HI we have deployed a internet site to our users and we have plan to patch SQL Server by installing service pack 3 and we have downtime.
For end users how to show a maintenance page to users when they browse sharepoint web application from internet
Thanks to Ref link
Maintenance Page for SharePoint - Quick way to Implement
Here is the quick way to implement Maintenance page in SharePoint, during scheduled down times/upgrade/service pack patching: Create a new app_offline.htm file in IIS Root folder of your SharePoint site. Place some descriptive text/images to the file, Make sure the file size is at least 512 bytes (otherwise, you will get 404 page not found error!). That's all!
I've placed the maintenance page content like this:
<html xmlns="http://www.w3.org/1999/xhtml"> <head> <meta http-equiv="Content-Type" content="text/html; charset=utf-8" /> <title>Site Under Maintenance</title> </head> <body> <div align="center"><br /> <br /> <br /> <br /> <img src="http://testIntranet.crescent.com/images/maintenance.gif" width="600" height="300" /></div> </body> </html>
and the output: Maintenance page for SharePoint 2010/2013
As long as this file exists in the root, ASP.NET shuts down the site, stops processing any requests. So, After the maintenance activity, Just delete the app_offline.htm file to end up the maintenance mode.
For some reasons, If this doesn't work for you: Create a dummy website in TEST environment, assign the PROD site's Host headers, Place the above content in Index.htm, change the IP addresses in publishing server! (ISA/ F5).