Alex,
We are doing just what you describe, although we do it under the naked
domain.
we have app.io pointing to appengine, which has a wildcard certificate
mapped.
My appengine settings for custom domain are like this:
custom domain name | cert | record type | data | alias
*.app.io |
We are in the middle of the migration. It is a horrible experience.
We tried to break it into small steps.
Still in python2, we first replaced memcache with redis and replaced
search with elasticsearch. These steps were do-able.
Next we tried to make the python2 code compatible with python3
