When I setup Google App Engine a few years ago, it doesn't support naked domain directly where it would redirect naked domain to www. As I tested on 2017-12-12, the previous statement is no longer accurate.
Once Google App Engine custom domains is setup, it can be accessed via 3 domains:
mydomain.com(naked domain)www.mydomain.com(www)projectid.appspot.com(appspot domain)
If you want to redirect both naked naked and appspot domain to www, you have to do it via application code.
The following is an example using flask.
from flask import Flask, request, redirectapp = Flask(__name__)@app.before_requestdef handle_before_request(): # prevent cronjob redirect error if 'AppEngine-Google' not in request.user_agent.string: if request.host in ['mydomain.appspot.com', 'mydomain.com']: url = request.url.replace(request.host, 'www.mydomain.com') return redirect(url, code=301)