Rules are defined separately from the main Prometheus configuration file, and are included by the latter through the rule_files top-level configuration key. They are evaluated periodically, and that interval can be defined globally with evaluation_interval inside global (defaults to one minute).
We can see this by looking at the configuration provided with the test environment:
vagrant@prometheus:~$ cat /etc/prometheus/prometheus.ymlglobal:... evaluation_interval: 1m...rule_files: - "recording_rules.yml"...
rule_files takes a list of paths, which can be relative to the main Prometheus configuration or absolute paths. Additionally, globs can be used to match filenames (not directories); for example, /etc/prometheus/rules/*.yml ...
