[squid-users] stale-if-error returning a 502
Alex Rousskov
rousskov at measurement-factory.com
Fri Feb 9 14:31:08 UTC 2024
On 2024-02-09 08:53, Robin Carlisle wrote:
> I am trying the config workaround approach.
Please keep us posted on your progress.
> Below is the config snippet I have added. I made the
> assumption that for the /refresh_pattern, max-stale=NN /config, the NN
> is in minutes as per the rest of that config directive.
That assumption is natural but incorrect: Unlike the anonymous
positional min and max parameters (that use minutes), refresh_pattern
max-stale=NN uses seconds. Documentation improvements are welcome.
Said that, the workaround should still prevent the application of the
broken default refresh_pattern max-stale=0 rule, so you should still see
positive results for the first NN seconds of the response age.
Instead of specifying max-stale=NN, consider adding refresh_pattern
rules recommended by squid.conf.documented (and included in
squid.cond.default). Those rules do not have max-stale options at all,
and, hence, Squid will use (explicit or default) max_stale directive
instead.
HTH,
Alex.
> I am testing this right now
>
> # this should allow stale objects up to 1 year if allowed by
> Cache-Control repsonseheaders ...
>
> # ... setting both options just in case
>
> max_stale 525600 minutes
>
> refresh_pattern . 0 20% 4320 max-stale=525600
>
>
> Thanks again for your help
>
>
> Robin
>
>
>
>
> On Thu, 8 Feb 2024 at 17:42, Alex Rousskov
> <rousskov at measurement-factory.com
> <mailto:rousskov at measurement-factory.com>> wrote:
>
> Hi Robin,
>
> AFAICT from the logs you have privately shared and your
> squid.conf
> that you have posted earlier, your Squid overwrites
> stale-if-error=31536000 in the response with "refresh_pattern
> max-stale=0" default. That 0 value is wrong. The correct value
> should be
> taken from max_stale directive that defaults to 1 week, not zero:
>
> refresh_pattern
> ...
> max-stale=NN provide a maximum staleness factor. Squid won't
> serve objects more stale than this even if it failed to
> validate the object. Default: use the max_stale global limit.
>
> This wrong default is a Squid bug AFAICT. I posted an _untested_ fix as
> Squid PR 1664: https://github.com/squid-cache/squid/pull/1664
> <https://github.com/squid-cache/squid/pull/1664>
>
> If possible, please test the corresponding patch:
> https://github.com/squid-cache/squid/commit/571973589b5a46d458311f8b60dcb83032fd5cec.patch <https://github.com/squid-cache/squid/commit/571973589b5a46d458311f8b60dcb83032fd5cec.patch>
>
> AFAICT, you can also work around that bug by configuring an explicit
> refresh_pattern rule with an explicit max-stale option (see
> squid.conf.documented for examples). I have not tested that theory
> either.
>
>
> HTH,
>
> Alex.
>
>
> On 2024-02-07 13:45, Robin Carlisle wrote:
> > Hi,
> >
> > I have just started my enhanced logging journey and have a small
> snippet
> > below that might illuminate the issue ...
> >
> > /2024/02/07 17:06:39.212 kid1| 88,3| client_side_reply.cc(507)
> > handleIMSReply: origin replied with error 502, forwarding to
> client due
> > to fail_on_validation_err/
> >
> > A few lines below in the log it looks like squid sent :-
> >
> > /2024/02/07 17:06:39.212 kid1| 11,2| Stream.cc(280)
> sendStartOfMessage:
> > HTTP Client REPLY:
> > ---------
> > HTTP/1.1 502 Bad Gateway
> > Server: squid/5.7
> > Mime-Version: 1.0
> > Date: Wed, 07 Feb 2024 17:06:39 GMT
> > Content-Type: text/html;charset=utf-8
> > Content-Length: 3853
> > X-Squid-Error: ERR_READ_ERROR 0
> > Vary: Accept-Language
> > Content-Language: en
> > X-Cache: MISS from labs-maul-st-15
> > X-Cache-Lookup: HIT from labs-maul-st-15:3129
> > Via: 1.1 labs-maul-st-15 (squid/5.7)
> > Connection: close/
> >
> >
> > The rest of the logs are quite large and contain URLs I cannot put
> > here. The logs were generated with debug_options to ALL,3.
