Best way to cache RESTful API results of GET calls
I'm thinking about the best way to create a cache layer in front or as first layer for GET requests to my RESTful API (written in Ruby).
Not every request can be cached, because even for some GET requests the API has to validate the requesting user / application. That means I need to configure which request is cacheable and how long each cached answer is valid. For a few cases I need a very short expiration time of eg 15s and below. And I should be able to let cache entries expire by the API application even if the expiration date is not reached yet.
I already thought about many possible solutions, my two best ideas:
first layer of the API (even before the routing), cache logic by myself (to have all configuration options in my hand), answers and expiration date stored to Memcached
a webserver proxy (high configurable), perhaps something like Squid but I never used a proxy for a case like this before and I'm absolutely not sure about it
I also thought about a cache solution like Varnish, I used Varnish for "usual" web applications and it's impressive but the configuration is kind of special. But I would use it if it's the fastest solution.
An other thought was to cache to the Solr Index, which I'm already using in the data layer to not query the database for most requests.
If someone has a hint or good sources to read about this topic, let me know.
memcached is a great option, and I see you mentioned this already as a possible option. Also Redis seems to be praised a lot as another option at this level.
On an application level, in terms of a more granular approach to cache on a file by file and/or module basis, local storage is always an option for common objects a user may request over and over again, even as simple as just dropping response objects into session so that can be reused vs making another http rest call and coding appropriately.
Now people go back and forth debating about varnish vs squid, and both seem to have their pros and cons, so I can't comment on which one is better but many people say Varnish with a tuned apache server is great for dynamic websites.
Firstly, build your RESTful API to be RESTful. That means authenticated users can also get cached content as to keep all state in the URL it needs to contain the auth details. Of course the hit rate will be lower here, but it is cacheable.
With a good deal of logged in users it will be very beneficial to have some sort of model cache behind a full page cache as many models are still shared even if some aren't (in a good OOP structure).
Then for a full page cache you are best of to keep all the requests off the web server and especially away from the dynamic processing in the next step (in your case Ruby). The fastest way to cache full pages from a normal web server is always a caching proxy in front of the web servers.
Varnish is in my opinion as good and easy as it gets, but some prefer Squid indeed.
Since REST is an HTTP thing, it could be that the best way of caching requests is to use HTTP caching.
Look into using ETags on your responses, checking the ETag in requests to reply with '304 Not Modified' and having Rack::Cache to serve cached data if the ETags are the same. This works great for cache-control 'public' content.
Rack::Cache is best configured to use memcache for its storage needs.
I wrote a blog post last week about the interesting way that Rack::Cache uses ETags to detect and return cached content to new clients: http://blog.craz8.com/articles/2012/12/19/rack-cache-and-etags-for-even-faster-rails
Even if you're not using Rails, the Rack middleware tools are quite good for this stuff.
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