I have two web server ( server A & server B ) , running Linux , apache , they are located in two different data center , that means they are hosted by different provider

server A 's IP is 111.111.111.111 , two website are running on it , the url to access these Two website are
http://serverA.com/website1
http://serverA.com/website2


server B 's IP is 222.222.222.222 , one website are running on it , he url to access this website is
http://serverB.com/website3

As these two servers are hosted by two different data center , that means they have different DNS

Now we want relocate ( move / migrate ) server B 's website to server A , but want the url to access these three website are unchanged , as below
http://serverA.com/website1
http://serverA.com/website2
http://serverB.com/website3

Just would like to ask after relocate server B 's website to server A , what conf file need to be change ? how to change the DNS record to make the above three url are unchanged ?

Thanks a lot

If you have a registered domain, your domain registrar should take care of this.

In server A , the hosts file as below

#vi /etc/hosts
111.111.111.111 serverA


What I need to do is add the below entry to the DNS server of the domain registrar ?

#vi /etc/hosts
111.111.111.111 serverB

You don't make it clear if these are publicly available servers with registered domain names or if they are internal servers only.

If they are public available with a registered domain name then you need to find out where the A records for the domain are hosted.

It could be that the domain registrar is providing DNS services, in which case you will need to locate the appropriate A record within the domain and change it. As you look like you're serving with the bare domain then the A record may have a designation of @

If the registrar has delegated DNS services back to you (you'd be able to tell by the NS records for the domain) then you'll need to work out where and how DNS is actually being served and adjust the zone files accordingly.