Comment 7 for bug 2004131

> What's the general procedure

Currently cloud-init doesn't have a general method for user-configured networks across different datasources. LXD (also NoCloud) is somewhat unique in that the user has control of the "cloud", which allows the user to set settings that are typically provided by clouds. Since clouds have different networking environments which might not be static, network configuration is typically acquired by cloud-init from the cloud's IMDS.

Manually configuring the network shouldn't be required to get a network-accessible instance on clouds with cloud-init.

If you would like to configure a custom DNS configuration after boot you might try using the runcmd and/or write_files modules.