> >
> > Any ideas? Or should I generate more detailed logs and send them
> > privately?
> >
> > Thanks again,
> >
> > Robin
> >
> >
> >
> >
> > On Fri, 2 Feb 2024 at 11:20, Robin Carlisle
> > <robin.carlisle at framestore.com
> <mailto:robin.carlisle at framestore.com>
> <mailto:robin.carlisle at framestore.com
> <mailto:robin.carlisle at framestore.com>>>
> > wrote:
> >
> > Hi, thanks for your reply.
> >
> > I have been looking at :
> >
> https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Cache-Control <https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Cache-Control> <https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Cache-Control <https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Cache-Control>>
> >
> > /The stale-if-error response directive indicates that the
> cache can
> > reuse a stale response when an upstream server generates an
> error,
> > or when the error is generated locally. Here, an error is
> considered
> > any response with a status code of 500, 502, 503, or 504.
> >
> > Cache-Control: max-age=604800, stale-if-error=86400
> > In the example above, the response is fresh for 7 days (604800s).
> > Afterwards, it becomes stale, but can be used for an extra 1 day
> > (86400s) when an error is encountered.
> >
> > After the stale-if-error period passes, the client will
> receive any
> > error generated/
> >
> > Given what you have said and what the above docs say - I am still
> > confused as it looks like (in my test cases) the cached
> response can
> > be used for 3600 secs (this works), after which the cached
> response
> > can still be used for an additional 31536000 seconds on an error
> > (this doesnt work).
> >
> > I am going to dig into the error logging you suggested to see
> if I
> > can make sense of that - and will send on if I can't.
> >
> > Thanks v much for your help again,
> >
> > Robin
> >
> >
> >
> >
> >
> > On Thu, 1 Feb 2024 at 18:27, Alex Rousskov
> > <rousskov at measurement-factory.com
> <mailto:rousskov at measurement-factory.com>
> > <mailto:rousskov at measurement-factory.com
> <mailto:rousskov at measurement-factory.com>>> wrote:
> >
> > On 2024-02-01 12:03, Robin Carlisle wrote:
> > > Hi, I am having trouble with stale-if-error response.
> >
> > If I am interpreting Squid code correctly, in primary use
> cases:
> >
> > * without a Cache-Control:stale-if-error=X in the original
> > response,
> > Squid sends a stale object if revalidation results in a
> 5xx error;
> >
> > * with a Cache-Control:stale-if-error=X and object age at
> most
> > X, Squid
> > sends a stale object if revalidation results in a 5xx error;
> >
> > * with a Cache-Control:stale-if-error=X and object age
> exceeding X,
> > Squid forwards the 5xx error response if revalidation
> results in
> > a 5xx
> > error;
> >
> > In other words, stale-if-error=X turns on a "fail on
> validation
> > errors"
> > behavior for stale objects older than X. It has no other
> effects.
> >
> > In your test case, the stale objects are much younger than
> > stale-if-error value (e.g., Age~=3601 vs.
> stale-if-error=31536000).
> > Thus, stale-if-error should have no relevant effect.
> >
> > Something else is probably preventing your Squid from serving
> > the stale
> > response when facing a 5xx error. I do not know what that
> > something is.
> >
> > I recommend sharing (privately if you need to protect
> sensitive
> > info) a
> > pointer to a compressed ALL,9 cache.log collected while
> > reproducing the
> > problem (using two transactions similar to the ones you
> have shared
> > below -- a successful stale hit and a problematic one):
> >
> https://wiki.squid-cache.org/SquidFaq/BugReporting#debugging-a-single-transaction <https://wiki.squid-cache.org/SquidFaq/BugReporting#debugging-a-single-transaction> <https://wiki.squid-cache.org/SquidFaq/BugReporting#debugging-a-single-transaction <https://wiki.squid-cache.org/SquidFaq/BugReporting#debugging-a-single-transaction>>
> >
> > Alternatively, you can try to study cache.log yourself after
> > setting
> > debug_options to ALL,3. Searching for "refresh" and
> > "handleIMSReply" may
> > yield enough clues.
