Reword Prometheus alert messages

Change-Id: I54e02e0741d53ec7b2335145dc968b7b8c8f5e00

linux/meta/prometheus.yml

 server:
   alert:
     AvgCPUUsageIdle:
-      if: avg_over_time(cpu_usage_idle{cpu="cpu-total"}[5m]) < {{ prometheus_server.get('alert', {}).get('AvgCPUUsageIdle', {}).get('var', {}).get('threshold', 10) }}
+      {%- set cpu_idle_threshold = prometheus_server.get('alert', {}).get('AvgCPUUsageIdle', {}).get('var', {}).get('threshold', 10) %}
+      if: avg_over_time(cpu_usage_idle{cpu="cpu-total"}[5m]) < {{ cpu_idle_threshold }}
       {% raw %}
       labels:
         severity: warning
         service: system
       annotations:
-        summary: 'Avarage CPU usage (idle) for node {{ $labels.host }} is low'
-        description: 'Avarage CPU usage (idle) for node {{ $labels.host }} is low {{ $value }}'
-      {% endraw %}
+        summary: 'Idle CPU usage too low on {{ $labels.host }}'
+        description: 'The average idle CPU usage is too low on node {{ $labels.host }} (current value={{ $value }}, threshold={% endraw %}{{ cpu_idle_threshold}})'
     PredictLinearDiskFree:
       if: 'predict_linear(disk_free[1h], 8*3600) < 0'
       {% raw %}
         severity: warning
         service: system
       annotations:
-        summary: 'Disk space ({{ $labels.path }}) is filling on {{ $labels.host }}'
-        description: 'Disk space ({{ $labels.path }}) will be full in 8h on {{ $labels.host }}'
+        summary: 'Free space for {{ $labels.path }} too low on {{ $labels.host }}'
+        description: 'The disk partition ({{ $labels.path }}) will be full in less than 8 hours on {{ $labels.host }}'
       {% endraw %}
     PredictLinearDiskInodesFree:
       if: 'predict_linear(disk_inodes_free[1h], 8*3600) < 0'
         severity: warning
         service: system
       annotations:
-        summary: 'Disk inodes ({{ $labels.path }}) are filling on {{ $labels.host }}'
-        description: 'Disk inodes ({{ $labels.path }}) will be full in 8h on {{ $labels.host }}'
+        summary: 'Free inodes for {{ $labels.path }} too low on {{ $labels.host }}'
+        description: 'The disk inodes ({{ $labels.path }}) will be full in less than 8 hours on {{ $labels.host }}'
       {% endraw %}
     AvgMemAvailablePercent:
-      if: avg_over_time(mem_available_percent[5m]) < {{ prometheus_server.get('alert', {}).get('AvgMemAvailablePercent', {}).get('var', {}).get('threshold', 10) }}
+      {%- set mem_avail_threshold = prometheus_server.get('alert', {}).get('AvgMemAvailablePercent', {}).get('var', {}).get('threshold', 10) %}
+      if: avg_over_time(mem_available_percent[5m]) < {{ mem_avail_threshold }}
       {% raw %}
       labels:
         severity: warning
         service: system
       annotations:
-        summary: 'Free memory is low on {{ $labels.host }}'
-        description: 'Free memory percent for node {{ $labels.host }} is low {{ $value }}'
-      {% endraw %}
+        summary: 'Free memory too low on {{ $labels.host }}'
+        description: 'The percentage of free memory is too low on node {{ $labels.host }} (current value={{ $value }}, threshold={% endraw %}{{ mem_avail_threshold }})'
     SystemLoad5:
       if: system_load5 / system_n_cpus > {{ prometheus_server.get('alert', {}).get('SystemLoad5', {}).get('var', {}).get('threshold', 3) }}
       {% raw %}