Solution to CS526 S2006 Homework #3

Solution to Homework #3: Configure LVS using VMware Virtual Machines and Secure Web Access and Client Digital Certificates

Description:

Part1 . LVS configuration.

Question A: In what cases wlc perform better than wrr? Describe a simple case that highlights that.
Ans: When the job sizes are uneven, the wrr will distribute new requests to real servers already overloaded with previous long servicing requests. WLC on the other hand will check how many activeconnection and assign the new requests to the real server with fewer active connctions.

Assume that there are two type of jobs. Job A takes base real server one hour to complete while job B takes one minute to complete. The jobs repeatedly arrive at the beginning 3 min interval with the pattern of type A, type A, type B. Assume that we have three real servers with weights of 2, 1, and 1, where the first real server is twice as fast as the rest of base real server. With the arrival pattern, after the first three job arrives, we have the following table how the remaing task in term of minutes to be performed by the job(s) allocated to the real servers.

With WRR

Time	Server1	Server2	Server3
0	job1(TA;60min)	job2(TA;60min)	job3(TB;1min)
1min	job1(TA;58min)	job2(TA;59min)	--idle
3min	job1(TA;54min) job4(TA;60min)	job2(TA;57min) job5(TA;60min)	job6(TB,1min)
4min	job1(TA;53min) job4(TA;59min)	job2(TA;56.5min) job5(TA;59.5min)	--idle
6min	job1(TA;51min) job4(TA;57min) job7(TA;60min)	job2(TA;55.5min) job5(TA;58.5min) job8(TA;60min)	job9(TB;1min)

With WLC

Time	Server1	Server2	Server3
0	job1(TA;60min)	job2(TA;60min)	job3(TB;1min)
1min	job1(TA;58min)	job2(TA;59min)	--idle
3min	job1(TA;54bin) job5(TA;60min)	job2(TA;57min) job6(TB;1min)	job4(TA;60min)
4min	job1(TA;53min) job5(TA;59min)	job2(TA;56.5min) job6(TB;0.5min)	job4(TA;59min)
6min	job1(TA;51min) job5(TA;57min) job7(TA;60min)	job2(TA;55min) job8(TA;60min)	job4(TA;57min) job9(TB;1min)