Don't show 500 errors if connection to data API fails

Some of the metrics on the instructor dashboard are computed by the new
analytics data pipeline. Don't show 500 errors if the connection to the
pipeline API fails. Instead display that the data is not available and
log an error.

AN-1476

lms/djangoapps/instructor/views/instructor_dashboard.py

@@ -2,6 +2,8 @@
 Instructor Dashboard Views
 """
 
+import logging
+
 from django.utils.translation import ugettext as _
 from django_future.csrf import ensure_csrf_cookie
 from django.views.decorators.cache import cache_control
@@ -27,12 +29,14 @@ from student.models import CourseEnrollment
 from bulk_email.models import CourseAuthorization
 from class_dashboard.dashboard_data import get_section_display_name, get_array_section_has_problem
 
-from analyticsclient.client import RestClient
+from analyticsclient.client import RestClient, ClientError
 from analyticsclient.course import Course
 
 from .tools import get_units_with_due_date, title_or_url, bulk_email_is_enabled_for_course
 from opaque_keys.edx.locations import SlashSeparatedCourseKey
 
+log = logging.getLogger(__name__)
+
 
 @ensure_csrf_cookie
 @cache_control(no_cache=True, no_store=True, must_revalidate=True)
@@ -250,22 +254,7 @@ def _section_analytics(course_key, access):
     }
 
     if settings.FEATURES.get('ENABLE_ANALYTICS_ACTIVE_COUNT'):
-        auth_token = settings.ANALYTICS_DATA_TOKEN
-        base_url = settings.ANALYTICS_DATA_URL
-
-        client = RestClient(base_url=base_url, auth_token=auth_token)
-        course = Course(client, course_key)
-
-        section_data['active_student_count'] = course.recent_active_user_count['count']
-
-        def format_date(value):
-            return value.split('T')[0]
-
-        start = course.recent_active_user_count['interval_start']
-        end = course.recent_active_user_count['interval_end']
-
-        section_data['active_student_count_start'] = format_date(start)
-        section_data['active_student_count_end'] = format_date(end)
+        _update_active_students(course_key, section_data)
 
     return section_data
 
@@ -284,3 +273,30 @@ def _section_metrics(course_key, access):
         'post_metrics_data_csv_url': reverse('post_metrics_data_csv'),
     }
     return section_data
+
+
+def _update_active_students(course_key, section_data):
+    auth_token = settings.ANALYTICS_DATA_TOKEN
+    base_url = settings.ANALYTICS_DATA_URL
+
+    section_data['active_student_count'] = 'N/A'
+    section_data['active_student_count_start'] = 'N/A'
+    section_data['active_student_count_end'] = 'N/A'
+
+    try:
+        client = RestClient(base_url=base_url, auth_token=auth_token)
+        course = Course(client, course_key)
+
+        section_data['active_student_count'] = course.recent_active_user_count['count']
+
+        def format_date(value):
+            return value.split('T')[0]
+
+        start = course.recent_active_user_count['interval_start']
+        end = course.recent_active_user_count['interval_end']
+
+        section_data['active_student_count_start'] = format_date(start)
+        section_data['active_student_count_end'] = format_date(end)
+
+    except (ClientError, KeyError) as e:
+        log.exception(e)