prometheus: mention Thanos in docs

roles/prometheus/README.md

@@ -16,6 +16,9 @@ silences one should use "amtool" inside the container, i.e.:
 $ in-container prometheus-alertmanager amtool alert
 ```
 
+On the read path, [Thanos](https://thanos.io) is used to merge results from
+multiple Prometheus instances.
+
 ## Customizing alerts
 
 A few alerting rules are provided by default

services.yml.no-elasticsearch

@@ -101,7 +101,7 @@ prometheus:
       port: 2929
       scheme: https
       enable_sso_proxy: true
-    - name: thanos-query
+    - name: thanos
       port: 10902
       scheme: http
       enable_sso_proxy: true

test/float_integration_test/test_system.py

@@ -53,6 +53,9 @@ class TestBuiltinServiceURLs(URLTestBase):
     def test_grafana(self):
         self._assert_endpoint_ok_if_enabled('prometheus', 'grafana')
 
+    def test_thanos(self):
+        self._assert_endpoint_ok_if_enabled('prometheus', 'thanos')
+
     def test_kibana(self):
         if not ANSIBLE_VARS.get('enable_elasticsearch', True):
             self.skipTest('Elasticsearch is disabled')