A cluster is a set of application servers that you manage
together as a way to balance workload.
Before you begin
Before you create a cluster:
- Review the content of the topic "Clusters and workload management",
especially the information about setting cluster weights.
- Decide if you want enterprise bean requests routed to the node
on which the client resides.
- Decide if you want to use HTTP memory-to-memory replication.
- Determine the appropriate configuration settings for the first
cluster member. A copy of the first cluster member that you create
is stored as part of the cluster data and becomes the template for
all additional cluster members that you create.
- Decide on which node you want the first cluster member to reside.
About this task
You might want to create a cluster if you need to:
- Balance your client requests across multiple application servers.
- Provide a highly available environment for your applications.
A cluster enables you to manage a group of application
servers as a single unit, and distribute client requests among the
application servers that are members of the cluster.
If you plan to create a cluster of servers that spans
multiple systems in a sysplex and has stateful session beans with
an activation policy of Transaction deployed in them, the passivation
directory should reside on an HFS (hierarchical file system) that
is shared across the multiple systems in the sysplex on which the
clustered servers are running.
To create a cluster:
Procedure
- In the administrative console, click . The Create a new cluster wizard starts.
- Specify a name for the cluster.
Optional: Specify a short name
for the cluster. For clustered servers, the WLM application
environment is the default value for the cluster short name. If you
specify a short name for a cluster, the name:
- Must be one to eight characters in length.
- Must contain only alpha-numeric or national language characters.
- Cannot start with a number.
- Must be unique in the cell.
- Cannot be the same as the value specified on the ClusterTransitionName custom
property of any non-clustered server. Do not specify a cluster transition
name for a server that is part of a cluster.
Avoid trouble: If you specify a short
name, make sure that you set up a RACF® SERVER
class profile that includes this short name.
gotcha
- Select Prefer local if you want to enable host-scoped
routing optimization. This option is enabled by default.
When this option is enabled, if possible, EJB requests are routed
to the client host. This option improves performance because client
requests are sent to local enterprise beans.
Supported configurations: If you enable the preferLocal
optimization, the deployment manager must be running to affect the
configuration. If the deployment manager is shut down, preferLocal
optimization is not performed and requests might be dispersed across
all the members of the cluster.
sptcfg
- Select Configure HTTP session memory-to-memory replication if
you want a memory-to-memory replication domain created for this cluster. The replication domain is given the same name as the cluster
and is configured with the default settings for a replication domain.
When the default settings are in effect, a single replica is created
for each piece of data and encryption is disabled. Also, the web container
for each cluster member is configured for memory-to-memory replication.
If
the WAS cluster has session Memory to Memory replication enabled,
then the plug-in configuration file for that server cluster must have
the GetDWLMTable property set to true.
To change these settings
for the replication domain, click replication_domain_name.
To modify the web container settings, click cluster_name cluster_member_name.
Then, in the Container settings section, click in the
administrative console. If you change these settings for one cluster
member, you might also need to change them for the other members of
this cluster.
- Click Next.
- Choose whether to create an empty cluster or to create
the first member of the cluster.
If you decide to create
an empty cluster, to add members to this cluster, in the administrative
console, click cluster_name.
To
create an empty cluster:
- Select None. Create an empty cluster.
- Click Next to display a summary of the defined
cluster.
- Click Finish to create the cluster, or click Cancel if
you decide not to create this cluster.
When you create the first cluster member, remember that a
copy of the first cluster member that you create is stored as part
of the cluster data and becomes the template for all additional cluster
members that you create.
- Specify the name of the first cluster member.
- Select the node on which you want this cluster member
to reside.
Specify a short name for this cluster
member. The short name is the default z/OS® job name and identifies the cluster member
to the native facilities of the operating system, such as Workload
Manager (WLM), Automatic Restart Manager, and RACF.
- Specify the weight value for the cluster member. The weight value controls the amount of work that is directed
to the application server. If the weight value for this server is
greater than the weight values that are assigned to other servers
in the cluster, then this server receives a larger share of the workload.
The weight value represents a relative proportion of the workload
that is assigned to a particular application server. The value can
range from 0 to 20.
![[z/OS]](../images/ngzos.gif)
On z/OS,
weight is used to balance some of the workload types, but others are
balanced by the z/OS system.
- For HTTP requests, weights are used to distribute HTTP traffic
between the web server plug-in and the controller handling the clustered
application server. Assign a higher weight value to the application
server that should receive the HTTP traffic.
- For web services calls, information is transferred from a servant
in one application server to a controller in another application server.
The application server that receives the call has the highest weight
value.
- Weight has no affect on Internet Inter-ORB Protocol (IIOP) requests.
IIOP requests are distributed to the correct application server using
the sysplex distributor.
- Select Generate unique HTTP ports if you want
to generate unique port numbers for every HTTP transport that is defined
in the source server. When this option is selected, which
is the default setting, this cluster member does not have HTTP transports
or HTTP transport channels that conflict with any of the other servers
that are defined on the same node. If you unselect this option, all
of the cluster members will share the same HTTP ports.
- Select the core group to which you want this cluster
member to belong. You are prompted for the core group only
if you have more than one core group defined for this cluster.
- Select one of the following options to determine how
the server resources are promoted in the cluster.
