Details about HTTP Headers Caching module

Here are some details about the module that we want to sponsor
development for:

  1. We want to use nginx as a reverse proxy for a Domain Forwarding
    Service
  2. This would require nginx to cache responses that contain only headers
    and no body (301 HTTP responses)
  3. We also need a way to invalidate caches. This should ideally be a
    command line tool.

Regards,

Latesh Galia
Software Engineer,
Directi

http://www.directi.com

Hi Latesh,

Thanks for the information.

I have some further questions, mostly to give me a clearer idea of your
aims.

  1. Are you only looking at caching redirection (i.e. 3xx) responses?
  2. Are you looking to cache the responses in memory, on disk, or both?
  3. When you say ‘invalidate’, do you mean purge (i.e. remove the cached
    entry from the cache)?
  4. How are you intending on purging the caches? Here are some possible
    ways with pros/cons
  • using ttl’s (expiry times) for each cached object individually
    Pros : provides the most granularity and will probably give the
    smoothest load to backends
    Cons : adds slight overhead to the request, and complexity in
    writing it (if the caching part is done from scratch)

  • purging all objects at once whenever you wanted
    Pros : very simple to implement
    Cons : might cause a temporary rush on the backends when objects are
    purged

  • purging a subsection of the objects on a regular basis (e.g. 1/32 of
    the objects every 30 mins)
    Pros : very simple to implement, much less of a rush on backends
    after purges
    Cons : limited granularity

  1. How many objects are we looking at caching roughly? thousands,
    millions, tens/hundreds of millions?

  2. How many worker processes do you/will you use on the Nginx
    installation (if you use more than 1, then this adds complexity to the
    caching process, and makes memory caching a pain - to the extent that
    you might as well use memcached for it).

  3. Are you definitely looking at having an internal cache, or would you
    be happy with using memcached? One idea I thought of is to check for
    cached pages memcached first for a cached header, then serving from the
    backend if no header-only object is found. A header-only response would
    then put the object in memcached.
    Pros : you could put objects/control the cache separately to the
    Nginx installation, perhaps saving some overhead
    Cons : for non-header-only objects, there would be the slight extra
    overhead of checking memcached on each request (which would obviously be
    slower than using an in-memory cache)

  4. What kind of load does your server get (average req/s etc)?

I will probably have a few more questions later, but the answers to the
above should give me a better idea of what you want, and give me a
better idea of a good way to implement your task.

Regards,

Marcus.

Hi Latesh,

One more question : what operating system do you run on the server(s)
that will have Nginx on?

Thanks,

Marcus.

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