Starting docker-registry results in error 'ImportError: No module named sqlalchemy'

Issue

• Starting docker-registry service results in the following error:

2015-04-22 15:22:42 [12345] [WARNING] debug mode: app isn't preloaded.
2015-04-22 15:22:42 [12345] [INFO] Starting gunicorn 18.0
2015-04-22 15:22:42 [12345] [INFO] Listening at: http://0.0.0.0:5000 (30762)
2015-04-22 15:22:42 [12345] [INFO] Using worker: gevent
2015-04-22 15:22:42 [12345] [INFO] Booting worker with pid: 30767
2015-04-22 15:22:42 [12345] [INFO] Booting worker with pid: 30768
2015-04-22 15:22:42 [12345] [INFO] Booting worker with pid: 30769
2015-04-22 15:22:43 [12345] [INFO] Booting worker with pid: 30782
2015-04-22 15:22:43 [12345] [ERROR] Exception in worker process:
Traceback (most recent call last):
  File "/usr/lib/python2.7/site-packages/gunicorn/arbiter.py", line 495, in spawn_worker
    worker.init_process()
  File "/usr/lib/python2.7/site-packages/gunicorn/workers/base.py", line 106, in init_process
    self.wsgi = self.app.wsgi()
  File "/usr/lib/python2.7/site-packages/gunicorn/app/base.py", line 114, in wsgi
    self.callable = self.load()
  File "/usr/lib/python2.7/site-packages/gunicorn/app/wsgiapp.py", line 62, in load
    return self.load_wsgiapp()
  File "/usr/lib/python2.7/site-packages/gunicorn/app/wsgiapp.py", line 49, in load_wsgiapp
    return util.import_app(self.app_uri)
  File "/usr/lib/python2.7/site-packages/gunicorn/util.py", line 354, in import_app
    __import__(module)
  File "/usr/lib/python2.7/site-packages/docker-registry/docker_registry/__init__.py", line 21, in <module>
    from .search import *
  File "/usr/lib/python2.7/site-packages/docker-registry/docker_registry/search.py", line 14, in <module>
    INDEX = index.load(cfg.search_backend.lower())
  File "/usr/lib/python2.7/site-packages/docker-registry/docker_registry/lib/index/__init__.py", line 78, in load
    from . import db
  File "/usr/lib/python2.7/site-packages/docker-registry/docker_registry/lib/index/db.py", line 4, in <module>
    import sqlalchemy
ImportError: No module named sqlalchemy