Add refcount extension

[ncdc]

Add refcount extension to store image references and cleanup orphans.
Based heavily on @wking's work in
#409 - this is just an
adaptation to extension format.

Signed-off-by: Andy Goldstein agoldste@redhat.com

[ncdc]

@wking @dmp42 thoughts? There are some TODOs in the extension's setup.py so I'd appreciate your input on those as well as the overall format and structure of the extension.

[ncdc]

Assuming you like this, how do we get flake8 to ignore the setup.py in the extension's folder, or do I just need to fix the file to pass the style tests?

[wking]

I haven't actually gone over the implementation yet, but I'd drop the
“[refcount]” prefix from the logger calls. If we want to prefix
logged information with module names (and I think we do) we should add
“%(name)s” to the logging.Formatter in docker_registry.wsgi. But that
would be a separate PR.

[dmp42]

@ncdc re: flake, tweak this: https://github.com/docker/docker-registry/blob/master/tox.ini#L6

[ncdc]

@wking I created a separate PR for the log format: #608

[dmp42]

Guys, like I said, I'm happy with the community owning extensions. So give me a ping when:

• things are complete
• tests are happy
• you gathered at least one LGTM review

and I'll merge (eg: don't wait for a review from me on these).

[dmp42]

I would use a separate README and LICENSE for the extension.

[ncdc]

@wking I added a license and readme for the extension. Also, I changed the author in setup.py to you, which I think makes sense if you're ok with it. I still have TODO for author_email and url...

[ncdc]

1 other thing - how would you write tests for this?

[dmp42]

@wking @ncdc where do we stand with this?

[wking]

On Tue, Dec 02, 2014 at 02:30:34PM -0800, Olivier Gambier wrote:

@wking @ncdc where do we stand with this?

Do we care about supporting this for the Python registry? Folks have
survived so far without it built in, and while I think we're still
providing maintenance for the Python implementation, I don't see the
point in investing time in adding new features there.

[matthughes]

@wking Is there a timeline for the go rewrite? I had not even heard about it until now. Just curious.

[wking]

On Tue, Dec 02, 2014 at 05:19:54PM -0800, Matt Hughes wrote:

Is there a timeline for the go rewrite?

Alpha is due 2014-11-24, and the first RC is due 2015-01-12 1.

[dmp42]

@wking I'm happy with it either way.

[ncdc]

@dmp42 we're ok closing this as long as the v2 registry supports pruning/gc in some fashion (either directly or via an extension)

[dmp42]

I believe v2 will support pruning / gc, either in core or an extension.
Now, mind the roadmap (to be updated soon by @stevvooe) - I don't expect this specific feature to land very soon (more likely sometimes down during Q1) - unless someone starts working on it sooner?