Probe success rule (#45)

* probe failure rule

* build deps

* fmt

* follow naming patterns

* cleaner alert

* fix description

* warning rule

---------

Signed-off-by: Dylan Stephano-Shachter <dylan.stephano-shachter@canonical.com>
Co-authored-by: Luca Bello <36242061+lucabello@users.noreply.github.com>

src/prometheus_alert_rules/probe_failure.rule

@@ -0,0 +1,23 @@
+groups:
+  - name: probes
+    rules:
+    - alert: ProbeFailedOnce
+      expr: probe_success{} < 1
+      for: 0m
+      labels:
+        severity: warning
+      annotations:
+        summary: Blackbox Exporter target {{ $labels.probe_target }} has failed.
+        description: >
+          Blackbox Exporter target {{ $labels.probe_target }} has failed.
+          LABELS = {{ $labels }}
+    - alert: ProbeFailed
+      expr: probe_success{} < 1
+      for: 5m
+      labels:
+        severity: critical
+      annotations:
+        summary: Blackbox Exporter target {{ $labels.probe_target }} has failed for the last five minutes.
+        description: >
+          Blackbox Exporter target {{ $labels.probe_target }} has failed for the last five minutes.
+          LABELS = {{ $labels }}