Documentation on AppEngine's caching reverse proxy

[saidimu apale]

Given the numerous issues (in the issue tracker, GAE mailing-lists and in speculative blog posts in the wild) surrounding cache headers and the GAE reverse proxy, is there definitive documentation on how it handles headers and best-practice interactions?

It is surprising that such an important part of the request-response cycles is rather opaque.

saidimu

[Matt H]

This would be nice to have.

[Ikai Lan (Google)]

App Engine's edge cache is not guaranteed. It's "best effort" caching, caching that any ISP downstream could also have implemented.

What you'd do is set the cache-control headers to "public" and set a max-age, and App Engine's edge caches may cache your content. There's also no way to flush your content, but the cache is key off the URL, so use a cache buster.

--

Ikai Lan 
Developer Programs Engineer, Google App Engine

Blogger: http://googleappengine.blogspot.com

Reddit: http://www.reddit.com/r/appengine

Twitter: http://twitter.com/app_engine

On Fri, Dec 17, 2010 at 9:28 AM, Matt H <matt...@gmail.com> wrote:

This would be nice to have.

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[Mike]

The biggest undocumented features of the edge cache we've had to deal
with is that it does not honor the Vary header, and that it is turned
on when you enable billing for an app.

I agree, however, that regardless of what details are posted in this
group, the edge cache behavior should be documented in the official
docs.

-Mike

-=-

On Dec 17, 9:31 am, "Ikai Lan (Google)" <ikai.l+gro...@google.com>
wrote:

> > google-appengi...@googlegroups.com<google-appengine%2Bunsubscrib e...@googlegroups.com>
> > .

[风笑雪]

Actually, the cache will be refresh after re-deploy.

But I suggest not to set too long max-age for dynamic pages.

Also be noticed that the edge cache is only available for Google Apps domains, no affect on appspot.com.

----------
keakon

My blog(Chinese): www.keakon.net

Blog source code: https://bitbucket.org/keakon/doodle/

[Stephen]

> ... your content, but the cache is key off the URL ...

This is a bug. You should be keying off the URL and the Vary header, or not caching responses with Vary headers:

  http://code.google.com/p/googleappengine/issues/detail?id=4277

This was reported two months ago :-(

[Stephen]

If you haven't already, star this:

  http://code.google.com/p/googleappengine/issues/detail?id=2258


If folks discover new attributes of the cache, by experiment, perhaps they could be added there to collect them in one place.

[saidimu apale]

If folks discover new attributes of the cache, by experiment, perhaps they could be added there to collect them in one place.

Official docs would go a long way in calming the unease of "what other critical attributes haven't been discovered experimentally?" It appears these docs aren't on the agenda at all so I guess it's all experimental for now.

+1 for your idea of collecting them in one place.

saidimu