Server platforms Toolkit

Cluster Service with IIS: How and why

Tags:
Application Level,
Failover,
Network Load Balancing,
NLB

Carol Bailey MCSE+I Tech Republic

Published: 23 Oct 2002 08:54 BST

The standard advice on offering high availability with IIS is to use network load balancing (NLB) rather than the Cluster Service. You can't use both of these clustering techniques on the same servers. NLB works at the network level by distributing client requests to a number of clustered servers (up to 32 in a single cluster). Should a single server fail, this will be detected by the other servers, and new connections will be automatically distributed among the remaining servers.

NLB is a good option for many Web servers running IIS, and because more than two servers can be used with Windows 2000 Advanced Server, it provides for true scaling. However, there may be occasions when you want to use Cluster Service with IIS instead, such as when you want fault tolerance between only two servers and are already using Cluster Service for other resources.

It's also important to remember that NLB works only at the network level, so if, for example, the IIS service stopped or crashed but the server itself remained up, NLB would still direct users to the failed service because it would be unable to verify resources at the application level.

Issues with the Cluster Service and IIS
When using the Cluster Service with IIS, you must take the following issues into consideration:

Using the IIS Server Instance resource, you can cluster the WWW service or FTP service, but you must be running the WWW service even if you want to cluster only FTP. SMTP and NNTP have their own cluster resources (SMTP Server Instance and NNTP Server Instance).
Microsoft FrontPage Server Extensions are not supported on clustered Web sites.
Failed ASP or FTP sessions will not successfully fail over to the other server. The client will have to restart these on the second server. So it's worth remembering that in most cases, a failover will require the user to reestablish the connection.
If your Web site uses the MS DTC (for transaction processing), you must run Comclust.exe on each server to install the MS DTC resource, and you should configure this to depend on the IP address that will be used for your IIS virtual server.
You should make sure that IIS is not configured for the default of All Unassigned IP Addresses but for specific addresses. Your clustered IIS site should be configured to use the virtual server address you will assign with the Cluster Service.
If using anonymous authentication with IIS, you should change the anonymous user account from a local account to a domain account, which will be accessible to both servers (for the same reason that NTFS permissions with File Share resources should not use local accounts).
If you want to use host headers with a clustered Web site, you must set the ServerAutoStart property for that site. For more information, see "Contents of Internet Information Server 5.0 Release Notes" [Q250979] and search for ServerAutoStart.
The IIS resource has only one dependency: the IP Address. However, if your clients will be accessing the site by name, it would be a good idea to add the Name Resource and configure it to have a dependency on the IP Address.
You can use the IISSync utility to synchronise IIS configuration between the two servers. See "Using IISSYNC to Synchronise Clustered Web Sites on Windows 2000" [Q249603] for instructions. Or simply manually set up the two servers with the same configuration.