sorry for another question : Is it common to automate setting a custom domain (xxx.com from godaddy) to azure web app using pulumi as well? or do it manually once and pulumi up command would not delete binding since then? Thank you!

Yes, it's common to manage as much as possible through Pulumi. As a general rule, you don't want to manually make changes to a resource that's under Pulumi's management. In your case, the domain name should probably be a configuration value. This will also allow you to deploy several stacks with different domains for testing.

awesome! like a github, if i sync every state of cloud as possible it has huge benfit(for managing). I got a concept of Iac, thank you! it's bit a pain to figuring out each custom property like a custom domain though.

Exactly. It's a bit of a learning curve in the beginning, but I have yet to find anyone who wants to go back to managing infrastructure in any other way.