> >
> >
> > HTH,
> >
> > Alex.
> >
> >
> >
> >
> > > # /etc/squid/squid.conf :
> > >
> > > acl to_aws dstdomain .amazonaws.com
> <http://amazonaws.com> <http://amazonaws.com <http://amazonaws.com>>
> > <http://amazonaws.com <http://amazonaws.com>
> <http://amazonaws.com <http://amazonaws.com>>>
> > >
> > > acl from_local src localhost
> > >
> > > http_access allow to_aws
> > >
> > > http_access allow from_local
> > >
> > > cache allow all
> > >
> > > cache_dir ufs /var/cache/squid 1024 16 256
> > >
> > > http_port 3129 ssl-bump cert=/etc/squid/maul.pem
> > > generate-host-certificates=on
> dynamic_cert_mem_cache_size=4MB
> > >
> > > sslcrtd_program /usr/lib/squid/security_file_certgen -s
> > > /var/lib/squid/ssl_db -M 4MB
> > >
> > > acl step1 at_step SslBump1
> > >
> > > ssl_bump bump step1
> > >
> > > ssl_bump bump all
> > >
> > > sslproxy_cert_error deny all
> > >
> > > cache_store_log stdio:/var/log/squid/store.log
> > >
> > > logfile_rotate 0
> > >
> > > shutdown_lifetime 3 seconds
> > >
> > >
> > > # /usr/bin/proxy-test :
> > >
> > > #!/bin/bash
> > >
> > > curl --proxy http://localhost:3129
> <http://localhost:3129> <http://localhost:3129 <http://localhost:3129>>
> > <http://localhost:3129 <http://localhost:3129>
> <http://localhost:3129 <http://localhost:3129>>> \
> > >
> > > --cacert /etc/squid/stuff.pem \
> > >
> > > -v
> "https://stuff.amazonaws.com/api/v1/stuff/stuff.json
> <https://stuff.amazonaws.com/api/v1/stuff/stuff.json>
> > <https://stuff.amazonaws.com/api/v1/stuff/stuff.json
> <https://stuff.amazonaws.com/api/v1/stuff/stuff.json>>
> > > <https://stuff.amazonaws.com/api/v1/stuff/stuff.json
> <https://stuff.amazonaws.com/api/v1/stuff/stuff.json>
> > <https://stuff.amazonaws.com/api/v1/stuff/stuff.json
> <https://stuff.amazonaws.com/api/v1/stuff/stuff.json>>>" \
> > >
> > > -H "Authorization: token MYTOKEN" \
> > >
> > > -H "Content-Type: application/json" \
> > >
> > > --output "/tmp/stuff.json"
> > >
> > >
> > >
> > > Tests ..........
> > >
> > >
> > > At this point in time the network cable is
> unattached. Squid
> > returns
> > > the cached object it got when the network was online
> earlier.
> > The Age of
> > > this object is just still under the max_age of 3600.
> > Previously I
> > > was using offline_mode but I found that it did not try to
> > revalidate
> > > from the origin after the object expired (defined via
> max-age
> > response).
> > > My understanding is that stale-if-error should work
> under my
> > > circumstances.
