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[Vishvananda Ishaya <vishvananda@xxxxxxxxx>]

Metadata is supposed to be user "tags" that are associated with a guest
that are available via the api. We discussed displaying these tags inside
the guest as well.

The main difference between user-data and metadata is that metadata is
available to the api, whereas user-data is only available in the guest.

Vish

On Jul 3, 2012, at 10:05 AM, Scott Moser wrote:

> Hi,
> I'm looking at nova, and the compute API has 3 methods:
>   delete_instance_metadata
>   update_instance_metadata
>   get_instance_metadata
> 
> I know that
> * python nova client has
>   * the ability to specify --meta=KEY=VALUE on instance creation
>   * a top level subcommand 'meta' which allows set and delete of
>     metadata keys (but no support for querying current value).
> * content specified on instance creation is injected into the
>   instance's root filesystem at '/meta.js'.  Or, if config_drive
>   is given the config drive will have /meta.js
> 
> What I'm missing is:
> * There is an 'update' for this content, implying that it is at least
>   partially dynamic in intent, but the filesystem data passing mechanism
>   is clearly *not* dynamic.
> * This data is not made available in the metadata server
>   (http://169.254.169.254) where it *could* be dynamic.
> 
> So, I'm confused on the intent of this metadata.  I can't decide if it is
> really just supposed to be "tags" or more of a user-data replacement.
> 
> In EC2, you can store arbitrary key/value pairs on an instance-id,
> ami-id, or anything else, but those values are not readable without
> credentials.  Here, they're readable inside the instance from the
> filesystem.
> 
> Anyone able to comment on the original intent of 'metadata'?
> It seems to me that if we expose this in the metadata server, then it will
> be a very useful feature, but one that overlaps confusingly with
> user-data.
> 
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