Plugin-based dashboard configuration

This is a proof of concept of how plugin-based configuration of
OpenStack dashboards could be realized. Additional plugins add
their configuration file in the opestack_dashboard/enabled/
directory (the exact location is up for discussion, we will
probably want a whole hierarchy of locations, with the possibility
of overriding settings).

An example file _50_tuskar.py is added to show how an additional
dashboard could plug into this system. If you have tuskar_ui installed,
this would add Tuskar to Horizon.

Change-Id: Iaa594deffbdb865116f6f62855c32c8633d2b208
Implements: blueprint plugin-architecture

doc/source/topics/settings.rst

@@ -338,3 +338,75 @@ generate a secret key for a single installation.
 These three settings should be configured if you are deploying Horizon with
 SSL. The values indicated in the default ``local_settings.py.example`` file
 are generally safe to use.
+
+
+Pluggable Settings for Dashboards
+=================================
+
+Many dashboards may require their own modifications to the settings, and their
+installation would therefore require modifying the settings file. This is not
+optimal, so the dashboards can provide the settings that they require in a
+separate file. Those files are read at startup and used to modify the default
+settings.
+
+The default location for the dashboard configuration files is
+``openstack_dashboard/enabled``, with another directory,
+``openstack_dashboarrd/local/enabled`` for local overrides. Both sets of files
+will be loaded, but the settings in ``openstack_dashboard/local/enabled`` will
+overwrite the default ones. The settings are applied in alphabetical order of
+the filenames. If the same dashboard has configuration files in ``enabled`` and
+``local/enabled``, the local name will be used. Note, that since names of
+python modules can't start with a digit, the files are usually named with a
+leading underscore and a number, so that you can control their order easily.
+
+The files contain following keys:
+
+``DASHBOARD``
+-------------
+
+The name of the dashboard to be added to ``HORIZON['dashboards']``. Required.
+
+``DEFAULT``
+-----------
+
+If set to ``True``, this dashboard will be set as the default dashboard.
+
+``ADD_EXCEPTIONS``
+------------------
+
+A dictionary of exception classes to be added to ``HORIZON['exceptions']``.
+
+``ADD_INSTALLED_APPS``
+----------------------
+
+A list of applications to be added to ``INSTALLED_APPS``.
+
+``DISABLED``
+------------
+
+If set to ``True``, this dashboard will not be added to the settings.
+
+Examples
+--------
+
+To disable the Router dashboard locally, create a file
+``openstack_dashboard/local/enabled/_40_router.py`` with the following
+content::
+
+    DASHBOARD = 'router'
+    DISABLED = True
+
+To add a Tuskar-UI (Infrastructure) dashboard, you have to install it, and then
+create a file ``openstack_dashboard/local/enabled/_50_tuskar.py`` with::
+
+    from tuskar_ui import exceptions
+
+    DASHBOARD = 'infrastructure'
+    ADD_INSTALLED_APPS = [
+        'tuskar_ui.infrastructure',
+    ]
+    ADD_EXCEPTIONS = {
+        'recoverable': exceptions.RECOVERABLE,
+        'not_found': exceptions.NOT_FOUND,
+        'unauthorized': exceptions.UNAUTHORIZED,
+    }

openstack_dashboard/enabled/_10_project.py

@@ -0,0 +1,8 @@
+# The name of the dashboard to be added to HORIZON['dashboards']. Required.
+DASHBOARD = 'project'
+# If set to True, this dashboard will be set as the default dashboard.
+DEFAULT = True
+# A dictionary of exception classes to be added to HORIZON['exceptions'].
+ADD_EXCEPTIONS = {}
+# A list of applications to be added to INSTALLED_APPS.
+ADD_INSTALLED_APPS = ['openstack_dashboard.dashboards.project']

openstack_dashboard/enabled/_20_admin.py

@@ -0,0 +1,7 @@
+# The name of the dashboard to be added to HORIZON['dashboards']. Required.
+DASHBOARD = 'admin'
+
+# A list of applications to be added to INSTALLED_APPS.
+ADD_INSTALLED_APPS = [
+    'openstack_dashboard.dashboards.admin',
+]

openstack_dashboard/enabled/_30_settings.py

@@ -0,0 +1,7 @@
+# The name of the dashboard to be added to HORIZON['dashboards']. Required.
+DASHBOARD = 'settings'
+
+# A list of applications to be added to INSTALLED_APPS.
+ADD_INSTALLED_APPS = [
+    'openstack_dashboard.dashboards.settings',
+]

openstack_dashboard/enabled/_40_router.py

@@ -0,0 +1,10 @@
+# The name of the dashboard to be added to HORIZON['dashboards']. Required.
+DASHBOARD = 'router'
+
+# A list of applications to be added to INSTALLED_APPS.
+ADD_INSTALLED_APPS = [
+    'openstack_dashboard.dashboards.router',
+]
+
+# If set to True, this dashboard will not be added to the settings.
+DISABLED = True

openstack_dashboard/local/enabled/_40_router.py.example

@@ -0,0 +1,5 @@
+# The name of the dashboard to be added to HORIZON['dashboards']. Required.
+DASHBOARD = 'router'
+
+# If set to True, this dashboard will not be added to the settings.
+DISABLED = False

openstack_dashboard/settings.py

@@ -145,7 +145,7 @@ COMPRESS_OUTPUT_DIR = 'dashboard'
 COMPRESS_CSS_HASHING_METHOD = 'hash'
 COMPRESS_PARSER = 'compressor.parser.HtmlParser'
 
