How to force DNS refresh for a website?

As far as I know, a forced update like this is not directly possible. You might be able to reduce the DNS downtime by reducing the TTL (Time-To-Live) value of the entries before changing them, if your name server service provider allows that.

Here's a guide for less painful DNS changes.

A fair warning, though - not all name servers between your client and the authoritative (origin) name server will enforce your TTL, they might have their own caching time.

There's no guaranteed way to force the user to clear the DNS cache, and it is often done by their ISP on top of their OS. It shouldn't take more than 24 hours for the updated DNS to propagate. Your best option is to make the transition seamless to the user by using something like mod_proxy with Apache to create a reverse proxy to your new server. That would cause all queries to the old server to still return the proper results and after a few days you would be free to remove the reverse proxy.

you can't force refresh but you can forward all old ip requests to new one. for a website:

replace [OLD_IP] with old server's ip

replace [NEW_IP] with new server's ip

run & win.

echo "1" > /proc/sys/net/ipv4/ip_forward

iptables -t nat -A PREROUTING -d [OLD_IP] -p tcp --dport 80 -j DNAT --to-destination [NEW_IP]:80

iptables -t nat -A PREROUTING -d [OLD_IP] -p tcp --dport 443 -j DNAT --to-destination [NEW_IP]:443

iptables -t nat -A POSTROUTING -j MASQUERADE