A dynamic cluster is a server cluster that uses weights
to balance the workloads of its cluster members dynamically, based
on performance information that is collected from the cluster members.
A dynamic cluster is an application deployment target that
can expand and contract depending on the workload in your environment.
Dynamic clusters work with autonomic managers, including the application
placement controller and the dynamic workload manager to maximize
the use of your computing resources. Dynamic clusters are required
for many of the WebSphere® Extended Deployment autonomic
functions, including high availability and service policies.
Dynamic clusters are similar to the server clusters that you can
create with WebSphere Application Server Network Deployment, but
key differences exist that make dynamic clusters much more robust.
Dynamic cluster membership
In all WebSphere Extended
Deployment Version
6.0 releases, dynamic clusters are tightly coupled with node groups.
Node groups are collections of WebSphere Application Server nodes that define
a boundary for server cluster formation. When you create a dynamic
cluster, you select a node group from which to base your dynamic cluster.
Depending on the settings that you select for your dynamic cluster,
cluster instances are created on the nodes in the node group. Each
node group can contain one or more dynamic clusters. The computing
power of the node group is divided autonomically among the dynamic
clusters, according to the defined business goals.
Server templates
Server templates are
a copy of a server configuration that can be used as a starting point
when a server is added to the dynamic cluster. Predefined templates
exist for different versions of WebSphere Extended Deployment.
Dynamic cluster server templates
After you
create a dynamic cluster, the
dynamic cluster server template defines
the properties for all of the members in the dynamic cluster.
Avoid trouble: Any changes that you make to dynamic cluster server
templates overwrite all changes that you make directly
to dynamic cluster members.
gotcha
Cluster instances
You can control the creation
and management of cluster instances for your dynamic cluster. These
options include:
- Creating a minimum and maximum number of cluster instances.
- Stopping cluster instances when other dynamic clusters need resources.
- Allowing more than one cluster instance to start on the same node,
also known as vertical stacking. With vertical stacking, you
can improve bottleneck conditions within an application. The stacking
number defines how many cluster instances can start on a single
node.
Operating modes
Dynamic clusters act differently
depending on the operating mode. Choose one of the following options
for mode of operation:
- Manual. In manual mode, the dynamic cluster is no different
from the standard application server environments with static clusters.
Manual mode does not support application placement, or runtime task
suggestions. The autonomic request flow manager and dynamic workload
management (DWLM) can work with the cluster.
- Supervised. In supervised mode, the environment provides
information about required corrective actions by generating runtime
tasks. You can accept or deny the recommendations of the autonomic
managers in the task management panel in the administrative console.
To manage runtime tasks, click .
- Automatic. In automatic mode, the environment takes corrective
actions automatically.
Important: To use dynamic application placement,
click automatic or supervised as
the mode of operation.