When you create a dynamic cluster, the workload of the cluster members is dynamically
balanced based on performance information collected from the cluster members. Creating dynamic
clusters enables application server virtualization.
Before you begin
Complete the following prerequisites before creating a dynamic cluster:
- 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, read about 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. For more information, read about configuring vertical stacking.
- If you are creating a dynamic cluster of externally created middleware servers with assisted
life-cycle management, create representations of these servers in the product environment before you
create a dynamic cluster. All of these servers must have the same applications installed and have
the same version of middleware software installed. For more information, read about adding assisted
life-cycle middleware servers.
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.
Procedure
- Create the dynamic cluster.
In the administrative console, click
.
- Select the dynamic cluster server type.
The dynamic cluster server type
determines the type of servers that are members of this dynamic cluster. Depending on the type, you
enter the name of the dynamic cluster on this panel or when you select the membership
method.
- For some dynamic cluster types, you can select the membership method.
The
membership method defines how servers join the dynamic cluster as cluster instances.
Option |
Description |
Automatically define cluster members with rules |
You can Automatically define cluster members with rules if you are
using servers with complete life-cycle management. With this option, you create a membership policy
that defines the nodes on which cluster instances can be placed. |
Manually define cluster members |
If you are using servers with assisted life-cycle management, you can Manually
define cluster members. With this option, you select existing servers to add to the
dynamic cluster. The servers that you select must be homogenous: that is, they must be of the same
server type, middleware server version, and have the same applications installed. Avoid trouble: To add a new middleware server to an existing dynamic cluster when one or
more applications are targeted to the dynamic cluster, you must install the applications on the
middleware server and target the applications to the server before you add the server as member of
the dynamic cluster.
|
- Define the dynamic cluster members.
- If you selected Automatically define cluster members with rules in
the previous step, use the subexpression builder to build a membership policy expression for your
dynamic cluster. This expression is compared to all the nodes in the cell, selecting any nodes for
which the subexpression is true.
- If you selected Manually define cluster members, the action you take
depends on what kind of servers are in your dynamic cluster.
- If your server type is application server, choose an existing static cluster to convert to a
dynamic cluster.
- If your server type is an externally created middleware server with assisted life-cycle
management, select servers from the list, and add them to your dynamic cluster. Before you add
assisted life-cycle servers, be sure that they are the same type, middleware server version, and
have the same set of applications installed.
Avoid trouble: Before you
can add a new middleware server to an existing dynamic cluster when one or more applications are
targeted to the dynamic cluster, you must install the applications on the middleware server and
target the applications to the server.
- Deploy your unmanaged application to the middleware server. For more information read about
deploying unmanaged Web applications.
- Define the deployment target for the application. In the administrative console, click
. Select the target and click Add.
- Click Apply and save your changes.
- Select a dynamic cluster server template.
You can select a dynamic cluster server template only for dynamic clusters that consist of
servers with complete life-cycle management. You can choose an existing predefined template, or
create your own server templates to use when you create your dynamic cluster. Read about creating
server templates.
Avoid trouble: If your configuration consists of mixed versions of
WebSphere® Application
Server Network Deployment, specifically the deployment manager is at a higher
version than the version of the node, you cannot use a predefined server template to create a
dynamic cluster. If you are running a Version 6.1 node and a Version 7.0 deployment manager, for
example, you can create a static cluster of servers on the node, and then convert the static cluster
to a dynamic cluster.
Deprecated feature: The defaultXD
and
defaultXDZOS
server templates that are used when creating a dynamic cluster are
deprecated. Use the default
or defaultZOS
server template
instead.
- 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. If a minimum value is
excessive, performance degradation might occur.
- 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.
- Specify an isolation preference for the dynamic cluster.
- Confirm the dynamic cluster creation.
Click 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 Intelligent Management
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. For more
information read about application placement custom properties.
Results
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.