hihi all,
there was another thread talking about load balancing / clustering and
session affinity so now i'm curious to understand more about this.
given the following typical setup:
- one load balancing (dispatcher) server 'in front' of everything and
receives all initial requests (LB)
- multiple app servers (servlet containers) 'behind' (A, B, C, D)
- one database server for all the app servers (DB)
when someone enters a URL in a browser and submits it, this request
goes to the load balance server where it decides which app server to
use for this particular request. but that URL is typically an html
with other embedded resources like .jpg, .css, .js, .gif, and so on.
what really happens?
#1:
the load balancer will go to A for .jpg, go to B for the .css, C for
the .gif, and D for processing the .jsp, and then put it all together
when these 'sub requests' are finished.
#2:
the load balancer chooses one app server, say B, and then B is
responsible for all resource processing required for that URL/request.
my questions are:
is #1 possible?
if #2 happens and henceforth all requests from the same session is
routed to app server B, is this session affinity? (is this aka sticky
sessions?)
is it possible to have #2 happen, and then have subsequent requests
from the same session go to different app servers based on the 'most
available/idle' app server? (is this realistically achievable?...
after each request, the session would need to be copied/updated to all
the other app servers... what happens when this is not done fast enough
before the session's next request?)
woodchuck
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