$ cat prometheus.yml
rule_files:
- recording.rules
$ cat recording.rules
groups:
  - name: example
    rules:
    - record: test
      expr: 1
$ prometheus
ts=2023-11-05T15:56:15.361Z caller=main.go:556 level=info msg="Starting Prometheus Server" mode=server version="(version=2.42.0, branch=non-git, revision=non-git)"
...

curl -v 'http://127.0.0.1:9090/federate?match[]=test'
*   Trying 127.0.0.1:9090...
* Connected to 127.0.0.1 (127.0.0.1) port 9090 (#0)
> GET /federate?match[]=test HTTP/1.1
> Host: 127.0.0.1:9090
> User-Agent: curl/7.88.1
> Accept: */*
>
< HTTP/1.1 200 OK
< Content-Type: text/plain; version=0.0.4; charset=utf-8
< Date: Sun, 05 Nov 2023 15:54:34 GMT
< Content-Length: 54
<
# TYPE test untyped
test{instance=""} 1 1699199580857
* Connection #0 to host 127.0.0.1 left intact