Add alerting rules

services/monitoring/prometheus.nix

@@ -67,14 +67,38 @@
                 annotations:
                   summary: "High CPU load on {{ $labels.instance }}"
                   description: "CPU load is high on {{ $labels.instance }}. Please check."
+              - alert: low_memory
+                expr: node_memory_MemAvailable_bytes / node_memory_MemTotal_bytes * 100 < 10
+                for: 2m
+                labels:
+                  severity: warning
+                annotations:
+                  summary: Low available memory on {{ $labels.instance }}
+                  description: Node memory is filling up (< 10% left)\n  VALUE = {{ $value }}
+              - alert: oom_kill
+                expr: increase(node_vmstat_oom_kill[1m]) > 0
+                for: 0m
+                labels:
+                  severity: warning
+                annotations:
+                  summary: Host OOM kill detected on {{ $labels.instance }}
+                  description: OOM kill detected
               - alert: nixos_upgrade_failed
                 expr: node_systemd_unit_state{name="nixos-upgrade.service", state="failed"} == 1
-                for: 1m
+                for: 0m
                 labels:
                   severity: critical
                 annotations:
                   summary: "NixOS upgrade failed on {{ $labels.instance }}"
                   description: "NixOS upgrade failed on {{ $labels.instance }}"
+              - alert: promtail_not_running
+                expr: node_systemd_unit_state{name="promtail.service", state="active"} == 0
+                for: 5m
+                labels:
+                  severity: warning
+                annotations:
+                  summary: "Promtail service not running on {{ $labels.instance }}"
+                  description: "The promtail service has not been active on {{ $labels.instance }} for 5 minutes."
           - name: nameserver_rules
             rules:
               - alert: unbound_down
@@ -105,7 +129,7 @@
                   description: "Caddy has been down on {{ $labels.instance }} more than 5 minutes."
           - name: nats_rules
             rules:
-              - alert: nats down
+              - alert: nats_down
                 expr: node_systemd_unit_state {instance="nats1.home.2rjus.net:9100", name = "nats.service", state = "active"} == 0
                 for: 5m
                 labels:
@@ -115,7 +139,7 @@
                   description: "NATS has been down on {{ $labels.instance }} more than 5 minutes."
           - name: nix_cache_rules
             rules:
-              - alert: build-flakes service failed
+              - alert: build-flakes_service_failed
                 expr: node_systemd_unit_state{instance="nix-cache01.home.2rjus.net:9100", name="build-flakes.service",state="failed"} == 1
                 for: 5m
                 labels: