feat(monitoring): add Alertmanager with Slack notifications

- config/alertmanager/alertmanager.yml: route, slack-default and null receivers
- config/prometheus.yml: alerting.alertmanagers -> alertmanager:9093
- docker-compose.prod.yml: alertmanager service (port 9093)

config/alertmanager/alertmanager.yml

@@ -0,0 +1,24 @@
+# Alertmanager config for Veza
+# For Slack: override this file with your SLACK_WEBHOOK_URL in api_url
+global:
+  resolve_timeout: 5m
+
+route:
+  receiver: 'null'
+  group_by: ['alertname', 'job']
+  group_wait: 30s
+  group_interval: 5m
+  repeat_interval: 4h
+
+receivers:
+  - name: 'slack-default'
+    slack_configs:
+      - api_url: '${SLACK_WEBHOOK_URL}'
+        channel: '#alerts'
+        send_resolved: true
+        title: '{{ .Status | toUpper }}: {{ .GroupLabels.alertname }}'
+        text: '{{ range .Alerts }}{{ .Annotations.description }}{{ end }}'
+
+  - name: 'null'
+    # Default: alerts received but not sent. Set route.receiver to slack-default
+    # and SLACK_WEBHOOK_URL env when Slack is configured.

config/prometheus.yml

@@ -2,6 +2,11 @@ global:
   scrape_interval: 15s
   evaluation_interval: 15s
 
+alerting:
+  alertmanagers:
+    - static_configs:
+        - targets: ['alertmanager:9093']
+
 rule_files:
   - "prometheus/alert_rules.yml"
 

docker-compose.prod.yml

@@ -337,6 +337,26 @@ services:
     networks:
       - veza-network
 
+  # ============================================================================
+  # MONITORING - Alertmanager
+  # Set SLACK_WEBHOOK_URL for Slack notifications. Works with Prometheus.
+  # ============================================================================
+  alertmanager:
+    image: prom/alertmanager:v0.26.0
+    container_name: veza_alertmanager
+    restart: unless-stopped
+    ports:
+      - "9093:9093"
+    volumes:
+      - ./config/alertmanager/alertmanager.yml:/etc/alertmanager/alertmanager.yml:ro
+    command:
+      - '--config.file=/etc/alertmanager/alertmanager.yml'
+      - '--storage.path=/alertmanager'
+    environment:
+      - SLACK_WEBHOOK_URL=${SLACK_WEBHOOK_URL:-}
+    networks:
+      - veza-network
+
   web-blue:
     build:
       context: ./apps/web