JSONP cache busting varnish

[Howard Rauscher]

Using varnish-2.1.5 SVN

On Fri, Apr 29, 2011 at 11:26 AM, Howard Rauscher <howardr at gmail.com> wrote:

> My company had an interactive widget posted on the homepage of a very high
> traffic media company during the Royal Wedding. We were hosting most of the
> widget on Amazon S3, but every 5 seconds we polled our server via JSONP to
> get updated stats about the event.
>
> A couple of weeks ago we realized that JSONP effectively cache busts
> varnish. I searched around the internet and found a novel way to use our
> varnish server to mitigate this situation.
>
> Here is an example of our VCL:
> https://gist.github.com/f1d91b64acdb3f1d7769
>
> At around 5:00am US CST (maybe earlier), about a 1/3 of our api through
> varnish returned 503's. We ended up just removing the relevant JSONP
> solution and let varnish to be cache busted. Now that the situation has
> cooled off a little, I was wondering if I could get some advice on this
> config.
>
> Is this a good solution to the JSONP problem?
>
> Our setup:
>
>    - 6 EC2 servers (not sure which setup)
>    - Each server had one varnish and one webapp
>       - 7188 megs of ram each
>       - 2 GB allocated to varnish
>       - ~1500 req/s
>       - 99.2% hit rate
>       - And example backend success were ~600/s and backend failures were
>       ~300/sec
>
> An example url would be:
> /username/streamname.json?jsonp=callback8&items=item1,item2
>
> The 503 response would contained text "Guru Meditation:XID: 1518618356".
> Not sure what that means though.
>
> thanks,
> Howard
>
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