In TCP, what happens if I use strange hosts?

I am registering a host according to the form. My question is as follows:

  1. What happens if I register a non-existent host such as 'aaaaabbbbbccc.com'?

  2. How long is the timeout while connecting to an unresponsive host?

  3. I wonder if it performs synchronously or asynchronously for a large number of hosts.

Hi! Heartbeat will return an error for non existent DNS entries. The default timeout is 16s. Heartbeat is async.