> > >
> > >
> > > # /var/log/squid/access.log
> > >
> > > 1706799404.440 6 127.0.0.1 NONE_NONE/200 0 CONNECT
> > > stuff.amazonaws.com:443
> <http://stuff.amazonaws.com:443> <http://stuff.amazonaws.com:443
> <http://stuff.amazonaws.com:443>>
> > <http://stuff.amazonaws.com:443
> <http://stuff.amazonaws.com:443>
> > <http://stuff.amazonaws.com:443
> <http://stuff.amazonaws.com:443>>> - HIER_NONE/- -
> > >
> > > 1706799404.440 0 127.0.0.1 TCP_MEM_HIT/200 20726 GET
> > > https://stuff.amazonaws.com/stuff.json
> <https://stuff.amazonaws.com/stuff.json>
> > <https://stuff.amazonaws.com/stuff.json
> <https://stuff.amazonaws.com/stuff.json>>
> > > <https://stuff.amazonaws.com/stuff.json
> <https://stuff.amazonaws.com/stuff.json>
> > <https://stuff.amazonaws.com/stuff.json
> <https://stuff.amazonaws.com/stuff.json>>> - HIER_NONE/-
> > application/json
> > >
> > >
> > > # extract from /usr/bin/proxy-test
> > >
> > > < HTTP/1.1 200 OK
> > >
> > > < Date: Thu, 01 Feb 2024 13:57:11 GMT
> > >
> > > < Content-Type: application/json
> > >
> > > < Content-Length: 20134
> > >
> > > < x-amzn-RequestId: 3a2d3b26-df73-4b30-88cb-1a9268fa0df2
> > >
> > > < Last-Modified: 2024-02-01T13:00:45.000Z
> > >
> > > < Access-Control-Allow-Origin: *
> > >
> > > < x-amz-apigw-id: SdZwpG7qiYcERUQ=
> > >
> > > < Cache-Control: public, max-age=3600,
> stale-if-error=31536000
> > >
> > > < ETag: "cec102b43372840737ab773c2e77858b"
> > >
> > > < X-Amzn-Trace-Id:
> Root=1-65bba337-292be751134161b03555cdd6
> > >
> > > < Age: 3573
> > >
> > > < X-Cache: HIT from labs-maul-st-31
> > >
> > > < X-Cache-Lookup: HIT from labs-maul-st-31:3129
> > >
> > > < Via: 1.1 labs-maul-st-31 (squid/5.7)
> > >
> > > < Connection: keep-alive
> > >
> > >
> > >
> > >
> > > Below .. the curl script executes again. The Age has gone
> > over the
> > > max-age so squid attempted to refresh from the
> origin. The
> > machine is
> > > still offline so the refresh failed. I expected that the
> > > stale-if-error response would instruct squid to return the
> > cached object
> > > as a 200.
> > >
> > >
> > > # /var/log/squid/access.log
> > >
> > > 1706799434.464 5 127.0.0.1 NONE_NONE/200 0 CONNECT
> > > stuff.amazonaws.com:443
> <http://stuff.amazonaws.com:443> <http://stuff.amazonaws.com:443
> <http://stuff.amazonaws.com:443>>
> > <http://stuff.amazonaws.com:443
> <http://stuff.amazonaws.com:443>
> > <http://stuff.amazonaws.com:443
> <http://stuff.amazonaws.com:443>>> - HIER_NONE/- -
> > >
> > > 1706799434.464 0 127.0.0.1
> TCP_REFRESH_FAIL_ERR/502 4235
> > GET
> > > https://stuff.amazonaws.com/stuff.json
> <https://stuff.amazonaws.com/stuff.json>
> > <https://stuff.amazonaws.com/stuff.json
> <https://stuff.amazonaws.com/stuff.json>>
> > > <https://stuff.amazonaws.com/stuff.json
> <https://stuff.amazonaws.com/stuff.json>
> > <https://stuff.amazonaws.com/stuff.json
> <https://stuff.amazonaws.com/stuff.json>>> - HIER_NONE/- text/html
> > >
> > >
> > > # extract from /usr/bin/proxy-test
> > >
> > > < HTTP/1.1 502 Bad Gateway
> > >
> > > < Server: squid/5.7
> > >
> > > < Mime-Version: 1.0
> > >
> > > < Date: Thu, 01 Feb 2024 14:57:14 GMT
> > >
> > > < Content-Type: text/html;charset=utf-8
> > >
> > > < Content-Length: 3853
> > >
> > > < X-Squid-Error: ERR_READ_ERROR 0
> > >
> > > < Vary: Accept-Language
> > >
> > > < Content-Language: en
> > >
> > > < X-Cache: MISS from labs-maul-st-31
> > >
> > > < X-Cache-Lookup: HIT from labs-maul-st-31:3129
> > >
> > > < Via: 1.1 labs-maul-st-31 (squid/5.7)
> > >
> > > < Connection: close
> > >
> > >
> > >
> > > Hope someone can help me with this. All the best,
> > >
> > >
> > > Robin Carlisle
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