Radware Alteon Application Manual page 182

Alteon Application Switch Operating System Application Guide
Server Load Balancing
Persistent Hash
The phash metric provides the best features of hash and minmisses metrics together. This metric
provides stable server assignments like the minmiss metric and even load distribution like the hash
metric.
When you select the phash metric for a group, a baseline hash is assumed based on the configured
real servers that are enabled for the group. If the server selected from this baseline hash is
unavailable, then the old hash metric is used to find an available server.
If all the servers are available, then phash operates exactly like hash. When a configured server
becomes unavailable, clients bound to operational servers will continue to be bound to the same
servers for future sessions and clients bound to unavailable servers are rehashed to an operational
server using the old hash metric.
When more servers go down with phash, you will not have an even load distribution as you would
with the standard hash metric.
Tunable Hash
By default, the hash metric uses the client's source IP address as the parameter for directing a client
request to a real server. In environments where multiple users are sharing the same proxy, resulting
in the same source IP address, a load-balancing hash on the source IP address directs all users to
the same real server.
Tunable hash allows the user to select the parameters (source IP, or source IP and source port) that
are used when hashing is chosen as the load-balancing metric.
Weighted Hash
Weighted hash allows real server weighting to be used in conjunction with the hash load balancing
algorithm. If the configured real server weight is greater than 1, the real server weight is taken into
account during the load-balancing calculation. There are no CLI commands to configure or change
the weighted hash state.
Least Connections
The default metric is leastconns. With the leastconns metric, the number of connections currently
open on each real server is measured in real time. The server with the fewest current connections is
considered to be the best choice for the next client connection request.
This option is the most self-regulating, with the fastest servers typically getting the most
connections over time.
Least Connections Per Service
The svcleast (least connections per service) metric is an extension of the leastconns metric. When
using this metric, Alteon selects the real server based only on the number of active connections for
the service which is load balanced, and not the total number of connections active on the server. For
example, when selecting a real server for a new HTTP session, a real server serving one HTTP
connection and 20 FTP connections takes precedence over a real server serving two HTTP
connections only.
Round-Robin
With the roundrobin metric, new connections are issued to each server in turn. This means that the
first real server in the group gets the first connection, the second real server gets the next
connection, followed by the third real server, and so on. When all the real servers in this group have
received at least one connection, the issuing process starts over with the first real server.
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Document ID: RDWR-ALOS-V2900_AG1302