I'm not 100% sure how to reproduce this. I was using the Summit demo environment about 5 days after it was set up. I had:
- A repo on a CDS
- Unregister the CDS
- Re-register the CDS
- Associate the repo back to the CDS

That bombed with the following error.

Connecting to RHUA [pulp.example.com]...
Successfully connected to [pulp.example.com]
Unexpected error caught at the shell level
Traceback (most recent call last):
  File "/usr/lib/python2.7/site-packages/rhui/tools/shell.py", line 73, in safe_listen
    self.listen(clear=first_run)
  File "/usr/lib/python2.7/site-packages/rhui/tools/shell.py", line 92, in listen
    Shell.listen(self)
  File "/usr/lib/python2.7/site-packages/rhui/common/shell.py", line 191, in listen
    item.func(*args, **item.kwargs)
  File "/usr/lib/python2.7/site-packages/rhui/tools/screens/cds_repos.py", line 105, in associate
    create_performed = mode_handlers[mode](unassociated_repos)
  File "/usr/lib/python2.7/site-packages/rhui/tools/screens/cds_repos.py", line 156, in _associate_by_repo
    self.pulp.associate_repo(self.cds['hostname'], repo['id'])
  File "/usr/lib/python2.7/site-packages/rhui/tools/pulp_api.py", line 538, in associate_repo
    self.cds_api.associate(hostname, repo_id)
  File "/usr/lib/python2.7/site-packages/pulp/client/api/cds.py", line 68, in associate
    return self.server.POST(path, data)[1]
  File "/usr/lib/python2.7/site-packages/pulp/client/server.py", line 294, in POST
    return self._request('POST', path, body=body)
  File "/usr/lib/python2.7/site-packages/pulp/client/server.py", line 254, in _request
    raise ServerRequestError(response.status, response_body, None)
ServerRequestError: (409, 'Sync already in process for repo [summit-demo]', None)


It looks like it's in the associate code that attempts to trigger the redistribute. For some reason, task is coming back as None.


    def associate(self, id):
        data = self.params()
        repo_id = data.get('repo_id')
        cds_api.associate_repo(id, repo_id)

        # Kick off the async task
        task = self.start_task(cds_api.redistribute, [repo_id], unique=True)

        # If no task was returned, the uniqueness check was tripped which means
        # there's already a redistribute running for the given repo
        if task is None:
            return self.conflict('Sync already in process for repo [%s]' % repo_id)


One approach will be to ignore 409s in RHUI Manager since we know the redistribute isn't being used.