feat(RDS): create RDSLowDiskSpaceCount to display instances with less than 80% disk space

charts/prometheus-rds-alerts/prometheus_tests/RDSLowDiskSpaceCount.yml

@@ -0,0 +1,26 @@
+rule_files:
+    - rules.yml
+
+evaluation_interval: 1m
+
+tests:
+
+    - name: RDSLowDiskSpaceCount
+      interval: 1m
+      input_series:
+          - series: 'rds_free_storage_bytes{aws_account_id="111111111111",aws_region="eu-west-3",dbidentifier="db1"}'
+            values: '3221225472x10'  # 3GB
+          - series: 'rds_allocated_storage_bytes{aws_account_id="111111111111",aws_region="eu-west-3",dbidentifier="db1"}'
+            values: '21474836480x15'  # 20GB
+      alert_rule_test:
+          - alertname: RDSLowDiskSpaceCount
+            eval_time: 15m
+            exp_alerts:
+                - exp_labels:
+                      aws_account_id: 111111111111
+                      aws_region: eu-west-3
+                      severity: warning
+                  exp_annotations:
+                      description: "One or more RDS instances has <20% free disk space"
+                      summary: "Less than 20% free disk space on at least one instance"
+                      runbook_url: "https://qonto.github.io/database-monitoring-framework/0.0.0/runbooks/rds/RDSLowDiskSpaceCount"

charts/prometheus-rds-alerts/values.yaml

@@ -38,6 +38,15 @@ rules:
       summary: "{{ $labels.instance }} is reporting errors"
       description: "{{ $labels.instance }} is reporting {{ $value }} errors per minute"
 
+  RDSLowDiskSpaceCount:
+    expr: count(10 < max by (aws_account_id, aws_region, dbidentifier) (rds_free_storage_bytes{} * 100 / rds_allocated_storage_bytes{}) < 20) by (aws_account_id,aws_region) >= 1
+    for: 15m
+    labels:
+      severity: warning
+    annotations:
+      summary: "Less than 20% free disk space on at least one instance"
+      description: 'One or more RDS instances has <20% free disk space'
+
   RDSDiskSpaceLimit:
     expr: max by (aws_account_id, aws_region, dbidentifier) (rds_free_storage_bytes{} * 100 / rds_allocated_storage_bytes{}) < 10
     for: 15m

content/runbooks/rds/RDSLowDiskSpaceCount.md

@@ -0,0 +1,23 @@
+---
+title: Free disk space is under 20 percent for at least one instance
+---
+
+# RDSLowDiskSpaceCount
+
+## Meaning
+
+Alert is triggered when at least one RDS instance is under the threshold on storage left.
+
+## Impact
+
+The PostgreSQL instance(s) might stop to prevent data corruption if no more disk space is available.
+
+## Diagnosis
+
+1. Find affected instance list in prometheus with:
+
+   ```promql
+   max by (aws_account_id, aws_region, dbidentifier) (rds_free_storage_bytes{} * 100 / rds_allocated_storage_bytes{}) < 20
+   ```
+
+1. Refer to [RDSDiskSpaceLimit](RDSDiskSpaceLimit.md) for each of them as it's the same alert just ringing a bit earlier.