Add support for user-data and meta-data via HTTP

[mschmitt]

Thanks for your script which got us kickstarted on Ubuntu autoinstalls quite nicely. Coming from debian-installer it was a bit of a shock, but I've come to appreciate the leanness of the user-data file.

Since after the initial lab work on autoinstalling, work has shifted to modifications on the user-data file, I thought it might be a good idea to let the ISO remain static and let it retrieve the configuration by HTTP. We're currently installing in two ways: PXE install with vmlinuz/initrd/iso/meta-/user-data over the network, and customized ISO image. Using this patch, both methods can use the same meta-data/user-data files from an http server.

[covertsh]

Hi, thanks so much for your contribution. What are your thoughts on using the -u argument and detecting whether it is a URL, rather than introducing a new argument and the logic to handle a conflict between them?

[mschmitt]

The issue with auto-detecting an URL in -u is that -u stands for --user-data but the URL is a base path where both files will be located. After detection of -u as a URL, an additional -m will still have to be handled, so auto-detection in -u will be a trade-off between:

• One less option -b and improved clarity without the "alternative to -u and -m" clause and
• -u suddenly being used to specify the location of both user-data and meta-data.

I see today that I ruined README.md by copying the output from --help with expanded variables from my system, so the PR isn't ready to merge as it is anyway. Let me know what you prefer and I'll implement it accordingly.

[mschmitt]

Still here (back from vacation), and updated --user-data with URL detection, as suggested. :-)

[covertsh]

Hope you enjoyed your vacation. Thanks for making another commit - apologies for not responding sooner, I was also taking time off. To be honest I don't have any problem with the original implementation; it makes sense when you explain it. Which do you prefer?

[mschmitt]

Let's go with the converged -u. I'm already focusing on the upcoming 22.04, which is a whole new bag of surprises. ;-)