Re: RGW object purging in upstream caches

[Jeff Mitchell <jeffrey.mitchell@gmail.com>]

Wido den Hollander wrote:
> Now, when running just one Varnish instance which does loadbalancing
> over multiple RGW instances is not a real problem. When it sees a PUT
> operation it can "purge" (called banning in Varnish) the object from
> it's cache.
>
> When looking at the scenario where you have multiple caches you run into
> the cache-consistency problem. If an object is modified the caches are
> not notified and will continue to serve an outdated object.
>
> Looking at the Last-Modified header is not an option since the cache
> will not contact RGW when serving out of it's cache.
>
> To handle this there has to be some kind of "hook" inside RGW that can
> notify Varnish (or some other cache) when an object changes.

For nginx, it appears there is a well-tested production module that does 
this: http://labs.frickle.com/nginx_ngx_cache_purge/ (see the examples 
at the end of the README)

--Jeff