Brocade Communications Systems 12.4.00 manual Rehash change in hash weight

Weighted distribution of sites with hash-based persistence 1

The ServerIron ADX sorts the IP addresses for domain www.foo.com in ascending order of the addresses as follows.

1.1.1.42(rank 1)Hash Weight: 1

1.1.1.43(rank 2)Hash Weight: 1

1.1.1.44(rank 3) Hash Weight: 2

The hash table for domain is rehashed using the algorithm described in Section 1.3. The hash table for www.foo.com will be as follows after rehashing.

0	1	2	3
.42	.43	.44	.44

255

.44

The hash-table allocation will be the same after the introduction of a new IP, on all the GSLB controllers with the same set of IPs for the domain. At the same time, this method will provide fair allocation to the newly introduced IP without the need for a protocol between two or more network redundant GSLB controllers. Even if this mechanism is used for two controllers in HA, no hash table synchronization is required between them.

Disabling rehash on introduction of new IP addresses or state change from down to healthy

You can disable rehash on the introduction of a new IP address or change of IP address state from down to healthy. User would typically disable this rehash to avoid breaking the persistence when rehashing is performed. The trade off is the new iP address will not be included in the hash table. User will have to manually rehash at a later time to enable the new IP address to be included.

If the rehashing on state change or introduction of a new IP is disabled, and such an event occurs, then a message stating that the ServerIron ADX needs to be rehashed at a later time will be displayed.

Rehash: change in hash weight

ServerIron ADX will rehash the hash table for a domain when the hash weight for an IP configured for the domain is changed. The rehashing will be similar to that described in Section 1.4.

Disabling rehash on change in hash weight configuration

You can disable rehash on change in hash weight configuration for domain IP addresses. User would typically disable this rehash to avoid breaking the persistence when rehashing is performed due to change in hash weight. The trade-off is the new weight for the IP address will not be reflected in the hash bucket assignments for the hash table. User will have to manually rehash at a later convenient time to enable the new weight to be used in hash table assignments.

Configuring distribution of sites with hash-based persistence

With the weighted hash-based GSLB persistence, users will be able to define hash weights for IPs for a domain. The hash buckets will be distributed among the domain IP addresses in proportion to these weights.

The new command line interface needed for weighted hash-based GSLB persistence is described below.

ServerIron ADX Global Server Load Balancing Guide	79
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