Our company hosts about 400 websites, divided over multiple shared hosting environments on 4 virtual servers. All the virtual servers are getting a new IP address, so we need to update the DNS settings for every domain and we need to change the settings on the servers. We use Plesk on all servers (different version though, 3 on Windows and 1 on Linux).
How can we handle this IP update smoothly? Simply updating the DNS records and the IP of the domain on the server will cause downtime because the DNS update is delayed. What are standard procedures for this?