fix: alert mail template (#11)

- Fix the template file name: write all custom templates into custom.tmpl. - Use the template name as a prefix for the subparts definition Refs NethServer/dev#7162
NethServer · Mar 5, 2025 · e2274eb · e2274eb
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diff --git a/README.md b/README.md
@@ -117,19 +117,17 @@ Logs page, searching for YAML parse errors.
 **This is an experimental feature, do not use in production.**
 Configuration may change on the future releases.
 
-You can change the mail template used to send alerts by creating a custom template in the `templates.d` directory.
+First, create a template file, for example `myalert.tmpl`. Make sure to
+define `myalert_subject` and `myalert_html` sections, as they are
+used by the module to render the mail. For additional information refer to
+[Alertmanager
+documentation](https://prometheus.io/docs/alerting/latest/notification_examples/).
 
-First, create a template.
-Make sure to not change `custom_mail_subject` and `custom_mail_html` names, as they are used by the module to render the mail.
-Execute the following commands:
-```
-echo '<template>' | redis-cli -x hset module/metrics1/custom_templates <template_name>
-```
+Example of `myalert.tmpl` contents:
 
-Example:
-```
-echo '{{ define "custom_mail_subject" }}Alert on {{ range .Alerts.Firing }}{{ .Labels.instance }} {{ end }}{{ end }}
-{{ define "custom_mail_html" }}
+```text
+{{ define "myalert_subject" }}Alert on {{ range .Alerts.Firing }}{{ .Labels.instance }} {{ end }}{{ end }}
+{{ define "myalert_html" }}
 <html>
 <head>
 <title>Alert!</title>
@@ -151,24 +149,25 @@ echo '{{ define "custom_mail_subject" }}Alert on {{ range .Alerts.Firing }}{{ .L
 </p>
 {{ end }}
 </body></html>
-{{ end }}' | redis-cli -x hset module/metrics2/custom_templates mail
+{{ end }}
 ```
 
-Apply the changes:
+Load the template file in Redis DB:
+
 ```
-runagent -m metrics1 systemctl --user restart prometheus alertmanager
+redis-cli -x hset module/metrics1/custom_templates myalert <myalert.tmpl
 ```
 
-Then, configure the module to use the new template:
+Configure the module to use the new template:
 ```
-api-cli run module/metrics1/configure-module --data '{"prometheus_path": "prometheus", "grafana_path": "grafana", "mail_from": "[email protected]", "mail_to": ["[email protected]"], "mail_template": "custom_mail_html"}'
+api-cli run module/metrics1/configure-module --data '{"prometheus_path": "prometheus", "grafana_path": "grafana", "mail_from": "[email protected]", "mail_to": ["[email protected]"], "mail_template": "myalert"}'
 ```
 
 You can test the template rendering using the following command:
 ```
 runagent -m metrics1
-podman exec -ti alertmanager amtool template render --template.glob='/etc/alertmanager/templates/*.tmpl' --template.text='{{ template "custom_mail_html" . }}'
-podman exec -ti alertmanager amtool template render --template.glob='/etc/alertmanager/templates/*.tmpl' --template.text='{{ template "custom_mail_subject" . }}'
+podman exec -ti alertmanager amtool template render --template.glob='/etc/alertmanager/templates/*.tmpl' --template.text='{{ template "myalert_html" . }}'
+podman exec -ti alertmanager amtool template render --template.glob='/etc/alertmanager/templates/*.tmpl' --template.text='{{ template "myalert_subject" . }}'
 ```
 
 ## Testing

diff --git a/imageroot/bin/reload_configuration b/imageroot/bin/reload_configuration
@@ -130,8 +130,11 @@ def generate_alertmanagr_config(redis_client):
             'to': config['mail_to']
         }
         if 'mail_template' in config and config['mail_template']:
-            mail_config['html'] = '{{ template "custom_mail_html" . }}'
-            mail_config['headers'] = { 'subject': '{{ template "custom_mail_subject" . }}' }
+            template_key = config['mail_template']
+            mail_config['html'] = '{{{{ template "{}_html" . }}}}'.format(template_key)
+            mail_config['headers'] = {
+                'subject': '{{{{ template "{}_subject" . }}}}'.format(template_key),
+            }
         alert_config['receivers'].append({
             'email_configs': [ mail_config ],
             'name': 'mail-alert'
@@ -166,16 +169,11 @@ def generate_custom_alertmanager_rules(redis_client):
             pass
 
 def generate_custom_alertmanager_templates(redis_client):
-    # Search for all custom_*.yml files, delete the ones that are not in the nodes list
-    with os.scandir('templates.d') as it:
-        for entry in it:
-            if entry.is_file() and entry.name.startswith('custom_') and entry.name not in nodes:
-                os.remove(entry.path)
-    for key in redis_client.hgetall(f'module/{os.environ["MODULE_ID"]}/custom_templates'):
-        template = redis_client.hget(f'module/{os.environ["MODULE_ID"]}/custom_templates', key)
-        if template:
-            with open(f'templates.d/custom_{key}.yml', 'w') as f:
-                f.write(template + '\n')
+    # Custom template declarations are concatenated in the same file:
+    with open(f'templates.d/custom.tmpl', 'w') as f:
+        for template in redis_client.hvals(f'module/{os.environ["MODULE_ID"]}/custom_templates'):
+            if template:
+                f.write(template)
 
 # connect to client and fetch providers for prometheus
 redis_client = agent.redis_connect(use_replica=True)