11.4 node/pool select according to domains list

Customer can add more domains in future, since its dynamic hosting environment, Is it possible to load external datagroup list file which can be updated periodically? Or is there any API in F5 that can be used as upload url where I can upload the update datagroup ?

There are several ways to manage data groups. You can use an internal data group (that gets stored in the config), or an external, file-based, data group. In both cases you can use iControls remotely and shell scripts (bash, perl, python, etc.) locally to manage the content of the data groups. It really depends on how you want to do it.

Does the dg file should look like that: "www.domain1.com" := "www.domain1.com" "www.domain2.com" := "www.domain2.com" "www.domain3.com" := "www.domain3.com"

You don't need a value in the data group - just the string. Example:

www.domain1.com :=
www.domain2.com :=
www.domain3.com :=
www.domain4.com :=
...