Even After hosting migration, some user's browsers / system or their ISP provider may not updated new server details such as new ip & dns settings, Now what will happen to that user, can he access site from old server?
If yes is it possible to redirect that user to new server?
For the duration that traffic still goes to the old ip-address 3 common approaches depending on your level of access are possible
configure network address translation on the old ip-address to the new ip-address. This can be done at the level of a router meaning that the old server can be switched off rather than be reconfigured. That will also work on all other protocols and not only http/https
configure the old server to act as a reverse proxy. That will use the old server to perfectly present the content of your new server. The exact configuration depends on your web server but both Nginx and Apache support ProxyPass directives and IIS supports similar functionality with URL rewrite rules. Or you can replace the existing web server with something purposely designed such as HAProxy.
Make your new site available under both the existing domain and a (temporary) new domain and configure the old web server to send http 307 temporary redirect to that new domain, which does resolve correctly to your new op-address.
This question lacks a lot of details...
If the old server still works, users with outdated DNS records can still access it under the old IP address.
Under some circumstances, it will be possible to redirect users to the new server, but this has limitations. As an example, you need to either redirect to the new IP address or a new temporary name and your site needs to be able to deal with this.
