from ndb, then you would ordinarily have had to encase it within (wrap it) with client.context() i.e.

   with client.context():
       collection_dbs, collection_cursor = model.Collection.get_dbs(
           order='name'
       )
   

4. Google documentation says that if your webapp uses a WSGI framework, you can prevent having to manually wrap each of your calls to ndb with a with client.context(), by creating a middleware to automatically do this for you. Since it's a middleware, I believe you have to (should) initialize/define it at the top of your code so that it applies to the rest of your code

   from flask import Flask
   from google.cloud import ndb
   
   client = ndb.Client()
   
   
   def ndb_wsgi_middleware(wsgi_app):
       def middleware(environ, start_response):
           with client.context():
               return wsgi_app(environ, start_response)
   
       return middleware
   
   
   app = Flask(__name__)
   app.wsgi_app = ndb_wsgi_middleware(app.wsgi_app)  # Wrap the app in middleware.
   
   
   app.route('/keepalive/', methods=['GET'])
   def keepalive():
     collection_dbs, collection_cursor = model.Collection.get_dbs(
       order='name'
     )
     ...
   
     return 'ok'
   

5. If you want something similar to your Python 2 code (where you didn't have to create clients or worry about context), you can use the bundled services SDK