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The image caching configuration is somewhat unique within Glance, as it is needed by multiple wsgi apps. As you point out, that means you need to duplicate your cache configuration in glance-api.conf and glance-cache.conf to get everything to play well together. I'm going to update the docs to make that point clear, and I'll also file a bug on the issue of unnecessary duplication.

Brian


On Mar 14, 2012, at 5:06 AM, Eoghan Glynn wrote:

> 
> 
>> Yes, it does make perfect sense. Kind thanks for the explanation.
>> 
>> However, what is still unclear is what config iteems that pertain to
>> other apps must still be present (ie. duplicated in) glance-api.conf
>> (e.g. image_cache_driver , etc )
> 
> 
> This is probably something we should document more carefully so it's clear
> to users from the outset which config options are required and when. 
> 
> However I don't have a definitive mapping of config items to apps, so I'd
> normally consider them on a case-by-case basis and just check where the config
> option is used. For example it may be always required by a particular app, or
> only be required if a particular middleware is enabled.
> 
> In this particular case, a little grep'ing in the codebase soon reveals when
> the image_cache_driver config item is required. 
> 
> $ find glance -name "*.py" | grep -v test | xargs grep -n -B 5 image_cache_driver
> glance/image_cache/__init__.py-33-class ImageCache(object):
> glance/image_cache/__init__.py-34-
> glance/image_cache/__init__.py-35-    """Provides an LRU cache for image data."""
> glance/image_cache/__init__.py-36-
> glance/image_cache/__init__.py-37-    opts = [
> glance/image_cache/__init__.py:38:        cfg.StrOpt('image_cache_driver', default='sqlite'),
> --
> glance/image_cache/__init__.py-48-
> glance/image_cache/__init__.py-49-    def init_driver(self):
> glance/image_cache/__init__.py-50-        """
> glance/image_cache/__init__.py-51-        Create the driver for the cache
> glance/image_cache/__init__.py-52-        """
> glance/image_cache/__init__.py:53:        driver_name = self.conf.image_cache_driver
> 
> So we see that this config option is pulled in by the glance.image_cache.ImageCache
> class, which is then used as follows:
> 
> $ find glance -name "*.py"  | grep -v test | xargs grep ImageCache | cut -f1 -d: | sort | uniq
> glance/api/cached_images.py
> glance/api/middleware/cache.py
> glance/image_cache/cleaner.py
> glance/image_cache/__init__.py
> glance/image_cache/prefetcher.py
> glance/image_cache/pruner.py
> glance/image_cache/queue_image.py
> 
> Looking the first two source files, we see that the image_cache_driver config option
> would be required in the glance-api application iff a caching or cachemanagement-based
> pipeline is selected.
> 
> Cheers,
> Eoghan
> 
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