Amer Networks E5Web GUI - Manual (Page 688)

• SLB can allow network administrators to perform maintenance tasks on servers or
applications without disrupting services. Individual servers can be restarted, upgraded,
removed, or replaced, and new servers and applications can be added or moved without
affecting the rest of a server farm, or taking down applications.
• The combination of network monitoring and distributed load sharing also provides an extra
level of protection against Denial Of Service (DoS) attacks.
SLB Deployment Considerations
The following issues should be considered when deploying SLB:
• Across which servers is the load is to be balanced.
• Which SLB algorithm will be used.
• Will "stickiness" be used.
• Which monitoring method will be used.
Each of these topics is discussed further in the sections that follow.
Identifying the Servers
An important first step in SLB deployment is to identify the servers across which the load is to be
balanced. This might be a server farm which is a cluster of servers set up to work as a single
"virtual server". The servers that are to be treated as a single virtual server by SLB must be
specified.
10.4.2. SLB Distribution Algorithms
There are several ways to determine how a load is shared across a set of servers. cOS Core SLB
supports the following two algorithms for load distribution:
Round-robin The algorithm distributes new incoming connections to a list of servers
on a rotating basis. For the first connection, the algorithm picks a server
randomly, and assigns the connection to it. For subsequent connections,
the algorithm cycles through the server list and redirects the load to
servers in order. Regardless of each server's capability and other aspects,
for instance, the number of existing connections on a server or its
response time, all the available servers take turns in being assigned the
next connection.
This algorithm ensures that all servers receive an equal number of
requests, therefore it is most suited to server farms where all servers
have an equal capacity and the processing loads of all requests are likely
to be similar.
Connection-rate This algorithm considers the number of requests that each server has
been receiving over a certain time period. This time period is known as
the Window Time. SLB sends the next request to the server that has
received the least number of connections during the last Window Time
number of seconds.
The Window Time is a setting that the administrator can change. The
default value is 10 seconds.
Chapter 10: Traffic Management
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