Ryan Murray wrote:
Did you check the timeout on your apache proxy config? Once apache has detected the backend is not available it won't retry again until a certain number of seconds (timeout) has passed. I pretty sure mod_proxy defaults to 60 seconds, which I usually reduce to get a quicker recovery when Tomcat is back up.
I believe indeed that it must be something in that "category".This is a case where precise terminology is helpful, and the usage of words like "caching" is a bit inappropriate, because it tends to orient the thinking toward "browser cache" or "page cache" etc..
I have not verified, but intuitively I would tend to think that no HTTP caching mechanism (browser, server, mod_cache, proxies, etc..) would ever really "cache" error responses, and keep responding the same from some cache memory.
But from some overall performance point of view, it would probably make sense that once a back-end has been detected as being "in error" or "not responding", the front-end server would not just blindly keep flooding it with useless requests.
So, to get back to the original issue : if indeed the observed behaviour derives from such a timeout on the part of mod_proxy, I would suggest to do some thinking about whether it is not better, in a general sense, to leave things as they are, at least if this is a system destined to be deployed in production. After all, I am sure that if the developers of mod_proxy and/or mod_prox_ajp deemed it justified to introduce such a timeout, they probably thought hard about it and decided that it was A Good Thing.
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