Bug/ruler use wrong alertmanager url (#594)

* Fix alertmanager URL template in ruler-dep.yaml

Use the same method as alertmanager-headless-service to generate hostname

Signed-off-by: Amirul Ali <amirul@rixv.net>

* Add bugfix entry for Alertmanager URL issue

Signed-off-by: Amirul Ali <amirul@rixv.net>

---------

Signed-off-by: Amirul Ali <amirul@rixv.net>
Co-authored-by: Tom Hayward <thayward@infoblox.com>

Author: amirulali

CHANGELOG.md

@@ -6,6 +6,7 @@
 * [ENHANCEMENT] Avoid scheduling queriers and ingesters on the same node #583
 * [ENHANCEMENT] Allow for the nginx service port and container port to be different #589
 * [DEPENDENCY] Update quay.io/cortexproject/cortex Docker tag to v1.20.1 #577
+* [BUGFIX] Ruler is using the wrongly generated Alertmanager URL #593
 
 ## 3.0.0 / 2025-11-27
 

templates/ruler/ruler-dep.yaml

@@ -107,7 +107,7 @@ spec:
             - "-config.file=/etc/cortex/cortex.yaml"
             {{- if not .Values.config.ruler.alertmanager_url }}
               {{- if .Values.config.ruler.enable_alertmanager_discovery }}
-            - "-ruler.alertmanager-url=http://_http-metrics._tcp.{{ template "cortex.name" . }}-alertmanager-headless.{{ .Release.Namespace }}.svc.{{ .Values.clusterDomain }}/api/prom/alertmanager/"
+            - "-ruler.alertmanager-url=http://_http-metrics._tcp.{{ template "cortex.alertmanagerFullname" . }}-headless.{{ .Release.Namespace }}.svc.{{ .Values.clusterDomain }}/api/prom/alertmanager/"
               {{- else }}
             - "-ruler.alertmanager-url=http://{{ template "cortex.alertmanagerFullname" . }}.{{ .Release.Namespace }}.svc.{{ .Values.clusterDomain }}:{{ .Values.config.server.http_listen_port }}/api/prom/alertmanager/"
               {{- end }}