4.3. Services
The first set of options that you will want to configure are the network services that will be running on your cluster. To do so, choose the `Clustered Services' menu item from the main menu of the configuration tool. From here, you will have two pieces to configure: service agents and the services themselves. We'll take a look at each of these in this section.
 | Before configuring your cluster, please ensure your network's DNS system is working properly. |
4.3.1. Agents
An Application Stability Agent (ASA) monitors the health of a particular service on the cluster nodes.
Several programs have been supplied with Turbolinux Cluster LoadBalancer 10 to perform the ASA checks for you. These programs have names ending with "Agent". See Chapter 8 for a complete list of these agent programs. That chapter also contains extended information about the ASA programs and up/down scripts, including the command-line arguments that they are called with.
| There are three pre-defined ASAs that do not need to be configured in the Application Stability Agents menu. These are `http', `connect', and `none'. The `http' ASA checks HTTP 1.1 servers. The `connect' ASA tests a simple TCP connection. The `none' setting skips the ASA check altogether; the ATM assumes that the service is always up. These three ASAs may be sufficient for your cluster. |
To set up an agent, follow these steps:
From the tlclbconfig main menu, choose `Clustered Services'.
Choose `Application Stability Agents' from the next menu. Here you will see listed all the currently configured stability agents. If you do not have service agents configured initially, you will not see a list in the window.
From this menu, you can add a new ASA or edit an existing one. You can also remove an agent.
To add an ASA, click `Add'.
Enter the following information as requested.
The `Application Stability Agent name' is just a name that will be used later to refer to the ASA. It is best to use the name of the service or something similar.
The `Check with' field specifies the program that will be used to perform the ASA service check. Be sure to include the full path to the program.
The `Event triggered when down' and `Event triggered when up' fields allow you to have a program run when the ASA determines that the service has gone down or come back up. These are not used in most situations, so you can leave them blank. If you do use them, be sure to specify the full path.
One instance in which you would use a `down' script is if you have some way of restarting the service. The `down' script can perform whatever is necessary to try to revive the service.
When you have entered the required information, click `OK' to return to the list of ASAs.
When you are finished entering all the Application Stability Agents that you will need, click `Done'.
4.3.2. Service Settings
Turbolinux Cluster LoadBalancer 10 is a service-oriented cluster. You will need to configure each service so the cluster knows which port numbers to listen on and how to handle incoming connections.
To set up a service, follow these steps:
From the tlclbconfig main menu, choose `Clustered Services'.
Choose `Service Settings' from the `Clustered Services' menu. Here you will see listed all the currently configured services, along with some information about each one. If you don't have services configured initially, you will not see a list in the window.
The name of each service will be shown, along with the port number and whether it is a TCP or UDP port. There may be a flag indicating that the service is configured to be persistent (`sticky') or to fail-over instead of load balance. Finally, the name of the ASA used by the service will be shown.
From this menu, you can add a new service or edit an existing one. You can also remove an existing service.
To add a service, click `Add'.
Enter the following information as requested.
In the `Service name' field, enter the name by which you want to refer to the service. It is best if you use a standard name, such as "http" or "ftp".
In the `Port number' field, enter the port number that the service runs on. If you are not sure what port number a given service should run on, check the /etc/services file. Note that services do not have to run on their default ports. For instance, some web servers run on port 8080, while the default for HTTP is port 80.
Choose whether the service uses the TCP or UDP `Protocol.' Most services use TCP. One notable exception that uses UDP is DNS. This information can also be found in /etc/services.
Choose a `Stability Agent' from the list. If you do not see the ASA you are looking for try scrolling through the list. Also make sure that the ASA was defined per the directions in the previous section.
For most services, you will want to `Load Balance' the workload between all the boxes configured to support the service. If you would like to implement fail-over instead of load balancing, check the `Failover' box.
The final choice you have to make is whether the service should `Allow Session Persistency'. If this option is enabled, new connections coming from clients that already have existing connections will be sent to the same server. This is useful with services using SSL, such as Secure HTTP (HTTPS), because they would otherwise require the client to send authentication information to each server that they ended up accessing.
When you have filled in the service settings, click `OK'.
When you have added all the services that you want to run on the cluster, click `Done'.