Horizon relies on Keystone to provide authentication services. As such you must have installed Keystone [1] and created a user [2]. Horizon determines where to look for the Keystone server using the OPENSTACK_KEYSTONE_URL configuration key in the local_settings.py file:

OPENSTACK_HOST = "127.0.0.1"
OPENSTACK_KEYSTONE_URL = "http://%s:5000/v2.0" % OPENSTACK_HOST

It then attempts to authenticate with the Keystone server using the credentials you provide on the login screen. You do not need to deploy all of the other services to be able to run/access Horizon, just Keystone, however the tabs and actions available in Horizon will vary based on what services are installed.

The Network tab for example is only available if Quantum / Neutron is installed and configured in your environment. Horizon detects what services are available based on the service endpoints defined in Keystone, once authenticated.

[1] http://docs.openstack.org/developer/keystone/installing.html [2] http://docs.openstack.org/trunk/openstack-compute/admin/content/adding-users-tenants-and-roles-with-python-keystoneclient.html

You can't install Horizon on its own. As explained in the Quickstart docs you linked to, it requires at least Keystone (for authentication), Nova and Glance (for launching instances) to be installed.

From http://docs.openstack.org/developer/horizon/quickstart.html :

The minimum required set of OpenStack services running includes the following:

Nova (compute, api, scheduler, and network)

Glance

Keystone