Fixing Missing Metrics and Scrape Failures in Prometheus

Details: Category: Troubleshooting Tips; By Mindful Chase; 09.Feb; Hits: 31

Prometheus users sometimes encounter an issue where metrics appear missing or are not being scraped correctly, leading to incomplete dashboards, missing alerts, and unreliable monitoring. This problem, known as the 'Prometheus Missing Metrics Issue,' occurs due to incorrect scrape configurations, target misconfigurations, or relabeling rules inadvertently dropping metrics.

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Understanding Missing Metrics in Prometheus

Prometheus scrapes metrics from targets at regular intervals, but incorrect configurations, network issues, or time synchronization problems can cause certain metrics to disappear or never be collected.

Common Causes of Missing Metrics

Incorrect scrape interval or timeout: Metrics are missed due to long scrape durations.
Target endpoints unreachable: Firewalls, DNS issues, or misconfigured exporters prevent scraping.
Improper relabeling rules: Metrics may be dropped or incorrectly filtered out.
Prometheus storage retention limits: Older metrics may be deleted before retrieval.

Diagnosing Missing Metrics

Checking Scrape Targets

Verify which targets are being scraped:

curl -s http://localhost:9090/api/v1/targets | jq

Ensure targets are in the UP state.

Inspecting Prometheus Logs

Enable debug logging:

prometheus --log.level=debug

Verifying Metric Availability

Manually query Prometheus for missing metrics:

curl -s http://localhost:9090/api/v1/query?query=my_metric_name

Fixing Missing Metrics Issues

Adjusting Scrape Configuration

Ensure proper scrape interval and timeout:

scrape_configs:
  - job_name: "my_app"
    scrape_interval: 15s
    scrape_timeout: 10s

Debugging Relabeling Rules

Check if metrics are being dropped:

relabel_configs:
  - source_labels: ["job"]
    regex: "unwanted.*"
    action: drop

Ensure important metrics are not unintentionally filtered.

Fixing Exporter and Target Connectivity

Test metric endpoints manually:

curl -s http://my_exporter:9100/metrics

Ensure firewall rules allow Prometheus to reach targets.

Increasing Storage Retention

Adjust Prometheus retention settings:

--storage.tsdb.retention.time=30d

Preventing Future Metric Loss

Monitor scrape targets using the up metric.
Use proper relabeling to avoid unintentionally filtering required metrics.
Ensure exporters and targets remain consistently available.

Conclusion

Prometheus missing metrics can lead to incomplete monitoring and unreliable alerts. By checking scrape configurations, debugging relabeling rules, and ensuring target connectivity, developers can ensure consistent and accurate metric collection.

FAQs

1. Why is Prometheus not collecting my metrics?

Potential causes include incorrect scrape configurations, target unavailability, or relabeling filters.

2. How can I check if my target is being scraped?

Use curl -s http://localhost:9090/api/v1/targets to verify target status.

3. Can relabeling rules accidentally remove metrics?

Yes, improperly configured drop actions can filter out required metrics.

4. How do I increase Prometheus metric retention?

Adjust --storage.tsdb.retention.time to a higher value.

5. How do I ensure my exporters are working?

Manually test their endpoints with curl to confirm metric exposure.

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