How do I obtain proper App Engine module hostname

Question

According to the docs on App Engine, when using the appspot.com domain you have to do some trickery with -dot- instead of . in subdomains.

Please note that in April of 2013, Google stopped issuing SSL certificates for double-wildcard domains hosted at appspot.com (i.e. ..appspot.com). If you rely on such URLs for HTTPS access to your application, please change any application logic to use "-dot-" instead of ".". For example, to access version "1" of application "myapp" use "https://1-dot-myapp.appspot.com" instead of "https://1.myapp.appspot.com." If you continue to use "https://1.myapp.appspot.com" the certificate will not match, which will result in an error for any User-Agent that expects the URL and certificate to match exactly.

I am trying to figure out the best way to generate these URLs using the SDK without manually replacing the dots. I've tried modules.get_hostname(module="my module name") but it returns a traditional sub-domain that triggers the SSL mismatch error.

Edit Per suggestion, I opened a feature request for this functionality

Answer 1

So given for example

x = 'https://1.amodule.myapp.appspot.com'

you need to replace all but the last two dots with -dot- (the last two must remain since the .appspot.com part much stay untouched).

Given this, I'd recommend:

>>> x = 'https://1.amodule.myapp.appspot.com'
>>> dots = x.count('.')
>>> x.replace('.', '-dot-', dots - 2)
'https://1-dot-amodule-dot-myapp.appspot.com'

The key ideas: x.count('.') tells you how many dots in all string x contains; the third optional argument to x.replace tells Python how many dots, at most, are to be replaced.

Answer 2

The gcloud command-line utility now has gcloud app browse, which will take you to the correct URL. For example, the following commands will launch the URL https://1-dot-amodule-dot-myapp.appspot.com:

gcloud config set project myapp
gcloud app browse --service="amodule" --version="1"

Or

gcloud app browse --project="myapp" --service="amodule" --version="1"

By default it will attempt opening the URL in a browser, but you can use the --no-launch-browser flag to only display the URL.

Full docs at https://cloud.google.com/sdk/gcloud/reference/app/browse.