Horizon broken for multi region setup

[Mathieu Goessens]

Hi,

Devstack supports multi-region setup according to https://docs.openstack.org/devstack/latest/configuration.html#multi-region-setup.

However, when using this setup, with a stable/queens (did not test master branch), user may be unable to log into horizon. The following message is displayed in /var/log/apache2/horizon_error.log :

--- snip ---
2018-07-10 13:06:52.280635 ERROR openstack_auth.backend Using signed cookies as SESSION_ENGINE with OPENSTACK_KEYSTONE_MULTIDOMAIN_SUPPORT is enabled. This disables the ability to perform identity operations due to cookie size constraints.
--- snip ---

User can manually change the session engine and the cache backend by editing /opt/stack/horizon/openstack_dashboard/settings.py, adding the following lines at the end (SESSION_ENGINE may be already being defined earlier) and restarting apache

--- snip ---
SESSION_ENGINE = 'django.contrib.sessions.backends.cache'

CACHES = {
    'default': {
        'BACKEND': 'django.core.cache.backends.filebased.FileBasedCache',
        'LOCATION': '/var/tmp/django_cache',
    }
}
--- snip ---

It may be nice that devstack automatically perform this kind of configuration (maybe with a better cache backend) when the REGION_NAME, KEYSTONE_REGION_NAME, or MULTI_REGION are changed, or at least to document it in https://docs.openstack.org/devstack/latest/configuration.html#multi-region-setup (as it may be hard to detect when a region is added).

Cheers,

[Mathieu Goessens (gebura)]

For the sake of the completeness: no message is displayed in the horizon dashboard, the user is only redirected again and again to the login form, making it hard to understand what the problem could be.

[Michael J Burling (mburling)]

Aside from the inconvenience posed by changing this setting manually, I haven't looked too closely at the differences between the session engines, and I'm not sure if selecting `django.contrib.sessions.backends.cache` is a mistake for other reasons. Can anyone confirm that this is an acceptable workaround in the interim? Thanks!

[Ivan Kolodyazhny (e0ne)]

It looks like a configuration issue which should be fixed in devstack

[Dr. Jens Harbott (j-harbott)]

Is this still happening? I think we would consider marking this as unsupported unless anyone submits a fix.

[Launchpad Janitor (janitor)]

[Expired for devstack because there has been no activity for 60 days.]