Re: [squid-users] caching dynamic image content

Terry wrote:
> On Thu, Aug 13, 2009 at 9:32 AM, Terry<td3201_at_gmail.com> wrote:
>> On Thu, Aug 13, 2009 at 8:10 AM, Amos Jeffries<squid3_at_treenet.co.nz> wrote:
>>> Terry wrote:
>>>> Hello,
>>>>
>>>> I don't have squid implemented yet.
>>>>
>>>> I am researching a web architecture issue I am seeing with a site.
>>>> Squid may be a bandaid for what I think may be some poor development
>>>> architecture decisions. There are concerns that the site is written
>>>> in a way that browsers and reverse proxies cannot cache it
>>>> appropriately. And these aren't my concerns by the way. We also have
>>>> A10 load balancers in house that do some caching. They said they
>>>> can't cache this content. I don't want to go into their reasoning
>>>> because I don't believe it.
>>>>
>>>> Here's an example of an image as seen from the client. I pulled this
>>>> right out of my firefox memory cache:
>>>> http://foo.domain.com/Image.aspx?i=db1edbcd-2375-4bae-b33f-a53ced60deed
>>>>
>>>> 1. If it's in the memory cache, can I assume that browsers and proxies
>>>> can cache it? Also, I never saw these objects in my disk cache. Not
>>>> sure if that's significant or not.
>>> No. The browser has additional information such as who is logged in and
>>> whether your session with the website is the same. They are also allowed to
>>> cache objects personal to you.
>>>
>>> Proxies and caches only have the URL and some other limited data to base the
>>> checking on. If there is any chance it was a private object it will not be
>>> cached naturally.
>>>
>>>> 2. Does firefox still interpret this as an image and cache it as one
>>>> or is this considered dynamic content that may be problematic?
>>> Not enough information to even guess. What headers are present? Does the
>>> website require login? does the same image ever change URL (including the
>>> query string) and why/when/how often? are alternative image formats
>>> available at the exact same URL?
>>>
>>> Any one of those answers may make the object non-cacheable by shared
>>> proxies.
>>>
>>>> I think that's enough information to start a conversation. Thanks for
>>>> any insight!
>>> foo.domain.com does not resolve here so I can't verify the object.
>>> Please pick some of the URLs and enter them into http://www.redbot.org for
>>> review of cacheability.
>>>
>>> Amos
>>> --
>>> Please be using
>>> Current Stable Squid 2.7.STABLE6 or 3.0.STABLE18
>>> Current Beta Squid 3.1.0.13
>>>
>>
>> Thank you both for replying. I haven't messed with squid and caching
>> for 5+ years and its all slightly coming back to me. The identifier
>> in the URL is not unique based upon the session of the user.
>> https://foo.domain.com/Image.aspx?i=db1edbcd-2375-4bae-b33f-a53ced60deed
>>
>> the i=db1edbcd-2375-4bae-b33f-a53ced60deed is a unique identifier for
>> the image and its size. Based on that, it should be cacheable but
>> the developers are setting it to nocache for some reason. I am
>> guessing they reused some code for other dynamic content and failed to
>> see this aspect.
>>
>
> Just to further prove its not being cached, here's the header:
>
>
> GET /Pic.aspx?i=db1edbcd-2375-4bae-b33f-a53ced60deed HTTP/1.1
> Host: foo.domain.com
> User-Agent: Mozilla/5.0 (Windows; U; Windows NT 6.1; en-US;
> rv:1.9.1.2) Gecko/20090729 Firefox/3.5.2 (.NET CLR 3.5.30729)
> Accept: image/png,image/*;q=0.8,*/*;q=0.5
> Accept-Language: en-us,en;q=0.5
> Accept-Encoding: gzip,deflate
> Accept-Charset: ISO-8859-1,utf-8;q=0.7,*;q=0.7
> Keep-Alive: 300
> Connection: keep-alive
> Referer: https://foo.domain.com/
> Cookie: com.domain.foo_SessionID=kua4ew454kjodsjpdlojdu55
> Cache-Control: max-age=0

The reply headers are kind of more important for the reply is what gets
stored.

Um, just in case it has not already been done...
  check that the QUERY ACL and its "cache deny" rule are removed from
your squid.conf and "refresh_pattern -i (/cgi-bin/|\?) 0 0% 0" is added
on the line above the dot '.' refresh pattern.

Amos

-- 
Please be using
   Current Stable Squid 2.7.STABLE6 or 3.0.STABLE18
   Current Beta Squid 3.1.0.13