Prometheus is an open-source systems monitoring and alerting toolkit originally built at SoundCloud. It is now a standalone open-source project and maintained independently of any company. Prometheus collects and stores its metrics as time series data, i.e., metrics information is stored with the timestamp at which it was recorded, alongside optional key-value pairs called labels.
When using Prometheus, one common symptom that users may encounter is the throttling of alerts. This occurs when there are too many alerts being generated in a short period, overwhelming the system and potentially causing important alerts to be missed or delayed.
Users may notice that alerts are not being sent as expected, or that they are receiving a large volume of alerts in a short time frame, leading to alert fatigue and making it difficult to identify critical issues.
The root cause of alert throttling in Prometheus is often due to improperly configured alert thresholds or a lack of alert grouping. When too many alerts are triggered simultaneously, it can lead to a bottleneck in the alerting pipeline.
Prometheus uses Alertmanager to handle alerts. Alertmanager is responsible for deduplicating, grouping, and routing alerts to the correct receiver integrations such as email, PagerDuty, or Slack. When overwhelmed, Alertmanager may throttle alerts to manage the load.
To address the issue of throttling alerts, follow these steps:
Review your alerting rules to ensure that thresholds are set appropriately. Avoid setting thresholds too low, which can lead to frequent triggering of alerts. For example, if you have an alert for CPU usage, consider setting it to trigger only when usage exceeds 80% for a sustained period, rather than 50%.
groups:
- name: example
rules:
- alert: HighCPUUsage
expr: node_cpu_seconds_total{mode="idle"} < 20
for: 5m
labels:
severity: warning
annotations:
summary: "High CPU usage detected"
Use alert grouping in Alertmanager to reduce the number of alerts sent. Group alerts by common labels such as instance or job. This helps in consolidating alerts and reducing noise.
route:
group_by: ['alertname', 'job']
group_wait: 30s
group_interval: 5m
repeat_interval: 1h
receiver: 'team-X-pager'
Inhibition rules allow you to mute alerts based on the presence of other alerts. This can be useful to prevent alert storms when a root cause alert is already firing.
inhibit_rules:
- source_match:
severity: 'critical'
target_match:
severity: 'warning'
equal: ['alertname', 'cluster', 'service']
For more information on configuring alerts and managing Alertmanager, refer to the official Prometheus Alertmanager documentation. Additionally, the Prometheus Alerting Best Practices page offers valuable insights into effective alerting strategies.
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