User manual

The WebMux Pro and Model WM108E User Guide – Version 5. 8 Rev15

Appendix 4 – Virtual Hosting Issues

Servers serving more than one web site may do virtual hosting. WebMux

supports virtual hosting by checking the virtual server’s response. There are

three different situations for WebMux to handle.

If the service is HTTPS, there is no way to do virtual hosting on the same IP

addresse. However, each HTTPS farm can be on a different IP address on the

same server. The reason that each HTTPS server must have its own IP address

is that any web server software, IIS or Apache, can not see the URL in the

HTTPS packets, since they are encrypted. The IIS or Apache server only

decrypts the URL after the packet is sent to a particular process. Since no web

server software supports virtual hosting HTTPS on the same IP address,

WebMux does not need to do anything extra other than load balancing all the

packets for that particular farm.

If the service is HTTP, then any web server software, IIS or Apache, can host

almost unlimited virtual farms on each IP address. Many hosting centers handle

this situation by putting all the servers serving each virtual host on a server farm

on the WebMux. The WebMux will load balance the traffic for all the incoming

traffic for that IP address to different servers in that farm. During farm setup, the

label for the farm could be one of the virtual farm’s base URL, say

www.mydomain.com , WebMux actually periodically read a page from this URL.

If server that serves that URL does not response correctly, WebMux will mark

that server dead. Since every server in that farm serves all the virtual farms,

WebMux expects the problem with one server in one URL will affect all the URLs

in that farm.

Another situation is the server that serves HTTP virtual sites using a single

private IP address already before load balancing. After adding load balancer,

some the sites want to have their own IP addresses. WebMux allows set up

separate farm for each site having its own public IP address, but point to the

same sets of servers in the private network. In this situation, each separate farm

could have its own label as www.site1.com and www.site2.com, etc. WebMux

will actually do health check on each URL by periodically read a default page

from that site.

In the virtual hosting situation, the label and response from the web servers are

critical for reliable services. WebMux checks the label and checks the server for

its health situation based on the URL supplied in the label. If the server response

is 500 or greater, which is an error code indicating server internal error, WebMux

will excludes that server from serving the farm. If server responses 402, which

indicating access is denied for that virtual farm, WebMux will mark that server

dead. We have checked with IIS server and Apache server, they both follow the

same rules.