prometheus: add some alerts

hosts/prometheus/default.nix

@@ -61,6 +61,57 @@
                 severity: error
               annotations:
                 summary: service gets oom killed
+            - alert: disk_free
+              expr: collectd_df_df_complex{type="free"} < 1024*1024*1024
+              for: 10m
+              labels:
+                severity: warn
+              annotations:
+                summary: filesystem has less than 1GB of free space
+            - alert: load1
+              expr: node_load1 > 100
+              for: 1m
+              labels:
+                severity: warn
+              annotations:
+                summary: high loadavg
+            - alert: systemd_unit_failed
+              expr: node_systemd_unit_state{state="failed"} > 0
+              for: 10m
+              labels:
+                severity: error
+              annotations:
+                summary: failed systemd units
+          - name: network
+            rules:
+            - alert: load1
+              expr: collectd_load_0 > 4
+              for: 1m
+              labels:
+                severity: warn
+              annotations:
+                summary: high loadavg
+            - alert: memory_free
+              expr: collectd_memory{memory="free"} < 4*1024*1024
+              for: 10m
+              labels:
+                severity: warn
+              annotations:
+                summary: memory full
+            - alert: throughput0
+              expr: increase(collectd_interface_if_octets_0_total[10m]) > 600 * 60 * 1024 * 1024
+              for: 2h
+              labels:
+                severity: warn
+              annotations:
+                summary: sustained throughput
+            - alert: throughput1
+              expr: increase(collectd_interface_if_octets_1_total[10m]) > 600 * 60 * 1024 * 1024
+              for: 2h
+              labels:
+                severity: warn
+              annotations:
+                summary: sustained throughput
       ''
     ];