Technical data

108 Brocade ServerIron ADX Advanced Server Load Balancing Guide

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Sample configurations

Asymmetric TCS (FastCache)

Traffic in typical TCS configurations passes through the ServerIron ADX both from the client to the

cache and from the cache to the client. The ServerIron ADX uses the cache responses to the client

to diagnose the health of the cache server.

If the cache server responds to the client requests the ServerIron ADX redirects to the cache server,

the ServerIron ADX knows that the cache server is healthy. However, if the cache server stops

sending replies to the client requests, the ServerIron ADX assumes that the cache server is down

and stops redirecting requests to that cache server.

Some configurations are asymmetric— traffic from the cache server to the client does not pass

back through the ServerIron ADX. For example, caches that support multiple NICs might at the

same time support only one default gateway. Figure 25 shows a configuration in which a cache

server’s default gateway is configured to go to the customer access router (RAS) instead of the

ServerIron ADX. In this configuration, the ServerIron ADX does not see cache responses to client

requests. Because the ServerIron ADX does not see responses coming from the cache server, the

ServerIron ADX assumes that the cache server is down and stops redirecting requests to that

cache server.

You can override this behavior by enabling the FastCache feature. This feature configures the

ServerIron ADX to continue redirecting client requests to a cache server even though the ServerIron

ADX does not see responses from the cache server. You enable the feature individually for real

servers.

NOTE

Even when use the FastCache feature, the ServerIron ADX still performs a Layer 3 health check by

regularly pinging the cache server. In addition, you can continue to use HTTP health checking.