1 Weighted distribution of sites with
In our example,
Hash bucket 0 will be assigned to 1.1.1.42
Hash bucket 1 will be assigned to 1.1.1.43
Hash bucket 2 will be assigned to 1.1.1.44
Hash bucket 3 will be assigned to 1.1.1.44
Hash bucket 4 will be assigned to 1.1.1.42
Hash bucket 5 will be assigned to 1.1.1.43
Hash bucket 6 will be assigned to 1.1.1.44
Hash bucket 7 will be assigned to 1.1.1.44
And so on.
In other words, for every bucket assigned to 1.1.1.42, one will be assigned to 1.1.1.43 and two will be assigned to 1.1.1.44 i.e. assignments will be done in a round robin manner in proportion to the hash weights.
The hash table for www.foo.com will be as follows.
0 | 1 | 2 | 3 |
.42 | .43 | .44 | .44 |
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255
.44
If the IP address of a client querying for www.foo.com hashes to hash index 2, then 1.1.1.44 will be selected as the best IP address for this client.
IP address failure or removal from domain
In the previous example, assume user removes 1.1.1.44 for domain www.foo.com. The IP addresses remaining for www.foo.com are as follows.
1.1.1.42(rank 1)Hash weight 1
1.1.1.43(rank 2)Hash weight 1
In this scenario, all the hash indexes allocated to 1.1.1.44 will be reassigned to 1.1.1.42 and 1.1.1.43 in proportion to their weights.
The basic algorithm used will be same as that described in section 1.3. The difference is that only buckets that have been assigned to 1.1.1.44 will be reassigned.
Rehashing for new IP address for a domain or state change from down to up
This section describes how the ServerIron ADX handles the introduction of a new IP address for a domain or change of state of an IP address from down to healthy.
For example, following IP addresses are configured for www.foo.com.
1.1.1.42(rank 1)Hash Weight: 1
1.1.1.43(rank 2) Hash Weight: 1
The hash table allocation looks like the following:
0 | 1 | 2 | 3 |
.42 .43 .42 .43
Now the new IP address 1.1.1.44 is configured for domain www.foo.com.
255
.43
78 | ServerIron ADX Global Server Load Balancing Guide |
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