Forum Discussion
NimbostratusBigIP_DNS VS Capacity Method
Documentation of VS Capacity Method in AskF5 says;
The Virtual Server Capacity load balancing method distributes DNS name resolution requests to pool members (virtual servers) based on a system-generated list of pool members (virtual servers) weighted by capacity. BIG-IP DNS selects the pool member with the greatest capacity most often, but over time, all pool members are returned in responses. When pool members have the same capacity, BIG-IP DNS uses the Round Robin method to select a pool member.
I have a query here. What are all the parameters logically decides the capacity of a pool member/virtual server?
If the project requirement is to distribute DNS based on the_LTM_Active_Pool_MemberCount_per_DC, will it be a good decision to go with VS Capacity Algorithm ? or is there any better algorithm to meet this requirement?
2 Replies
Leonardo_SouzaCirrocumulus
romarIt does not seem to work for me this VS Capacity method, at least in 11.6. In the logs can't see any trace of how a particular VS was selected. Somewhere in a devcentral article saw that "VS Capacity" metric is "how many pool members" for a VS. Here is my test: (1) defined on an LTM 2 VS, one with 4 members, the other with 2 members. The LTM was added to GTM as Big-IP server with "VS discovery" option. Then I have defined on the GTM a pool with the 2 VS from the LTM and made it single member to a Wide IP. The pool was set with preferred "VS Capacity" LB. Defined a listener w/ GSLB enabled. Then I am "dig"-ing the WIP hoping to see only the "4-member" VS. To make sure DNS caching does not get in the way I have set the TTL to 1sec. Tough luck though - I see both VS are more or less randomly selected - it's not a round robin, can get the 4-member VS 3 times in a row then the 2-member 4 times in a row etc - overall is 50%-50%. Enabled debug-level GTM logging - logging to an external syslog server - can't see any trace of the VS choice decision. To add to this - using iqdump can't see any specific VS-level metrics coming from the LTM. Not sure how this is supposed to work w/o GTM polling the LTM for metrics.
