A 503 page gets written to my proxy cache, overwriting the 200

Hi,

I’m trying to use the proxy cache to store regular pages (200) from my
web
server so that when the web server goes into maintenance mode and starts
returning 503 nginx can still serve the good page out of cache. It
works
great for a few minutes but then at some point (5 to 10 minutes in)
nginx
will overwrite the good 200 page in the cache with the bad 503 page and
then
start handing out the 503. Looking at my config I don’t understand how
a
503 could ever get written to cache but it is. And the 200 page was
brand
new (written 10 minutes before) so it shouldn’t be the “inactive” time
on
the proxy_cache_path setting causing nginx to delete the good file. Can
anyone tell me what I’m missing? Here are the relevant pieces of my
config:

    proxy_cache_path  /var/www/cache levels=1:2 

keys_zone=my-cache:500m
max_size=3000m inactive=120h;
proxy_temp_path /var/www/cache/tmp;
proxy_cache_key “$scheme$host$request_uri”;

    map $http_cookie $GotSessionCookie {
            default "";
            "~(?P<sessionid>\bSESS[^;=]+=[^;=]+)" $sessionid;
    }

    server {
            listen 80;
            server_name _;

            proxy_cache my-cache;

            location / {
                    proxy_pass http://production;
                    proxy_cache_valid  200 301 302  30m;
                    proxy_cache_valid  404 1m;
            }

            # don't cache pages with php's session cookie
            proxy_no_cache $cookie_$GotSessionCookie;

            # bypass the cache if we get a X-NoCache header
            proxy_cache_bypass $http_nocache 

$cookie_$GotSessionCookie;

            proxy_cache_use_stale http_500 http_503 error timeout

invalid_header updating;
}

I can’t imagine how a 503 would ever get cached given those
proxy_cache_valid lines but maybe I don’t understand something. Thanks
for
any ideas!

-Rick

Posted at Nginx Forum:
http://forum.nginx.org/read.php?2,246507,246507#msg-246507

Hello!

On Thu, Jan 16, 2014 at 09:02:36AM -0500, rge3 wrote:

the proxy_cache_path setting causing nginx to delete the good file. Can
anyone tell me what I’m missing? Here are the relevant pieces of my
config:

[…]

I can’t imagine how a 503 would ever get cached given those
proxy_cache_valid lines but maybe I don’t understand something. Thanks for
any ideas!

An exiting cache can be bypassed due to proxy_cache_bypass in your
config, and 503 response can be cached if it contains
Cache-Control and/or Expires which allow caching.


Maxim D.
http://nginx.org/

Maxim D. Wrote:

An exiting cache can be bypassed due to proxy_cache_bypass in your
config, and 503 response can be cached if it contains
Cache-Control and/or Expires which allow caching.

Oh, I hadn’t thought of that part about the bypass. Okay, that makes
sense.
But what about the Cache-Control/Expires causing it to cache the 503…
that can
still happen even if my “proxy_cache_valid” line doesn’t list a 503?

-Rick

Posted at Nginx Forum:
http://forum.nginx.org/read.php?2,246507,246517#msg-246517

Maxim D. Wrote:

The “proxy_cache_valid” directives are used if there are no
Cache-Control/Expires to allow caching (or they are ignored with
proxy_ignore_headers). That is, with “proxy_cache_valid” you can
cache something which isn’t normally cached, but they don’t
prevent caching of other responses.

That was my missing piece. Thanks so much!! Now it makes sense!

-R

Posted at Nginx Forum:
http://forum.nginx.org/read.php?2,246507,246558#msg-246558

Hello!

On Thu, Jan 16, 2014 at 02:50:41PM -0500, rge3 wrote:

that can
still happen even if my “proxy_cache_valid” line doesn’t list a 503?

The “proxy_cache_valid” directives are used if there are no
Cache-Control/Expires to allow caching (or they are ignored with
proxy_ignore_headers). That is, with “proxy_cache_valid” you can
cache something which isn’t normally cached, but they don’t
prevent caching of other responses.


Maxim D.
http://nginx.org/

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