- Cluster to move the resources of the first
cluster member to the cluster level. The resources of the first cluster
member replace the resources of the cluster.
- Server to maintain the server resources
at the new cluster member level. The cluster resources remain unchanged.
- Both to copy the resources of the cluster
member (server) to the cluster level. The resources of the first cluster
member replace the resources of the cluster. The same resources exist
at both the cluster and cluster member scopes.
- Select one of the following options as the basis for
the first cluster member.
- Create the member using an application server template.
If you select the defaultZOS template, which
is the only one that is listed unless you used the createServerTemplate command
for the AdminTask object to create additional templates, the first
cluster member uses the default port assignments for z/OS. If some of these ports are already defined
for use elsewhere in your system, your newly created cluster member
might not start, might function incorrectly, or might generate unexpected
error messages. Therefore, you must resolve any port conflicts before
you start this server.
- Create the member using an existing application server as a template.
- Create the member by converting an existing application server.
Avoid trouble: You can only add an existing
application server to the cluster if you select that server as the
first cluster member. You cannot add other existing application servers
to that cluster after you create the first cluster member. If you
add an existing server to a cluster, the only way to remove that server
from the cluster is to delete the server. Therefore, you might want
to use the existing server as a template for the first cluster member
instead of as the cluster member. If you keep the original application
server out of the cluster, you can reuse that server as the template
if you need to rebuild the configuration.
gotcha
- Click Next.
- Create additional cluster members. Before you
create additional cluster members, check the configuration settings
of the first cluster member. These settings are displayed at the bottom
of the Create additional cluster members panel of the Create a new
cluster wizard. For each additional member that you want to create:
- Specify a unique name for the member. The
name must be unique within the node.
- Select the node to which you want to assign the cluster
member.
- Specify the weight you want given to this member. The weight value controls the amount of work that is directed
to the application server. If the weight value for the server is greater
than the weight values that are assigned to other servers in the cluster,
then the server receives a larger share of the workload. The value
can range from 0 to 20.
Specify a short name for this cluster
member. The short name is the default z/OS job name and identifies the cluster member
to the native facilities of the operating system, such as Workload
Manager (WLM), Automatic Restart Manager, and RACF.
- Select Generate unique HTTP ports if you want
to generate unique port numbers for every HTTP transport that is defined
in the source server.
- Click Add member. You can edit the
configuration settings of any of the newly created cluster members
other than the first cluster member, or you can create additional
cluster members. Click Previous to edit the properties of the
first cluster member. The settings for the first cluster member become
the settings for the cluster member template that is automatically
created when you create the first cluster member.
- When you finish creating cluster members, click Next.
- View the summary of the cluster and then click Finish to
create the cluster, click Previous to return to the previous
wizard panel and change the cluster, or click Cancel to exit
the wizard without creating the cluster.
- To further configure a cluster, click , and then click the name
of the cluster. Only the Configuration and Local
Topology tabs appear until you save your changes.
- Click Review to review your cluster configuration
settings. Repeat the previous step if you need to make
additional configuration changes.
- If you do not want to make any additional configuration
changes, select Synchronize changes with Nodes and then click . Your changes
are saved and synchronized across all of your nodes.
Avoid trouble: If you click , but do not select Synchronize changes with Nodes,
when you restart the cluster, the product does not start the cluster
servers because it cannot find them on the node. If you want to always
synchronize your configuration changes across your nodes, you can
select Synchronize changes with Nodes as one of your console preferences.
gotcha
- Restart the cluster.
Results
You have created a cluster to which you can assign work requests.
The
Runtime and
Local Topology tabs appear the next
time you access this page.
What to do next
- You can click cluster_name in the
administrative console, and then click the name of a cluster member
to view all of the configuration settings for this cluster member.
You can then use this page to change some of the configuration settings
for the selected cluster member.
For example, if you do not need
to have all of the cluster member components start during the cluster
startup process, you might want to reconfigure the cluster members,
such that the
Start components as needed is selected. This
option is not selected when a new cluster member is created. Selecting
this option can improve cluster startup time, and reduce the memory
footprint of the cluster members.
Avoid trouble: Before
selecting this option, verify that any other WebSphere® products, that you are running
in conjunction with this product, support this functionality.
gotcha
Deprecated feature: The default addressing
mode for a new server is 64-bit. You can deselect the Run in 64-bit
mode field if you need to use 31-bit addressing mode. However, support
for running a server in 31-bit mode is deprecated.
depfeat
- Use the administrative console to view or change the configuration
settings for a cluster. For example, if you are running in a high
availability environment, you can click cluster_name, and then select the Enable
failover of transaction log recovery option for this cluster.
This option allows the recovery of transactions to failover from
one cluster member to another.
- Create additional cluster members.
If
you create a cluster member by converting an existing application
server that is a member of a bus, you must migrate the messaging engine
in the server to the scope of a cluster. To do this, use the wsadmin
command migrateServerMEtoCluster. Do not delete the messaging engine
at server scope and recreate it a cluster scope, because those actions
prevent the messaging engine from working with previously configured
destinations.
- Start the cluster.
- Use scripting to automate the task of creating clusters.
- Create a static routing table to temporarily handle IIOP routing
for the cluster if your high availability infrastructure is disabled.