fix up prom address in slack alert links

Author: sjpb

ansible/roles/alertmanager/README.md

@@ -134,6 +134,7 @@ Swap:             0B          0B          0B
 
         /invite @YOUR_BOT_NAME
 
+TODO: note that `prometheus_web_external_url` might need overriding too.
 
 ## Alert Rules
 

environments/common/inventory/group_vars/all/alertmanager.yml

@@ -10,5 +10,5 @@ alertmanager_slack_receiver: # defined here as needs prometheus address
         authorization:
           credentials: "{{ alertmanager_slack_integration.app_creds | default('none') }}"
       text: "{{ '{{' }} .GroupLabels.alertname {{ '}}' }} : {{ '{{' }}  .CommonAnnotations.description {{ '}}' }}"
-      title_link: "http://{{ prometheus_address }}:9090/alertmanager/#/alerts?receiver=slack-receiver"
+      title_link: "{{ prometheus_web_external_url }}/alerts?receiver=slack-receiver"
       send_resolved: true

environments/common/inventory/group_vars/all/prometheus.yml

@@ -4,7 +4,7 @@
 # for variable definitions
 
 prometheus_version: 2.27.0 # default from ansible/roles/cloudalchemy.prometheus/defaults/main.yml
-prometheus_web_external_url: "http://{{ prometheus_address }}:9090"
+prometheus_web_external_url: "http://{{ hostvars[groups['prometheus'].0].ansible_host }}:9090/" # default to host IP address
 prometheus_storage_retention: "31d"
 prometheus_storage_retention_size: "100GB"
 prometheus_db_dir: "{{ appliances_state_dir | default('/var/lib') }}/prometheus"