I have a service web running in the url service.old_domain.com (hosted in an internal DNS service)
Now I want to do a redirection from the url service.new_domain.com (hosted in an external DNS service)
Is it enough with adding a CNAME in the external DNS service like:
service.new_domain.com -> service.old_domain.com
Or shall I add a type A like:
service.new_domain.com -> IP address of "service.old_domain.com"
It depends on your future plans and possible scenarios. CNAME is enough, but in future you may decide to completely remove
service.old_domain.com
and that will break yourservice.new_domain.com
until you fix it. In case of A record you will have to change it if your server IP changes. If you have small network and both future scenarios are not likely, create either CNAME or A, both will work.