Figure 14-13 shows how requests coming in from various
clients can be load balanced (or distributed) to various
servers.
Figure 14-13 Load Balancing
Load balancing uses algorithms such as the following:
Round-robin: Selects servers in turn
Least connected: Selects the server with the lowest number of
connections; this is recommended for more extended sessions
Source/IP-hash: Chooses a server based on a hash of the source IP
Cookie marking: Adds a field in the HTTP cookies, which could be
used for decision making
Consistent IP-hash: Adds and removes servers without alarming
cached items or session persistenceA reverse proxy accepts a request from a user, forwards it
to a server that can fulfill it, and returns the server’s
response to the client. A reverse proxy can include some
or all of the following functionality:
Security: The web servers or application servers are not visible from
the external network, so malicious clients cannot access them directly
to exploit any vulnerabilities. Many reverse proxy servers include
features that help protect backend servers from distributed denial-of-
service (DDoS) attacks—for example, by rejecting traffic from particular
client IP addresses (blacklisting) or limiting the number of connections
accepted from each client.