Updated the NGINX configuration for IDAs to return a maintenance page

[LEARNER-4264]

CHANGELOG.md

+- Role edx_django_service
+  - Added maintenance page under the flag EDX_DJANGO_SERVICE_ENABLE_S3_MAINTENANCE.
+  - Added the s3_maintenance.j2 file to point to the s3 maintenance page.
+
 - Role: xqueue
   - Added XQUEUE_MYSQL_CONN_MAX_AGE so that you can have xqueue use django's persistent DB connections
+
 - Role: edxapp
   - Added empty `EDXAPP_PASSWORD_COMPLEXITY` setting to ease overriding complexity.
 

playbooks/roles/edx_django_service/defaults/main.yml

@@ -68,6 +68,10 @@ nginx_edx_django_service_gunicorn_hosts:
 
 edx_django_service_hostname: '~^((stage|prod)-)?{{ edx_django_service_name }}.*'
 edx_django_service_nginx_port: '1{{ edx_django_service_gunicorn_port }}'
+
+EDX_DJANGO_SERVICE_ENABLE_S3_MAINTENANCE: true
+EDX_DJANGO_SERVICE_S3_MAINTENANCE_FILE: "/edx-static/maintenance/maintenance.html"
+
 edx_django_service_ssl_nginx_port: '4{{ edx_django_service_gunicorn_port }}'
 edx_django_service_enable_basic_auth: false
 edx_django_service_basic_auth_exempted_paths_default:

playbooks/roles/edx_django_service/templates/edx/app/nginx/sites-available/app.j2

@@ -30,6 +30,16 @@ default "null";
 server {
   server_name {{ edx_django_service_hostname }};
 
+  {% if EDX_DJANGO_SERVICE_ENABLE_S3_MAINTENANCE %}
+  # Do not include a 502 error in NGINX_ERROR_PAGES when 
+  # EDX_DJANGO_SERVICE_ENABLE_S3_MAINTENANCE is enabled.
+  
+  error_page 502 @maintenance;
+
+    {% include "s3_maintenance.j2" %}
+
+  {% endif %}
+
   {% if NGINX_ENABLE_SSL %}
 
   listen {{ edx_django_service_nginx_port }} {{ default_site }};

playbooks/roles/edx_django_service/templates/edx/app/nginx/sites-available/s3_maintenance.j2

+# This file was copied from playbooks/roles/nginx/templates/edx/app/nginx/sites-available/
+# modifications should be made to both files if necessary.
+
+{% if EDX_DJANGO_SERVICE_ENABLE_S3_MAINTENANCE %}
+location @maintenance {
+    rewrite  ^(.*) {{ EDX_DJANGO_SERVICE_S3_MAINTENANCE_FILE }} break;
+    proxy_http_version     1.1;
+    proxy_set_header       Host s3.amazonaws.com;
+    proxy_set_header       Authorization '';
+    proxy_hide_header      x-amz-id-2;
+    proxy_hide_header      x-amz-request-id;
+    proxy_hide_header      Set-Cookie;
+    proxy_ignore_headers   "Set-Cookie";
+    proxy_buffering        off;
+    proxy_intercept_errors on;
+    proxy_pass https://s3.amazonaws.com;
+}
+{% endif %}