Setting Up HTTP Load Balancing

This section describes how to set up load balancing for GlassFish Server.

The following topics are addressed here:

• Prerequisites for Setting Up HTTP Load Balancing

• Procedure for Setting Up HTTP Load Balancing

• HTTP Load Balancer Deployments

Prerequisites for Setting Up HTTP Load Balancing

Before configuring your load balancer, you must:

• Install a supported web server and configure it. For more information on configuring a supported web server, see Chapter 7, Configuring Web Servers for HTTP Load Balancing.

• Install the Loadbalancer Plug-In.

  For complete instructions on installing the Loadbalancer Plug-In, see Chapter 7, Configuring Web Servers for HTTP Load Balancing.

• Create GlassFish Server clusters or server instances to participate in load balancing.

• Deploy applications to these clusters or instances.

Procedure for Setting Up HTTP Load Balancing

There are several asadmin subcommands that enable you to set up and use HTTP load balancing in your GlassFish Server and web server environment.

To Set Up Load Balancing Using the asadmin Tool

Most of the required load balancing configuration settings can be performed in a single step with the asadmin create-http-lb subcommand, as described in this procedure. After performing this procedure, or if you choose to not perform all configuration steps with one subcommand, you can set individual load balancing options using several other subcommands. Information about configuring individual load balancing options is provided after this procedure, in Configuring the HTTP Load Balancer.

1. Create and configure a load balancer.

   Use the asadmin create-http-lb subcommand.

   For the purposes of this procedure, the create-http-lb subcommand can be used to perform the following load balancing tasks. Other options are available but are not included in this example. For more information, see create-http-lb(1).

   • Specify a target cluster or standalone server instance for the load balancer to manage (--target). This task can also be performed at a later time with the create-http-lb-ref(1) subcommand.

   • Enable (activate) load balancing on the specified target (--lbenableallinstances). This task can also be performed at a later time with the enable-http-lb-server(1) subcommand. Note that load balancing is enabled by default for all instances.

   • Enable load balancing for the applications that run on the specified target. The applications must already be deployed and enabled for use on the clusters or standalone instances that the load balancer references (--lbenableallapplications). This task can also be performed at a later time with the enable-http-lb-application(1) subcommand. Note that load balancing is enabled by default for all applications.

   • Create a health checker for the load balancer. A health checker monitors unhealthy server instances so that when they become healthy again, the load balancer can send new requests to them (--healthcheckerurl). This task can also be performed at a later time with the create-http-health-checker(1) subcommand.

   • Generate a load balancer configuration file. This file can be used with the Loadbalancer Plug-In and exported to other targets. (load_balancer_name). This task can also be performed at a later time with the export-http-lb-config(1) subcommand.

2. Copy the load balancer configuration file to your web server config directory where the Loadbalancer Plug-In configuration files are stored.

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   Note - To generate the load balancer configuration file and send the data over the wire to the web server in a single step, you need to configure the web server for SSL setup and import the DAS certificate. The load balancer configuration file can then be pushed using the apply-http-lb-changes(1) subcommand. For information on configuring web servers for HTTP load balancing, see Chapter 7, Configuring Web Servers for HTTP Load Balancing.

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Example 8-1 Creating a Load Balancer

The following example creates a load balancer on a host named host1 using port 5555. A cluster named c1 is the target. A healthchecker is enabled for the load balancer, and a load balancer configuration file named mylb is generated. The following command should be entered on a single line.

asadmin> create-http-lb --devicehost host1 --deviceport 55555 --target c1 
--healthcheckerinterval 10 mylb

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

• Using Multiple Standalone Instances

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 Chapter 9, Upgrading Applications Without Loss of Availability.

Using Multiple Standalone Instances

It is also possible to configure your load balancer to use multiple standalone instances, and load balance and failover requests between them. However, in this configuration, you must manually ensure that the standalone 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.