i personally restrict caching to static files with headers from the backend because they are a lot of (images, javscript, css) and never cache any dynamic page itself
even in this case ATS gives a performance boost and you can handle a lot of more clients while stay at httpd-prefork at the backend for a lot of reasons (connection isolation, stability...) Am 17.04.2014 21:58, schrieb Bacon Tuna: > I'm actually not concerned about the backend availability as I am about the > gateways. If the gateways die nothing > works. Here's a little more info in a scenario format: > > Client requests object from ATS. > Request is handled by geographic load balancer and directed to a cluster in > once data center 'A'. > The cluster fetches the object and caches it. > Client makes request for object again. > Request is handled by geo load balancer and directed to cluster in data > center 'B'. > Client requests object purged from cache. > Purge request is handled by geo load balancer and directed to cluster in data > center 'A' > Cluster invalidates object. > > At this point the cache across 'A' and 'B' is inconsistent. Further requests > would either retrieve a "stale" object > or fetch a new object and cache it. Both objects would persist. > > Do folks just preach "eventual consistency", or handle this via some other > means? > > > > > On Thu, Apr 17, 2014 at 11:48 AM, Reindl Harald <[email protected] > <mailto:[email protected]>> wrote: > > > > Am 17.04.2014 20:41, schrieb Bacon Tuna: > > I haven't had luck finding white papers or documentation discussing > strategies for running ATS clusters across > > multiple data centers or availability zones to support high > availability? > > > > Any chance someone on here can point me in the right direction? > > > > Do people load balance multiple clusters with separate caches, or do > they employ some mechanism to maintain > > consistency across regions? > > i would let caches alone, it get's filled alone and has no imprtant data > > if you only have one backend and some ATS for load-balancing you are > completly fine - your spread your load and take a lot of away from > the backend server possible resulting in you have no need for more > backend servers - the high ability itself of the backend can by > something like VMware HA or whatever doing failover > > if you need more than one backendserver you should take much > more care to keep sessions between the backends synchronous > to avoid troubles having one request of the same client on > two different backend servers and log the client out
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