Technical data

90 ServerIron ADX Advanced Server Load Balancing Guide
53-1002435-03
Traffic distribution based on cache server capacity
2
1. ServerIron ADX sends periodic SNMP queries to the cache server.
2. ServerIron ADX sets the cache server state based on the reply it receives from the cache
server.
3. For an incoming connection, a hash is computed based on its load state.
* In order to delete the existing connection on an offline/initializing cache server immediately the
server force-delete command needs to be configured.
** Overflow connections indicates that the connection that previously hashed to a cache server
that is currently either burdened, stressed, overloaded, overtaxed, halting or offline.
*
TABLE 10 Hash allocation and load balancing performed by ServerIron ADX doing Layer-4 TCS based on the
load state of the cache server
Cache server
state
Allocated hash
bucket
New connections Overflow
connections**
Existing
connections
Clears hash
buckets
Underused Yes Allows Allows Allows No
Normal Yes Allows Allows Allows No
Burdened Yes Allows Allows Allows No
Stressed Yes Allows (If no other
cache is
available)
Does not allow Allows No
Overloaded/
overtaxed
Yes Does not allow Does not allow Allows No
Halting No Does not allow Does not allow Allows Yes
Offline No Does not allow Does not allow Deletes* Yes
Initializing Yes Does not allow Does not allow Deletes* No
TABLE 11 Transaction allocation and load balancing performed by ServerIron ADX doing Layer-7 TCS based on
the load state of the cache server
Cache Server state New transactions Existing transactions
Underused Allows Allows
Normal Allows Allows
Burdened Allows Allows
Stressed Allows (If no other cache in SNMP state 1 to 3 exists. Otherwise, all
the transactions will go to caches whose state is in between 1 to 3.
Allows
Overloaded/
overtaxed
Does not allow Allows
Halting Does not allow Allows
Offline Does not allow Allows
Initializing Does not allow Allows