When you create a dynamic cluster, weights are used to
dynamically balance the workloads of the cluster members, based on
performance information that is collected from the cluster members.
Before you begin
Complete the following prerequisites before creating a dynamic
cluster:
- Create a node group. See Creating or editing a node group
for more
information.
- You must have configurator administrative privileges to create
a dynamic cluster.
- Verify that the application placement controller is enabled. The
application placement controller is enabled by default. The application
placement controller enables the autonomic capabilities of dynamic
clusters. To enable the application placement controller, click .
For more information about the properties that you can change on the
application placement controller, see Monitoring and tuning the application placement controller
- Decide if you are going to use vertical stacking. Vertical
stacking can improve bottleneck conditions in deployed applications
by enabling the placement controller to start more than one instance
of the dynamic cluster on a node. With vertical stacking enabled,
the autonomic managers limit the processor percentage that is used
by each stacked instance. The general formula is 100%/max-number-of-stacked-instances.
For example, if you configure three stacked instances, the workload
is throttled to prevent any single instance form using more than 33%
of the processor capacity. See Configuring vertical stacking
for
more information.
About this task
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 product autonomic functions, including
high availability and service policies.
When you create a dynamic
cluster of application servers, the recommendation is to have a maximum
number of 50 application servers, node agents, and on demand routers
per core group. A dynamic cluster cannot span multiple core groups.
Consider this limit when you set the number of instances and stacking
number for your dynamic cluster. This limitation does not apply to
dynamic clusters of assisted life-cycle servers or complete life-cycle
dynamic clusters of PHP or servers.
Procedure
- Create the dynamic cluster. In the administrative
console, click .
- Enter dynamic cluster information.
In this step you give a name to the dynamic cluster, specify
the node group to which the dynamic cluster is mapped, and define
other dynamic cluster properties.
- Select a dynamic cluster template. You can either
build servers that are based on a default template, or you can use
an existing server from your environment as the template. The displayed templates are valid for the platform
that corresponds to the node group that you selected for your dynamic
cluster. The template also corresponds to the version of your deployment
manager.
- Specify dynamic cluster-specific properties.
- Define the minimum number of cluster instances. The
default minimum number of instances is one instance and the maximum
default is no limit on instances.
- Define the maximum number of cluster instances. The
default value has no limit on the number of cluster instances.
- Determine whether to enable vertical stacking. When
you configure vertical stacking, more than one dynamic cluster instance
can start on the same node.
- Confirm the dynamic cluster creation. Click Finish > Save to
save the changes to the master configuration.
- Select the mode of operation. In the administrative console,
click . Select the dynamic clusters that
you want to modify. Choose the operational mode and click Set
mode.
Important: To use dynamic application
placement, click Automatic or Supervised as
the mode of operation.
If
you have nodes that run on z/OS® systems, use dynamic clusters
in supervised or automatic mode. If you want to prevent WebSphere® Extended Deployment from automatically starting
a cluster member on a logical partition (LPAR) that is hosting a dynamic
cluster when the LPAR processor is too busy, then you must define
the cpuUtilizationThreshold custom property. In this scenario, the
product starts the cluster member only if transaction demand requires
additional cluster members and the processor utilization on the LPAR
is less than the cpuUtilizationThreshold value. See cpuUtilizationThreshold for more information.
Results
The application placement controller
starts a cluster instance on each node for the dynamic cluster. Cluster
instances starts one server on each node concurrently across all of
the nodes in the node group for your cluster. When all of the instances
for the dynamic cluster are started, the cluster instances for another
dynamic cluster in your environment can begin to start.
When the dynamic clusters start, at least one instance
of each dynamic cluster in your environment becomes available as soon
as possible. Multiple instances on the same node can start concurrently
if you have multiple processors on the same node. For example, if
you have two processors on a node, two instances can start concurrently.
The application placement controller continues to start instances
evenly across the nodes for all the dynamic clusters until the minimum
number of instances for each dynamic cluster is reached.
Example
Use the following placement scenarios as a guideline for
your dynamic cluster settings:
- To specify that exactly two servers are started when the dynamic
cluster is running: Click Keep multiple instances started
at all times. Set the Number of instances value
to 2. Click Limit the number of instances that
can start and set the Number of instances value
to 2.
- To limit the number of started servers to five, and to stop the
servers when no activity occurs, click Stop all instances
during periods of inactivity. Set the maximum number of
instances by clicking Limit the number of instances that
can start and set the Number of instances value
to 5.
- To keep at least one instance active at all times, and to support
an unlimited number of instances to start, click Keep one
instance started at all times and Do not limit
the number of instances that can start.
What to do next
Remember: To change your server ports after the server
has been created, you must change the ports on each server instance.
You cannot change the ports through the dynamic cluster template.
Because multiple servers can be on the same node by configuring vertical
stacking, the ports must be unique for each server instance.