Add expected number of odcs backends

This value is mostly ignored by the application. It is included in the
Prometheus metrics to simplify calculation availability.

The default is set to 0. The number of hosts in the odcs_backend group
is used for the alternative definition in inventory.

inventory/group_vars/odcs

@@ -64,3 +64,4 @@ odcs_raw_config_urls:
     config_filename: test.conf
     url: https://pagure.io/jkaluza-test-compose.git
 primary_auth_source: ipa
+odcs_expected_backend_number: "{{ groups['odcs_backend'] | length }}"

roles/odcs/base/defaults/main.yml

@@ -49,4 +49,4 @@ odcs_seconds_to_live: 86400
 odcs_max_seconds_to_live: 259200
 odcs_celery_concurrency: 2
 odcs_extra_target_dirs: {"private": "/srv/odcs/private"}
-
+odcs_expected_backend_number: 0

roles/odcs/base/templates/etc/odcs/config.py.j2

@@ -168,3 +168,5 @@ class ProdConfiguration(BaseConfiguration):
     CELERY_ROUTER_CONFIG = {{ odcs_celery_router_config }}
 {% endif %}
 
+    EXPECTED_BACKEND_NUMBER = {{ odcs_expected_backend_number }}
+