A dynamic cluster is a server cluster that uses weights
and workload management to balance the workloads of its cluster members
dynamically, based on performance information that is collected from
the cluster members. Dynamic clusters enable application server virtualization.
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 Intelligent Management autonomic
functions, including high availability and service policies.
For complete life-cycle management servers, the product controls
the creation and deletion of server instances and can start and stop
servers. For assisted life-cycle management servers, the product can
control the state of servers by stopping and starting servers from
a pool of predefined server instances.
Dynamic cluster membership
Two options exist
for adding members to a dynamic cluster: automatically define cluster
members with rules or manually define cluster members.
- Automatically define cluster members with rules
By automatically
defining cluster members with rules, you can create a subexpression
that automatically selects nodes to host dynamic cluster members based
on different node properties. This subexpression is called a membership
policy. After you create the membership policy, you can preview
the node membership before you finish creating the dynamic cluster.
Automatically
defining cluster members with rules is available only for servers
that have complete life-cycle management. After you create the dynamic
cluster with a membership policy, dynamic cluster instances can start
on any of the selected nodes. If nodes become available that meet
the criteria of your membership policy, dynamic cluster instances
can also start on these nodes.
- Manually define cluster members
When you manually define cluster
members, you statically define which servers are cluster members by
selecting servers to add to the cluster. You use this option instead
of the membership policy for the following reasons:
- You have an existing static cluster that you want to convert to
a dynamic cluster.
- You are using assisted life-cycle management servers.
Assisted life-cycle management servers cannot be created from the
administrative console. With this option, you create representations
of the servers as cluster members. These members must be homogeneous,
that is, be all of the same server type, for example, a group of BEA
WebLogic servers. The same version of the middleware software must
be installed on all the nodes in the dynamic cluster, and you must
deploy the same applications to these servers before you create the
dynamic cluster.
Server templates
A server template is
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 middleware server types. You can also define your
own server templates.
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: When you make a change to a dynamic cluster server
template, this will overwrite any changes you made that are unique
to an individual member of that cluster.
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.
- Specifying if cluster instances from other dynamic clusters can
start on the same node, also known as dynamic cluster isolation.
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.
If you are using manual mode
for the autonomic request flow manager (ARFM) on either the cell level
or deployment target level, then you also must put your dynamic clusters
in manual mode. You can also use static clusters when ARFM is in manual
mode for the cell or deployment target. If ARFM is in automatic mode,
you can use any of the operating modes for the cluster.