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.
On the z/OS platform,
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 Servers > Clusters > New.
The Create a new cluster wizard starts.
- Specify a name for the cluster.
Optional: Specify a short name for the
cluster. This field only appears if you are running on a z/OS system. 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 uppercase alphanumeric 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.
Important: If you specify a short name,
make sure that you set up a RACF SERVER class profile that includes this short
name.
- Select Prefer local if you want to enable node-scoped routing
optimization. This option is enabled by default. When this option
is enabled, if possible, EJB requests are routed to the client node. This
option improves performance because client requests are sent to local enterprise
beans.
- 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.
To change these settings
for the replication domain, click Environment > Replication domains > replication_domain_name.
To modify the Web container settings, click Servers > Clusters > cluster_name >
Cluster members > cluster_member_name > Web container settings
> Session management > Distributed environment settings 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 Servers
> Clusters > cluster_name > Cluster members > New.
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, SAF (for example, RACF), started
task control, and others.
- 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]](../../ngzos.gif)
On the z/OS platform, 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 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 the z/OS platform. If some of these ports are already
defined for use elsewhere in your z/OS 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, SAF (for example, RACF), started
task control, and others.
- 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.
- 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 Servers > Clusters,
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 Save. Your
changes are saved and synchronized across all of your nodes.
Avoid trouble: If you click
Save, but do not select Synchronize changes
with Nodes, when you restart the cluster, WebSphere Application Server 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 a configured 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
- Create additional cluster members.
- 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 Servers > Clusters > 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.
- Start the cluster.
- Use scripting to automate the task of creating clusters.