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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