Contents

ISS Service - Field Help

Edit any of the following settings on the ISS Service panel and click Update Configuration.

Dispatcher cluster address (local cell only)

The cluster address currently being used by the Dispatcher component. ISS only uses this information when a Dispatcher-type observer is also configured. The configuration file will have default placeholder values that will be ignored by ISS if the service is not associated with a Dispatcher observer. This field is relevant only when a Dispatcher observer is used.

Dispatcher port (local cell only)

The port currently being used by the Dispatcher component. ISS only uses this information when a Dispatcher-type observer is also configured. The configuration file will have default placeholder values that will be ignored by ISS if the service is not associated with a Dispatcher observer. This field is relevant only when a Dispatcher observer is used.

Overflow node (local cell only)

This keyword identifies a server on which to fall back if all the other nodes in the NodeList are unable to provide the service.

Alarm command (local cell only)

Contains a command string to execute if the service runs out of available nodes. The command string is operating-system dependent.

Selection method (local cell only)

This keyword specifies how the ISS Monitor is to select the best node currently able to provide a Service. The selection method may be either ROUNDROBIN, BEST, or STATRR. The default is BEST.

  • ROUNDROBIN: incoming requests are sent to each server in turn. Load calculations are made, but are only used to eliminate nodes that have failed or that exceed their metric limits (and so are considered overloaded). This is the only applicable selection method if any nodes are configured to be Not ISS Agent.

  • BEST: incoming requests during a specific heartbeat interval are sent to the server with the lowest load at the start of that interval. ISS will not recommend a server that has been identified as having failed. This method works well for any duration of the connections, provided the frequency of new connections is low relative to the heartbeat interval. The load values are recalculated after each set of heartbeats per update.

  • STATRR: incoming requests within a heartbeat interval are shared between servers in proportion to their loading. ISS gathers load statistics for all the servers and uses them to build a profile of the most and least heavily loaded servers. The load statistics are recalculated after each set of heartbeats per update. This method works well where there is a high frequency of short-lived connections.



The following information is also displayed on the ISS Service panel:

Service name

The Name of the service to be provided.

DNS name

The DNS Name is a dotted decimal address (for example, www.issdev.hursley.ibm.com) that will be the address clients request when they wish to use a service that ISS is balancing.

Resource List (local cell only)

A list of Resource Types added to this Service.

Interface List (local cell only)

A list of interfaces added to this Service.

NOTES on interfaces to nodes:

You can store as many IP addresses per node as you want. This might be important if you have more than one network adapter in a node, or if you have multiple virtual IP addresses (alias addresses) configured onto a single physical network adapter.

A node can have multiple interfaces, and these interfaces can be listed in the node interface list of services. However, for any given node, each interface must be in the node interface list of a different service. Or, only one interface per node can be in the node interface list of any one service.

Using this mechanism, you could, for example, have three different applications running on a node. Each application is bound to, and accessed via its own interface. Each application corresponds to a service, and each service has one of the interfaces in its node interface list. Multiple such nodes could be configured, and via this configuration, you can load balance between the services of each of them.