Hi all.
This is just a question out of curiousity. Is there a balancer solution that
can allow for controlled migration/upgrade of nodes?
To explain, suppose you have Apache/mod_jk and you have N Tomcats in balance
over that setup, same web application on all of them. Now, suppose you would
like to upgrade the application without disrupting the service. Suppose you
have fixed a bug.
It would be nice if one of the nodes in "cluster" could be brought out of the
cluster, but gracefully. By "gracefully" I refer to stopping new requests to
the node and letting existing requests "drain out". When all requests are over,
it can be brought down and upgraded. Then it would obviously need to be brought
back in. Let us suppose that the new web application is not in "semantical
inbalanace" with the old nodes.
Of course, this brings into question what is "draining out existing requests"?
Does that mean open HTTP sessions or just rrunning requests. I suppose, in case
of session, we could turn to sticky sessions, right?
So, what are your thoughts on the subject? Ever seen something like that in the
wild? Or at least in the lab? A balancer that can be reconfigured (almost)
online and one that allows for requests to the node being evicted to finish,
first.
Nix.
