Cassandra mixin updates .lint and alerts with better filtering on metrics (#1173)

Author: StefanKurek

apache-cassandra-mixin/.lint

@@ -17,6 +17,8 @@ exclusions:
       - panel: "Keyspaces count"
       - panel: "Repair jobs started"
       - panel: "Repair jobs completed"
+  panel-datasource-rule:
+    reason: "Loki datasource variable is being named as loki_datasource now while linter expects 'datasource'"
   template-datasource-rule:
     reason: "Based on new convention we are using variable names prometheus_datasource and loki_datasource where as linter expects 'datasource'"
   template-instance-rule:

apache-cassandra-mixin/alerts/alerts.libsonnet

@@ -115,7 +115,7 @@
           {
             alert: 'HighCpuUsage',
             expr: |||
-              jvm_process_cpu_load * 100 > %(alertsCriticalHighCpuUsage5m)s
+              jvm_process_cpu_load{job=~"integrations/apache-cassandra"} * 100 > %(alertsCriticalHighCpuUsage5m)s
             ||| % $._config,
             'for': '5m',
             labels: {
@@ -133,7 +133,7 @@
           {
             alert: 'HighMemoryUsage',
             expr: |||
-              sum(jvm_memory_usage_used_bytes{area="Heap"}) / sum(jvm_physical_memory_size) * 100 > %(alertsCriticalHighMemoryUsage5m)s
+              sum(jvm_memory_usage_used_bytes{job=~"integrations/apache-cassandra", area="Heap"}) / sum(jvm_physical_memory_size{job=~"integrations/apache-cassandra"}) * 100 > %(alertsCriticalHighMemoryUsage5m)s
             ||| % $._config,
             'for': '5m',
             labels: {