Hash-based slb with server persistence, Persistent hash table – Brocade Virtual ADX Server Load Balancing Guide (Supporting ADX v03.1.00) User Manual
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Brocade Virtual ADX Server Load Balancing Guide
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Hash-based SLB with server persistence
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The time remaining for the holddown state is displayed by the show server real detail command as
shown in the following.
Hash-based SLB with server persistence
This feature provides a persistent hashing mechanism for virtual server ports, which evenly
distributes hash assignments and enables a client to always be redirected to the same real server.
Command support is also provided to help you manage the introduction of a new server.
This feature enables a client to always be redirected to the same real server. The client will be
directed to a new real server only if the assigned real server fails.
By default, SLB uses stateful load balancing for Virtual IP addresses (VIPs). In stateful load
balancing, the Brocade Virtual ADX creates session table entries for the connections between the
client and the destination (the real server). If multiple real servers are bound to a VIP, then
requests from the same client can be serviced by different real servers over a period of time.
However, for transaction-oriented systems, a client might need to be serviced by the same real
server each time the client makes a request, regardless of the length of time between each request
made.
Using the sticky feature, the current maximum persistence possible for Stateful SLB is 20 hours.
This setting might not be sufficient for systems that always need the client to be directed to the
same real server, unless an event such as real server failure necessitates reassignment of the
client to a different server.
Persistent hash table
Each virtual server port maintains a persistent hash table consisting of 256 entries. When the
Brocade Virtual ADX boots up, all the hash entries in the table are empty (no real server
assignments to any of the entries). When a client makes a request to the VIP, the Brocade Virtual
ADX calculates a hash value based on the client IP. The hash will be a value between 0 and 255
and will map to one of the entries in the persistent hash table. The Brocade Virtual ADX then
retrieves the persistent hash table entry for the calculated hash value. If there is no real server
allocated for the table entry, the Brocade Virtual ADX selects a real server for that table entry using
the configured SLB predictor. The system will then assign the real server to the table entry, and the
client request will be serviced by the real server.
Virtual ADX(config)#show server real rs1 det
http HLD 0 0 0 0 0 0 0 0
max_conn = 10 fail time = 0, Vir IP 192.168.1.2
tcp conn rate:udp conn rate = 0:0, max tcp conn rate:max udp conn rate =
0:0
BP max local conn configured No: 0 0 0 0 0 0
BP max conn percentage configured No: 0 0 0 0 0 0
Use local conn : No
resp_time = 7
Keepalive(G/L:Off/On):On
Status Code(s): default (200-299, 401)
HTTP URL: "HEAD /"
tcp-age: 30
Hold-down time remaining: 25 second(s)
dns ACT 0 0 39 39 45 10151 3972 0