Hands-On Infrastructure Monitoring with Prometheus

From logs to metrics

In a perfect world, all applications and services would have been properly instrumented and we would only be required to collect metrics to gain visibility. External exporters are a stop-gap approach that simplifies our work, but not every service exposes its internal state through a neat API. Older daemon software, such as Postfix or ntpd, makes use of logging to relay their inner workings. For these cases, we're left with two options: either instrument the service ourselves (which isn't possible for closed source software) or rely on logs to gather the metrics we require. The next topics go over the available options for extracting metrics from logs.