fog-core caching class

mycache.rb

class MyCache

  def self.all(resource_klass, connection, meth, args = nil)
    cachemsg = "resource #{resource_klass} connection #{connection.class} for #{Fog::Cache.namespace_prefix}: M:#{meth} A:#{args}"

    if MyCache.renew?
      info("Renewing cache now. Cache is non existant or older than #{EXPIRE_TIME} seconds.")
      Fog::Cache.expire_cache!(resource_klass, connection)
    end

    get_from_api = lambda {
      # metaprogramming voodoo shortcut for eg: iam.users.all(iam_opts) or compute.servers.all(filters) or elb.load_balancers.all
      if args
        connection.send(meth).send(:all, args)
      else
        connection.send(meth).all
      end
    }

    if ENV['MYCACHE_NOCACHE']
      info("Force bypass using cache - querying aws directly.")
      resources = get_from_api.call

    else

    ######### BULK OF CACHE STEPS / EXAMPLE USAGE ##############

      # 1) first try to get the resources from cache:
      begin
        resources = Fog::Cache.load(resource_klass, connection)
        debug("CACHE: found cache data for #{cachemsg}") if resources

        # 1a) return if we found them in the cache
        info("Found cache for #{resource_klass}. Using this data. You can set MYCACHE_NOCACHE=1 or remove #{Fog::Cache::SANDBOX} to bypass this behavior.\n")
        return resources
      rescue Fog::Cache::CacheNotFound => e
        debug("CACHE: could not find any cache data for #{cachemsg}...trying connection.")

        # 2) not found in cache. get resources from the connection.
        resources = get_from_api.call

        # 3) dump resources for next time
        resources.each { |r| r.cache.dump }
        debug("CACHE: dumped #{resources.size} entries to cache for #{cachemsg}.")

        # 4) dump metatata for cache expirey
        Fog::Cache.write_metadata({:last_refreshed => Time.now})
        debug("CACHE: set metadata for #{Fog::Cache.namespace_prefix} to current time.")

        # 5) return resources.
        return resources
      end
    end
  end

  # set for different services/apps etc.
  def self.set_session_identifier(name)
    Fog::Cache.namespace_prefix = name
  end

  EXPIRE_TIME = (60 * 60 * 24) # day old cache.

  # renew policy cache once a day, for example.
  def self.renew?
    last_refreshed = Fog::Cache.metadata[:last_refreshed]

    if last_refreshed.nil?
      # no metadata, cache is old
      return true
    end

    if (Time.now - last_refreshed) > EXPIRE_TIME
      return true
    else
      return false
    end
  end
end

Usage:

# gets all security groups from the compute connection.
MyCache.all(Fog::Compute::AWS::SecurityGroup, compute, :security_groups, filters)

# other examples:
MyCache.all(Fog::AWS::IAM::User, iam, :users, iam_opts)
MyCache.all(Fog::Compute::AWS::Server, compute, :servers, filters)
MyCache.all(Fog::AWS::ELB::LoadBalancer, elb, :load_balancers)
MyCache.all(Fog::AWS::AutoScaling::Group, auto_scaling, :groups)