6.5. Clusters
Clusters are defined in two separate sections, AtmPool and VirtualHost. These sections roughly correspond to the `Advanced Traffic Managers' and `Virtual Servers' menus in the tlclbconfig program.
6.5.1. AtmPool Section
The AtmPool section defines the ATMs that will be used to manage the cluster, as well as settings that pertain to the cluster itself. The section begins with the AtmPool keyword and the name of the pool.
AtmPool atmgroup1 AddAtm atm1.turbolinux.usa AddAtm 192.168.1.10 SendArpDelay 20 MaxLostHeartbeats 3 HeartbeatDelay 1 NumConnections 10000 NumServers 1000 NumServices 100 ConnectionTimeout 600 EndAtmPool |
 | Only one ATM pool is currently supported. |
ATMs are added with an AddAtm line, simply specifying the IP address or fully qualified domain name.
In addition to the ATMs themselves, there are several other settings:
- SendArpDelay
Tells how often to send out an ARP broadcast announcing the IP address of the cluster. (Given in seconds.)
- HeartbeatDelay
Specifies how often the primary ATM should send out a heartbeat broadcast so that backup ATMs know it is still alive. (Given in seconds.)
- MaxLostHeartbeats
Tells how many heartbeats a backup ATM can miss before it assumes that the primary ATM has gone down and initiates the process to promote the backup to be the primary ATM.
- ConnectionTimeout
Gives the amount of time to keep an inactive connection open and in the cluster daemon's tables.
You can tune the daemon for a specific maximum number of servers, services, and connections that the cluster will support. Use the NumServers, NumServices, and NumConnections keywords to specify these values. The defaults for these are 1,000 servers, 100 services, and 10,000 connections. It is highly recommended that you configure these to match the needs of your cluster. You can find information on tuning these settings in Chapter 7.
| If the number of connections to your cluster exceeds the maximum specified in the configuration file, all new connections will be dropped. The kernel module creates a table containing only the number of entries that you specify in the configuration file. Be sure to set this value higher than the maximum expected number of concurrent connections. |
6.5.2. VirtualHost Section
The VirtualHost section combines an ATM pool, a server pool, and an IP address. It also allows you to specify the email address of the administrator. The section will look something like this:
VirtualHost 192.168.1.2 AddAtmPool router1 AddServerPool servergroup1 MailTo cluster-admin@mybusiness.org EndVirtualHost |
The IP address is included with the header of the section. This is the virtual IP address you will use to connect to the cluster itself. Anything sent to this IP address will be forwarded to the cluster nodes. The address can be given in dotted decimal or as a domain name. If you use a domain name, make sure it resolves to the appropriate IP address. Also make sure that no other machine has that IP address.
The AddAtmPool specifies the ATMs that are to be used in this cluster. It simply refers to the ATM pool specified in a previous section. Similarly, the AddServerPool specifies the same thing for cluster nodes.
The MailTo parameter is used to send email messages when something goes wrong with the cluster. If you do not specify an email address, no email messages will be sent. Either way, messages will still be logged to the /var/log/clusterserverd.log file. Messages will be sent whenever an ATM, server node, or service goes down. A message will also be sent if there is some other fatal condition, such as the SpeedLink module crashing.
| You can define multiple virtual IP addresses by using multiple VirtualHost sections, but they will have to share the same ATM pool. |