Technical data

ServerIron ADX Advanced Server Load Balancing Guide 87
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Traffic distribution based on cache server capacity
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ServerIron ADX supports multiple pattern search for the same rule. Support is provided for up to 4
different pattern strings as shown in the following example.
Force rehash
By default, the following will happen when the cache server goes down and goes up again:
• When the cache server goes down, its hash bucket will be taken by other active cache server.
• When a failed cache server comes up, the hash bucket will be allocated if, and only if, there
are hash buckets without server association. In most cases, where traffic is evenly spread,
none of the hash buckets will be available to the new server.
When a cache server goes down and up, the group hash table is not rehashed and the other server
won't be affected. This will make the ServerIron ADX maintain the persistence of the cache servers.
Though in a situation where all of the hash table entries are taken by other cache servers, the
failed cache server may not be able to process traffic after it comes back to active. This also
applies to the situation that the new cache server is added to the group.
You can configure the entire hash table to be re-hashed when a new cache server is added or a
failed cache server recovers. Use the csw-force-rehash command within the cache group
configuration to enable automatic rehash of hash buckets.
ServerIronADX(config)# server cache-group 1
ServerIronADX(config-tc-1)# csw-force-rehash
Syntax: [no] csw-force-rehash
NOTE
This command generally disrupts the existing cache persistence.
Traffic distribution based on cache server capacity
In order to determine the health of a cache server, the Brocade ServerIron ADX performs basic
health monitoring functions such as check IP connectivity and check reachability of application
ports. Basic monitoring of these metrics however, may not provide an aggregated view of the health
of cache servers. Brocade ServerIron ADX utilizes an advanced capacity check mechanism for Blue
Coat CacheFlow servers by polling the state of Blue Coat servers through SNMP.
The above mentioned capacity check feature is available with Layer-4 switching of TCS traffic.
Starting release 12.4.00a release, it can also be enabled in environments where Brocade
ServerIron ADX is configured for cache selection through application-specific Layer-7 rules.
ServerIronADX(config)# csw-policy p1
ServerIronADX(config-csw-p1)# match r1 forward 10
ServerIronADX(config-csw-p1)# match r1 hash-persist url search-url “v1” offset 0
ServerIronADX(config-csw-p1)# match r1 hash-persist url search-url “v2” offset 0
ServerIronADX(config-csw-p1)# match r1 hash-persist url search-url “v3” offset 0
delimiter “&”
ServerIronADX(config-csw-p1)# match r1 hash-persist url search-url “v4” offset 0
length 3
ServerIronADX(config-csw-p1)# match r2 forward 20
ServerIronADX(config-csw-p1)# match r2 hash-persist url search-host “m1” offset 0
ServerIronADX(config-csw-p1)# match r2 hash-persist url search-host “m2” offset 0