如何在Prometheus告警描述中将剩余过期秒数转为天数？

Prometheus alert templates don't support direct arithmetic operations (like division) on the $value variable within the template syntax—this is why your previous attempts to divide $value by 86400 failed. Instead, you need to compute remaining days either in your alert's PromQL expression or via a recording rule.

Option 1: Adjust the Alert Expression to Return Days Directly #

Modify your alert rule's expression to calculate remaining days instead of seconds. This way, $value will already be in days when used in the annotation.

Example alert rule:

groups:
- name: ssl_cert_alerts
  rules:
  - alert: SSLCertExpiringIn29Days
    expr: (probe_ssl_last_chain_expiry_timestamp_seconds - time()) / 86400 < 29
    for: 5m
    annotations:
      description: "SSL certificate expires in {{ printf \"%.2f\" $value }} days"
      summary: "SSL certificate expiring soon for {{ $labels.instance }}"

• The expression (probe_ssl_last_chain_expiry_timestamp_seconds - time()) / 86400 converts remaining seconds to days by dividing by 86400 (seconds per day).
• printf "%.2f" $value formats the days to two decimal places for readability.

Option 2: Use a Recording Rule to Precompute Remaining Days #

If you need the remaining days metric for other queries or alerts, create a recording rule to precompute it once, then reference the new metric in your alert.

Step 1: Define the Recording Rule #

Add this to your Prometheus rules configuration:

groups:
- name: ssl_recording_rules
  rules:
  - record: probe_ssl_cert_remaining_days
    expr: (probe_ssl_last_chain_expiry_timestamp_seconds - time()) / 86400

Step 2: Create the Alert Using the Precomputed Metric #

groups:
- name: ssl_cert_alerts
  rules:
  - alert: SSLCertExpiringIn29Days
    expr: probe_ssl_cert_remaining_days < 29
    for: 5m
    annotations:
      description: "SSL certificate expires in {{ printf \"%.2f\" $value }} days"
      summary: "SSL certificate expiring soon for {{ $labels.instance }}"

Key Notes #

• Prometheus template functions are limited to formatting and label manipulation—all arithmetic must be handled in PromQL (either in the alert expression or recording rule).
• If you prefer a human-readable duration (e.g., "28d 4h 30m"), you can use the humanizeDuration function with the original seconds value:

  description: "SSL certificate expires in {{ humanizeDuration $value }}"
  

  This requires keeping the alert expression in seconds, as humanizeDuration expects a value in seconds.

内容的提问来源于stack exchange，提问作者Lino Kaiser