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Setting Up HTTP Load Balancing
This section describes how to set up the load balancer plug-in and includes
the following sections:
Prerequisites for Setting Up Load Balancing
Before configuring your load balancer, you must:
Note –
If you have a deployment scenario where the Application Server
instances and the load balancer are installed on different network domains,
then you must create the node agent by specifying the fully qualified domain
name using the option, --agentproperties.
For example, asadmin create-node-agent --agentproperties remoteclientaddress=machine1.server.example.com
test-na. For more information about this command, see create-node-agent(1).
Procedure to Set Up Load Balancing
Use the Admin Console GUI or the asadmin tool
to configure load balancing in your environment. The following sections provide
you more information.
 To Set Up Load Balancing Using the Admin Console
-
Create a load balancer configuration.
In the Admin
Console, on the left frame, click HTTP Load Balancers and then click New.
In the New HTTP Load Balancer page, provide the device details and also select
the target cluster or instances.
-
Add a reference to a cluster or stand-alone server instance for
the load balancer to manage.
To do this using the Admin Console,
on the left frame, click the HTTP Load Balancers node and then click the
desired load balancer listed under the node. Open the Targets tab, click
Manage Targets and in the Manage Targets page, select the required target.
If you created the load balancer configuration with a target, and that
target is the only cluster or stand-alone server instance the load balancer
references, skip this step.
-
Enable the cluster or stand-alone server instance referenced by
the load balancer.
To enable a stand-alone server instance using
the Admin Console, on the left frame, click the HTTP Load Balancers node and
then click the desired load balancer listed under the node. Open the Targets
tab and in the Targets table, click the check box next to the instance you
want to enable and click Enable.
To enable a server instance
in a cluster, select the load balancer as explained above and in the Targets
tab, click the desired cluster. Now open the Instances tab, select the desired
instance, and from the Load Balancer Actions drop down list, select Enable
Load Balancing.
The equivalent command to enable a cluster or
a stand-alone instance is asadmin enable-http-lb-server.
-
Enable applications for load balancing.
To do this
using the Admin Console, open the Targets tab as mentioned above and click
the required cluster. Now, open the Applications tab, select the required
application and from the More Actions drop-down list, and select Load Balancer
Enable.
These applications must already be deployed and enabled
for use on the clusters or stand-alone instances that the load balancer references.
Enabling applications for load balancing is a separate step from enabling
them for use.
-
Create a health checker.
To do this using the Admin
Console, open the Targets tab for the load balancer as mentioned in the previous
step and in the Targets table, click Edit Health Checker.
The
health checker monitors unhealthy server instances so that when they become
healthy again, the load balancer can send new requests to them.
Note –
If you are using Sun Java System Web Server (6.1 or 7.0), instead
of performing steps 6 and 7, you can generate the load balancer configuration
file and send the data over the wire to the Web Server in a single step.
To do this using the Admin Console, click the desired load balancer
and then open the Export tab. In this tab, click Apply Changes Now. This sends
the data to the Web Server configuration directory.
-
Generate the load balancer configuration file.
To
do this using the Admin Console, click the load balancer and then open the
Export tab. In this tab, click Export Now.
This command generates
a configuration file to use with the load balancer plug-in shipped with the Sun Java System Application Server.
-
Copy the load balancer configuration file to your web server config directory where the load balancer plug-in configuration files
are stored.
Note –
To generate the load balancer configuration file automatically
and send the data over the wire to the Web Server in a single step, you need
to configure Web server for SSL setup and import the DAS certificate. For
information on configuring Sun Java System Web Server, see Configuring Sun Java System Web Server.
To Set Up Load Balancing Using the asadmin Tool
-
Create a load balancer configuration.
To do this,
use the command, asadmin create-http-lb-config.
Note –
You can perform all the following steps (Step 2 through Step 7)
using a single asadmin command, create-http-lb and
its options. For more information about this command, see create-http-lb(1).
-
Add a reference to a cluster or stand-alone server instance for
the load balancer to manage.
To do this, use the command, asadmin
create-http-lb-ref. For more information about this command, see create-http-lb-ref(1).
If you created the load balancer configuration
with a target, and that target is the only cluster or stand-alone server instance
the load balancer references, skip this step.
-
Enable the cluster or stand-alone server instance referenced by
the load balancer.
To do this, use the command asadmin
enable-http-lb-server. For more information about this command,
see enable-http-lb-server(1).
-
Enable applications for load balancing.
To do this,
use the command asadmin enable-http-lb-application. For
more information about this command, see enable-http-lb-application(1).
These
applications must already be deployed and enabled for use on the clusters
or stand-alone instances that the load balancer references. Enabling applications
for load balancing is a separate step from enabling them for use.
-
Create a health checker.
To do this, use the command, asadmin create-http-health-checker. For more information about this
command, see create-http-health-checker(1).
The
health checker monitors unhealthy server instances so that when they become
healthy again, the load balancer can send new requests to them.
Note –
If you are using Sun Java System Web Server (6.1 or 7.0), instead
of performing steps 6 and 7, you can generate the load balancer configuration
file and send the data over the wire to the Web Server in a single step.
To do this using the asadmin tool, set the --autoapplyenabled option of the create-http-lb command to true. For more information about
this command, see create-http-lb(1).
-
Generate the load balancer configuration file.
To
do this, use the command asadmin export-http-lb-config.
For more information about this command, see export-http-lb-config(1). This command
generates a configuration file to use with the load balancer plug-in shipped
with the Sun Java System Application Server.
-
Copy the load balancer configuration file to your web server config directory where the load balancer plug-in configuration files
are stored.
Note –
To generate the load balancer configuration file automatically
and send the data over the wire to the Web Server in a single step, you need
to configure Web server for SSL setup and import the DAS certificate. For
information on configuring Sun Java System Web Server, see Configuring Sun Java System Web Server.
HTTP Load Balancer Deployments
You can configure your load balancer in different ways, depending on
your goals and environment, as described in the following sections:
Using Clustered Server Instances
The most common way to deploy the load balancer is with a cluster or
clusters of server instances. By default all the instances in a cluster have
the same configuration and the same applications deployed to them. The load
balancer distributes the workload between the server instances and requests
fail over from an unhealthy instance to a healthy one. If you’ve configured
HTTP session persistence, session information persists when the request is
failed over.
If you have multiple clusters, requests can be load balanced across
clusters but are only failed over between the instances in a single cluster.
Use multiple clusters in a load balancer to easily enable rolling upgrades
of applications. For more information, see Upgrading Applications Without Loss of Availability.
Note –
Requests cannot be load balanced across clusters and stand-alone
instances.
Using Multiple Stand-Alone Instances
It is also possible to configure your load balancer to use multiple
stand-alone instances, and load balance and failover requests between them.
However, in this configuration, you must manually ensure that the stand-alone
instances have homogenous environments and the same applications deployed
to them. Because clusters automatically maintain a homogenous environment,
for most situations it is better and easier to use clusters.
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