On every GCP server I have running right now, the default user is the beginning of your email address linked to the Google cloud account. For example my Google Cloud account is linked to sys.bkm@gmail.com and any server I set up there is going to have a default user account of “sys_bkm” (the underscore is an automatic replacement thing Google does because they don’t like periods).
So when I set up a production server I use the following command on GCP
sudo python install.py --production --user sys_bkm
As for not having sudo available to you, that wouldn’t make much sense because you needed it in order to run the install script like above.
No, because on Google Cloud Platform you already have a default user. All you have to do is include it in the --user swith when you run the install.py script.
As @clarkej accurately points out, I do in fact add the user when I am on a paid production server like Interserver, Hostwinds, or DigitalOcean where I have root access. However on the Google Cloud Platform as you indicated you were using, the user account is generated for you and given sudo access because Google does NOT allow root logins. All you have to do is use the default user account that Google assigned to your server in your --user switch.
Hope this helps to clarify the use of the switch and why it is important on Google Cloud PLatform.
BKM