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Distributes requests to the pool of real servers by looking up the source IP in a static hash
table. This algorithm is designed for LVS routers with multiple firewalls.
3.2. Server Weight and Scheduling
The administrator of LVS can assign a weight to each node in the real server pool. This weight
is an integer value which is factored into any weight-aware scheduling algorithms (such as
weighted least-connections) and helps the LVS router more evenly load hardware with different
capabilities.
Weights work as a ratio relative to one another. For instance, if one real server has a weight of 1
and the other server has a weight of 5, then the server with a weight of 5 gets 5 connections for
every 1 connection the other server gets. The default value for a real server weight is 1.
Although adding weight to varying hardware configurations in a real server pool can help
load-balance the cluster more efficiently, it can cause temporary imbalances when a real server
is introduced to the real server pool and the virtual server is scheduled using weighted
least-connections. For example, suppose there are three servers in the real server pool. Servers
A and B are weighted at 1 and the third, server C, is weighted at 2. If server C goes down for
any reason, servers A and B evenly distributes the abandoned load. However, once server C
comes back online, the LVS router sees it has zero connections and floods the server with all
incoming requests until it is on par with servers A and B.
To prevent this phenomenon, administrators can make the virtual server a quiesce server —
anytime a new real server node comes online, the least-connections table is reset to zero and
the LVS router routes requests as if all the real servers were newly added to the cluster.
4. Routing Methods
Red Hat Enterprise Linux uses Network Address Translation or NAT routing for LVS, which
allows the administrator tremendous flexibility when utilizing available hardware and integrating
the LVS into an existing network.
4.1. NAT Routing
Figure 1.3, "LVS Implemented with NAT
requests between the Internet and a private network.
Routing", illustrates LVS utilizing NAT routing to move
Server Weight and Scheduling
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