> What I need is a cache of data that is aware that the validity of its data is
> dependent on who - foo or bar - is retrieving it. In practice, this means that
> requests from both foo and bar may be responded to with cache data from
> the other's previous request, but most likely the cache will be populated with
> responses to foo's requests to the benefit of bar, which is fine.
>
> I too get charged for hitting /myhost.io/go when my clients hit /foo and /bar.
>
> It would be great if I could config my way into a solution to my use-case
> using NGINX.

Just a quick idea (though maybe there is a more elegant way).

Depending on how do you charge your clients (like if it matters which client actually made the request to the origin) instead of using the same proxy_cache for both you could make 2 separate caches (one for the 5 min other for 10 min) and then chain them.

Something like:

location /foo {
proxy_pass "http://myhost.io/go";
proxy_cache 5min_shared_cache;
proxy_cache_valid any 5m;
}

location /bar {
proxy_pass http://localhost/foo; // obviously you need to adjust/rewrite the uris
proxy_cache 10min_shared_cache;
proxy_cache_valid any 10m;
}

So in case there is a request to /foo it will be forwarded to origin and cached for 5 mins,
if there is request to /bar - a subrequest will be made to /foo and if there is a cached object in the 5min cache you'll get the object without making request to origin and the object will be saved for 10 mins, but if there is no object in the 5 min cache a single request to origin will populate both caches.


There are some drawbacks of course - the /bar requests will always populate also the 5min /foo cache - so every object will be saved twice = extra disk space.

Also depending if you ignore or not the Expires (origin) headers the object in the 10min cache could end up actually older than 10 minutes (if you get the object from the 5min cache at 4:59 age (sadly nginx doesn't have Age header) and then add 10 mins to it. So it may or may not be a problem if you can adjust the times a bit - like add only ~7 minutes if the /foo responds with cache hit status)

Going the other way around (/foo -> /bar) could be possible but has extra complexity (like checking if the object is not too old etc) for example using LUA you could implement whole proxy and file store logic.

rr




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