-INSTALLED_APPS = (
+INSTALLED_APPS = [
     'openstack_dashboard',
     'django.contrib.contenttypes',
     'django.contrib.auth',
@@ -160,7 +160,7 @@ INSTALLED_APPS = (
     'openstack_dashboard.dashboards.settings',
     'openstack_auth',
     'openstack_dashboard.dashboards.router',
-)
+]
 
 TEST_RUNNER = 'django_nose.NoseTestSuiteRunner'
 AUTHENTICATION_BACKENDS = ('openstack_auth.backend.KeystoneBackend',)
@@ -210,6 +210,17 @@ try:
 except ImportError:
     logging.warning("No local_settings file found.")
 
+# Load the pluggable dashboard settings
+import openstack_dashboard.enabled
+import openstack_dashboard.local.enabled
+from openstack_dashboard.utils import settings
+
+INSTALLED_APPS = list(INSTALLED_APPS)  # Make sure it's mutable
+settings.update_dashboards([
+    openstack_dashboard.enabled,
+    openstack_dashboard.local.enabled,
+], HORIZON_CONFIG, INSTALLED_APPS)
+
 # Ensure that we always have a SECRET_KEY set, even when no local_settings.py
 # file is present. See local_settings.py.example for full documentation on the
 # horizon.utils.secret_key module and its use.

openstack_dashboard/utils/settings.py

@@ -0,0 +1,92 @@
+# vim: tabstop=4 shiftwidth=4 softtabstop=4
+
+#    Licensed under the Apache License, Version 2.0 (the "License"); you may
+#    not use this file except in compliance with the License. You may obtain
+#    a copy of the License at
+#
+#         http://www.apache.org/licenses/LICENSE-2.0
+#
+#    Unless required by applicable law or agreed to in writing, software
+#    distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+#    WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+#    License for the specific language governing permissions and limitations
+#    under the License.
+
+import collections
+import logging
+import pkgutil
+
+from django.utils import importlib
+
+
+def import_submodules(module):
+    """Import all submodules and make them available in a dict."""
+    submodules = {}
+    for loader, name, ispkg in pkgutil.iter_modules(module.__path__,
+                                                    module.__name__ + '.'):
+        try:
+            submodule = importlib.import_module(name)
+        except ImportError as e:
+            # FIXME: Make the errors non-fatal (do we want that?).
+            logging.warning("Error importing %s" % name)
+            logging.exception(e)
+        else:
+            parent, child = name.rsplit('.', 1)
+            submodules[child] = submodule
+    return submodules
+
+
+def import_dashboard_config(modules):
+    """Imports configuration from all the modules and merges it."""
+    config = collections.defaultdict(dict)
+    for module in modules:
+        for key, submodule in import_submodules(module).iteritems():
+            try:
+                dashboard = submodule.DASHBOARD
+            except AttributeError:
+                logging.warning("Skipping %s because it doesn't "
+                                "have DASHBOARD defined." % submodule.__name__)
+            else:
+                config[dashboard].update(submodule.__dict__)
+    return sorted(config.iteritems(),
+                  key=lambda c: c[1]['__name__'].rsplit('.', 1))
+
+
+def update_dashboards(modules, horizon_config, installed_apps):
+    """Imports dashboard configuration from modules and applies it.
+
+    The submodules from specified modules are imported, and the configuration
+    for the specific dashboards is merged, with the later modules overriding
+    settings from the former. Then the configuration is applied to
+    horizon_config and installed_apps, in alphabetical order of files from
+    which the configurations were imported.
+
+    For example, given this setup:
+
+        foo/__init__.py
+        foo/_10_baz.py
+        foo/_20_qux.py
+
+        bar/__init__.py
+        bar/_30_baz_.py
+
+    and being called with ``modules=[foo, bar]``, we will first have the
+    configuration from ``_10_baz`` and ``_30_baz`` merged, then the
+    configurations will be applied in order ``qux``, ``baz`` (``baz`` is
+    second, because the most recent file which contributed to it, ``_30_baz``,
+    comes after ``_20_qux``).
+    """
+    dashboards = []
+    exceptions = {}
+    apps = []
+    for dashboard, config in import_dashboard_config(modules):
+        if config.get('DISABLED', False):
+            continue
+        dashboards.append(dashboard)
+        exceptions.update(config.get('ADD_EXCEPTIONS', {}))
+        apps.extend(config.get('ADD_INSTALLED_APPS', []))
+        if config.get('DEFAULT', False):
+            horizon_config['default_dashboard'] = dashboard
+    horizon_config['dashboards'] = tuple(dashboards)
+    horizon_config['exceptions'].update(exceptions)
+    installed_apps.extend(apps)