Metrics derived from logs and correlation with Prometheus

14 min
Audience
beginner who has read lessons 01 to 03 of this module and module 2 (PromQL)
Duration
45 to 60 min
Module
5/7
Target skill
turn a log query into a curve (rate, count_over_time, sum by, bytes_rate, unwrap), compare figure by figure what Prometheus and Loki say about the same outage, and go from an HTTP header to the matching log line

In one picture

Ask the same question to two witnesses: "how many requests failed with 500 in the last five minutes?". Prometheus answers by looking at a counter the API keeps up to date and that it scrapes every 15 seconds; it estimates the slope between two scrapes. Loki answers by counting the log lines whose code label is 500; it scrapes nothing, it has every line. On the course machine, during an outage triggered with casser erreurs, both said:

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This lesson is part of the “Logs: Loki, Alloy and LogQL” module

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