Plan for multiple clusters
Multiple clusters are sets of servers managed together within a single administrative domain (or cell), and participate in workload management. IBM WebSphere Application Server Network Deployment can manage many application servers and application server clusters within a single administrative domain, or cell. The single cell has the following advantages:
- A single administration user interface (WebSphere Integrated Solutions Console)
- A single administrative scripting client (wsadmin)
- Shared resources at the cell, node, or server scope
- Replication domains for sharing application data, state information, and caches
- Workload management at the web server level provides a single-server identity for all applications hosted across the cell.
HCL WebSphere Portal can federate multiple, independently configured portal and non-portal clusters into the same cell. For example, one cluster provides portal, and the other can provider Web 2.0 services such as Ajax and REST. might
How multiple clusters work in a single cell
A cell's scope controls the visibility of a resource to other resources and application server instances. An example of a resource might be a data source definition, a certificate, or WebSphere variable definition. Scopes include:
| Cell | All resources defined are visible to all other resources defined in the cell. Therefore, they are globally available. |
| Node | A cell has one or more nodes. Each node is associated matches with a WAS profile on some physical server. Resources defined at this scope are visible only to other resources defined in this same node, including any server definitions. |
| Server | A node has one or more server definitions. Resources defined at this scope are visible only to that server. No other server or node can use these resources. |
| Cluster | A resource defined at a cluster scope is visible to all cluster members, or server instances, in this cluster. However, it is not visible to any other servers in the same nodes. |
Note that all enterprise applications are cell-scoped. In other words, there can be only one enterprise application with a given name in the cell. If multiple servers and clusters, or multiple clusters require the use of that enterprise application, they must share it. To install an enterprise application across multiple clusters, the administrator installs the EAR file into the cell's Deployment Manager, and then maps the application to the target clusters where it runs. HCL WebSphere Portal installs several enterprise applications as part of its basic configuration and before any cluster is defined. Special steps must be followed to ensure that these infrastructure applications are appropriately shared when multiple clusters are defined within the same cell. And by extension, since they are infrastructure applications, all HCL WebSphere Portal clusters must be at the same version. It is possible, but not always appropriate, to share portlets across multiple clusters. Many portlets (for example HCL WebSphere Portal administration) are considered part of the infrastructure, and as a result can be shared across multiple clusters. Most user application portlets are specific to certain clusters and are installed as such.
The JEE security configuration for the cell is shared by all servers and clusters managed in the cell. Therefore, each server and cluster must share an underlying user repository:
- A common security model, including user repositories, for every cluster
- Some number of common enterprise applications and portlets that must be made common as part of the federation and clustering process
- Install portlets into certain clusters, or across clusters, as appropriate
- Understand how to tell if enterprise applications are shared between clusters
- Define other resources at the appropriate scope, depending on the usage goals
Limitations
All portal clusters must be at the same maintenance levels. HCL WebSphere Portal is made up of several enterprise applications. These applications are tightly coupled to the underlying services and infrastructure. All portal-based clusters in the same cell must be at the same service level.
When multiple clusters need access to a common Process Server, centralize the server within its own cluster. Use HCL WebSphere Portal with the client installation of the Process Server to allow remote access to the central process server cluster.
See also