make slack alertmanager receiver more configurable

Author: sjpb

ansible/roles/alertmanager/README.md

@@ -74,6 +74,8 @@ The following variables are templated into the alertmanager [main configuration]
   mappings to add, by default empty.
 - `alertmanager_slack_receiver`: Mapping defining the [Slack receiver](https://prometheus.io/docs/alerting/latest/configuration/#slack_config). Note the default configuration for this is in
 `environments/common/inventory/group_vars/all/alertmanager.yml`.
+- `alertmanager_slack_receiver_name`: String, name for the above Slack reciever.
+- `alertmanager_slack_receiver_send_resolved`: Bool, whether to send resolved alerts via the above Slack reciever.
 - `alertmanager_null_receiver`:  Mapping defining a `null` [receiver](https://prometheus.io/docs/alerting/latest/configuration/#receiver) so a receiver is always defined.
 - `alertmanager_config_extra`: Mapping with additional configuration. Keys in
   this become top-level keys in the configuration. E.g this might be:

ansible/roles/alertmanager/defaults/main.yml

@@ -44,7 +44,7 @@ alertmanager_receivers: "{{ alertmanager_default_receivers  + alertmanager_extra
 alertmanager_config_default:
   route:
     group_by: ['...']
-    receiver: "{{ 'slack-receiver' if alertmanager_slack_integration is defined else 'null' }}"
+    receiver: "{{ alertmanager_slack_receiver_name if alertmanager_slack_integration is defined else 'null' }}"
   receivers: "{{ alertmanager_receivers }}"
 
 alertmanager_config_extra: {} # top-level only

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

@@ -1,16 +1,18 @@
 
 alertmanager_port: '9093' # defined here as required for prometheus
 
+alertmanager_slack_receiver_name: slack-receiver
+alertmanager_slack_receiver_send_resolved: true
 alertmanager_slack_receiver: # defined here as needs prometheus address
-  name: slack-receiver
+  name: "{{ alertmanager_slack_receiver_name }}"
   slack_configs:
     - channel: "{{ alertmanager_slack_integration.channel | default('none') }}"
       api_url: https://slack.com/api/chat.postMessage
       http_config:
         authorization:
           credentials: "{{ alertmanager_slack_integration.app_creds | default('none') }}"
       text: "{{ '{{' }} .GroupLabels.alertname {{ '}}' }} : {{ '{{' }}  .CommonAnnotations.description {{ '}}' }}"
-      title_link: "{{ prometheus_web_external_url }}/alerts?receiver=slack-receiver"
-      send_resolved: true
+      title_link: "{{ prometheus_web_external_url }}/alerts?receiver={{ alertmanager_slack_receiver_name }}"
+      send_resolved: "{{ alertmanager_slack_receiver_send_resolved }}"
 
 alertmanager_web_external_url: "http://{{ hostvars[groups['alertmanager'].0].ansible_host }}:{{ alertmanager_port}}/"