Re: [squid-users] caching dynamic image content

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.
Received on Thu Aug 13 2009 - 14:32:25 MDT