Compaq AA-Q88CE-TE manual Router Load Balancing, Example 2-5 Configuration of Callout Servers

Starting and Setting Up RTR 2.5 Setting up Callout Servers

Example 2–5 Configuration of Callout Servers

% rtr

RTR> set environment/node= -

_RTR> (FE1,FE2,FE3,TR1,TR2,BE1,BE2,BE3)

RTR> start rtr

RTR> create facility funds_transfer/frontend=(FE1,FE2,FE3) -

_RTR>	/router=(TR1,TR2) -
_RTR>	/backend=(BE1,BE2,BE3) -
_RTR>	/call_out=router

2.6 Router Load Balancing

Router load balancing, or intelligent re-connection of frontends to a router is possible, allowing a frontend to select the router that has least loading. The create facility and set facility commands have the /balance qualifier to control this. RTR now allows frontends to determine their router connection. The RTR version 2 implementation of load balancing treated all routers as equal and this could cause reconnection timeouts in geographically distant routers.

When used with create facility, /balance specifies that load balancing is enabled for frontend/router connections across the facility.

Use the set facility/[no]balance to switch load-balancing off and on.

The default behavior (/nobalance) is for a frontend to connect to the preferred router. Preferred routers are selected in the order specified in the create facility/router=tr1,tr2,tr3.. qualifier. Automatic failback ensures that the frontend will reconnect to the first router in the order when it becomes available. Manual balancing can be attained by specifying different router orders across the frontends.

Non load-balanced frontend connections will fail back to the preferred router when it becomes available.

Automatic load balancing institutes a router list with a random value for the frontend assigned at the time the create facility with the /balance command is issued. The frontend will sort the list of routers based on its own random order. Randomness ensures that there will be a balance of load in a configuration with a large number of frontends. Automatic failback will maintain the load distribution on the routers and failback is controlled at a limited rate so as not to overload configurations with a small number of routers.

The following points should be born in mind when using load-balancing:

•Frontends connect to a single router, per facility

•When several routers are configured on the frontend:

The specified list in the create facility constitutes the preferred search order, by default, unless /balanced is used

•Balancing may be individually enabled or disabled on the frontend nodes.

•Balancing is dynamic. The loss or addition of a router node causes the frontend nodes to redistribute their connections.

2–8Starting and Setting Up RTR