Red Hat CLUSTER SUITE FOR ENTERPRISE LINUX 5.1 Overview page 39

• Round-Robin Scheduling — Distributes each request sequentially around a pool of real
servers. Using this algorithm, all the real servers are treated as equals without regard to
capacity or load.
• Weighted Round-Robin Scheduling — Distributes each request sequentially around a pool of
real servers but gives more jobs to servers with greater capacity. Capacity is indicated by a
user-assigned weight factor, which is then adjusted up or down by dynamic load information.
This is a preferred choice if there are significant differences in the capacity of real servers in a
server pool. However, if the request load varies dramatically, a more heavily weighted server
may answer more than its share of requests.
• Least-Connection — Distributes more requests to real servers with fewer active connections.
This is a type of dynamic scheduling algorithm, making it a better choice if there is a high
degree of variation in the request load. It is best suited for a real server pool where each
server node has roughly the same capacity. If the real servers have varying capabilities,
weighted least-connection scheduling is a better choice.
• Weighted Least-Connections (default) — Distributes more requests to servers with fewer
active connections relative to their capacities. Capacity is indicated by a user-assigned
weight, which is then adjusted up or down by dynamic load information. The addition of
weighting makes this algorithm ideal when the real server pool contains hardware of varying
capacity.
• Locality-Based Least-Connection Scheduling — Distributes more requests to servers with
fewer active connections relative to their destination IPs. This algorithm is for use in a
proxy-cache server cluster. It routes the packets for an IP address to the server for that
address unless that server is above its capacity and has a server in its half load, in which
case it assigns the IP address to the least loaded real server.
• Locality-Based Least-Connection Scheduling with Replication Scheduling — Distributes more
requests to servers with fewer active connections relative to their destination IPs. This
algorithm is also for use in a proxy-cache server cluster. It differs from Locality-Based
Least-Connection Scheduling by mapping the target IP address to a subset of real server
nodes. Requests are then routed to the server in this subset with the lowest number of
connections. If all the nodes for the destination IP are above capacity, it replicates a new
server for that destination IP address by adding the real server with the least connections
from the overall pool of real servers to the subset of real servers for that destination IP. The
most-loaded node is then dropped from the real server subset to prevent over-replication.
• Source Hash Scheduling — Distributes requests to the pool of real servers by looking up the
source IP in a static hash table. This algorithm is for LVS routers with multiple firewalls.
Also, the active LVS router dynamically monitors the overall health of the specific services on
the real servers through simple send/expect scripts. To aid in detecting the health of services
that require dynamic data, such as HTTPS or SSL, you can also call external executables. If a
service on a real server malfunctions, the active LVS router stops sending jobs to that server
until it returns to normal operation.
Two-Tier LVS Topology
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