More proxy work on the httpd trunk
Posted by Jim Jagielski on Friday, July 14. 2006 in ASF
A few days ago I added "hot standby" to the mod_proxy_balancer code in httpd-trunk. This allows for a balancer worker to not be used at all unless all the other workers are unusable (stopped, disabled or in error). Not only does this add useful functionality but it kicked off discussion on other load balance methods (like a cluster set value, kind of like mod_jk's "distance" attribute) as well as how the Proxy module uses the httpd scoreboard.
Apache's scoreboard is a central shared memory structure accessible by all the Apache processes and threads. From the start it's had a very specific function, but it's just so darn useful that there's a real temptation to use it as a central dumping point for all kinds of shared data, which I try to discourage as much as I can. 
So there's discussion now about how to better abstract out the scoreboard, not only to make it easier for modules to "extend" it, without monkeying with it, but also to allow other storage providers to be used. One can see how a memcached-compatible scoreboard would be very useful for load balancing. In essence, I think we're looking at a suite of scoreboards, each for specific purposes, which default to the apr_shm implementation as a baseline. Should be quite useful.
Anyway, I'm looking at other improvements to the proxy balancer, and hope to propose backporting to 2.2.x after sufficient testing and feedback. If you have suggestions or comments, don't hesitate to send them along.
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So there's discussion now about how to better abstract out the scoreboard, not only to make it easier for modules to "extend" it, without monkeying with it, but also to allow other storage providers to be used. One can see how a memcached-compatible scoreboard would be very useful for load balancing. In essence, I think we're looking at a suite of scoreboards, each for specific purposes, which default to the apr_shm implementation as a baseline. Should be quite useful.
Anyway, I'm looking at other improvements to the proxy balancer, and hope to propose backporting to 2.2.x after sufficient testing and feedback. If you have suggestions or comments, don't hesitate to send them along.
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