Upgrading Existing Clusters
If your organization has applications and services that currently run on the Windows NT 4.0 or Microsoft® Windows® 2000 operating systems, you can upgrade your existing WLBS or Network Load Balancing clusters to take advantage of the improved security and performance of Windows Server 2003 and Network Load Balancing. Figure 9.8 shows the process for upgrading an existing cluster.
Figure 9.8 Upgrading an Existing Cluster
The Network Load Balancing upgrade process assumes the following conditions:
Your applications are running on an existing IIS 4.0 (on Windows NT 4.0) or IIS 5.0 (on Windows 2000).
You are upgrading the operating system and services running on your existing application servers.
The system resources of the computers in your existing application farm are sufficient, or can be upgraded, to support Windows Server 2003 and IIS 6.0.
You can upgrade a cluster by taking the entire cluster offline and upgrading all the hosts, or you can leave the cluster on line and perform a rolling upgrade. A rolling upgrade entails taking individual cluster hosts offline one at a time, upgrading each host, and returning the host to the cluster. You continue upgrading individual cluster hosts until the entire cluster is upgraded. A rolling upgrade allows the cluster to continue running during the upgrade.
The decision to use rolling upgrades is based on the applications and services running on your existing cluster. If the applications and services support rolling upgrades, then perform a rolling upgrade on the existing cluster. Otherwise, perform the upgrade process recommended for the applications and services running on the cluster. For more information on the upgrade process for the applications and services running on your cluster, see "Additional Resources for Deploying Network Load Balancing" later in this chapter.
Upgrade the cluster by using the information documented in the "NLB Cluster Host Worksheet" that your design team completed for each cluster host during the design process.