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Chapter 14 Load Balancing in the P333R-LB
54 Avaya P333R-LB User’s Guide
affected. However, the list of cache servers is not restored to its original
configuration. As a result, persistency is only partially recovered.
Weighted Real Servers
You can assign weights to Real Servers (caches) to enable faster servers to receive a
larger share of sessions. This minimizes overloading and maximizes functionality
If you assign a weight to a Real Server, the sessions are distributed to the servers in
the same metric chosen (Hash or MinMiss Hash). However, weighted servers are
assigned a larger share of sessions. For example, if you assign a weight of 100 to one
and do not assign a weight to a second server, the weighted server receives 10
sessions for each session directed to the second server.
Health Check
P333R-LB constantly health-checks the Real Servers to ensure that each Real Server
(in this case, each server) is accessible and operational. A server that fails the health
check is automatically removed from the load balancer’s internal list of currently
available servers.
P333R-LB supports the following health-check methods:
• ICMP Echo - Each server is periodically pinged and checked if an answer was
received.
• TCP Port Checking - A TCP connection is periodically opened to every server,
checking for successful completion of the connection.
• HTTP Server Checking - Useful for web applications, this method enables
verifying HTTP server functioning by comparing the response from the server
with a complete sample of the web page. P333R-LB sends a request to the HTTP
server to simulate an outside request. P333R-LB compares the server’s response
with the sample to ascertain the level that the HTTP server is functioning.
P333R-LB supports the following HTTP retrieving methods:
— Head - Retrieve only the HTTP headers without document body content.
This is the default method.
— Get - Retrieve all data from the HTTP server.
P333R-LB supports the following responses:
— Any response - P333R-LB assumes the server is functional when P333R-LB
receives any response.
— Any OK response - P333R-LB assumes the server is functional when the
server’s response is one of the HTTP OK responses (codes 201-204).
— Exact OK response - P333R-LB assumes the server is functional only when
P333R-LB receives the exact response expected (code 200). This is the
default method.