From c94fa0d23091b0d6542fa54bf59a054265fb86fa Mon Sep 17 00:00:00 2001
From: Samuel Berthe <dev@samuel-berthe.fr>
Date: Mon, 16 Mar 2026 03:28:06 +0100
Subject: [PATCH] fix: add division-by-zero guards and improve quoting in
 memcached rules (#512)

- Add `and memcached_max_connections > 0` to connection limit queries
- Add `and memcached_limit_bytes > 0` to memory usage query
- Switch hit-rate query to single quotes for cleaner PromQL readability
---
 _data/rules.yml | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/_data/rules.yml b/_data/rules.yml
index 898e2fc..93d39c8 100644
--- a/_data/rules.yml
+++ b/_data/rules.yml
@@ -1068,12 +1068,12 @@ groups:
                   1m delay allows a restart without triggering an alert.
               - name: Memcached connection limit approaching (> 80%)
                 description: "Memcached connection usage is above 80% on {{ $labels.instance }} (current value: {{ $value }}%)"
-                query: "(memcached_current_connections / memcached_max_connections * 100) > 80"
+                query: "(memcached_current_connections / memcached_max_connections * 100) > 80 and memcached_max_connections > 0"
                 severity: warning
                 for: 2m
               - name: Memcached connection limit approaching (> 95%)
                 description: "Memcached connection usage is above 95% on {{ $labels.instance }} (current value: {{ $value }}%)"
-                query: "(memcached_current_connections / memcached_max_connections * 100) > 95"
+                query: "(memcached_current_connections / memcached_max_connections * 100) > 95 and memcached_max_connections > 0"
                 severity: critical
                 for: 2m
               - name: Memcached out of memory errors
@@ -1083,7 +1083,7 @@ groups:
                 for: 5m
               - name: Memcached memory usage high (> 90%)
                 description: "Memcached memory usage is above 90% on {{ $labels.instance }} (current value: {{ $value }}%)"
-                query: "(memcached_current_bytes / memcached_limit_bytes * 100) > 90"
+                query: "(memcached_current_bytes / memcached_limit_bytes * 100) > 90 and memcached_limit_bytes > 0"
                 severity: warning
                 for: 5m
                 comments: |
@@ -1097,7 +1097,7 @@ groups:
                   A sustained eviction rate indicates memory pressure. Consider increasing memcached memory limit or reducing cache usage. Threshold of 10 evictions/s is a rough default — adjust based on your workload.
               - name: Memcached low cache hit rate (< 80%)
                 description: "Memcached cache hit rate is below 80% on {{ $labels.instance }} (current value: {{ $value }}%)"
-                query: "(rate(memcached_commands_total{command=\"get\", status=\"hit\"}[5m]) / (rate(memcached_commands_total{command=\"get\", status=\"hit\"}[5m]) + rate(memcached_commands_total{command=\"get\", status=\"miss\"}[5m])) * 100) < 80 and (rate(memcached_commands_total{command=\"get\", status=\"hit\"}[5m]) + rate(memcached_commands_total{command=\"get\", status=\"miss\"}[5m])) > 0"
+                query: '(rate(memcached_commands_total{command="get", status="hit"}[5m]) / (rate(memcached_commands_total{command="get", status="hit"}[5m]) + rate(memcached_commands_total{command="get", status="miss"}[5m])) * 100) < 80 and (rate(memcached_commands_total{command="get", status="hit"}[5m]) + rate(memcached_commands_total{command="get", status="miss"}[5m])) > 0'
                 severity: warning
                 for: 10m
                 comments: |