Adding custom header in HTTP request of prometheus

Question

Prometheus send HTTP request to get monitor values. My custom export supports variety of clients (to monitors system status). There is a general REST API to get list of monitors:

/api/v1/monitor/find

the output result depend on Accept attribute in header. The default accept value is application/json.

I add new mime type to support prometheus (e.g. application/prometheus) into the API.

But, how to config Prometheus to add a custom header (Accept: application/prometheus)?

I know, it is possible to set param. But I`m looking for header. — Mostafa Barmshory, Jun 05 '17 at 12:43
maybe see also https://stackoverflow.com/questions/66032498/prometheus-scrape-metric-with-custom-header — David, Oct 01 '21 at 18:51

score 0 · Answer 1 · answered Jun 05 '17 at 12:58

Prometheus doesn't support setting headers, as that would lead to users creating hard to debug endpoints. You can either use a separate endpoint or pass a parameter.

Prometheus also already has a specified mime type for scrapes, so you could use that. See https://prometheus.io/docs/instrumenting/exposition_formats/

score 0 · Accepted Answer · edited Oct 31 '22 at 15:39

Actually it is not support in current version (V2.0 alpha).

If you take a look at the scrapes.go in the master branch, then you can see some constant header attached into request:

req.Header.Add("Accept", acceptHeader)
req.Header.Set("User-Agent", userAgentHeader)
req.Header.Set("X-Prometheus-Scrape-Timeout-Seconds", fmt.Sprintf("%f", s.timeout.Seconds()))

So, there are some basic mime-types which you can support:

application/vnd.google.protobuf;proto=io.prometheus.client.MetricFamily;encoding=delimited;q=0.7,text/plain;version=0.0.4;q=0.3,*/*;q=0.1

None of artifacts on premetheus.io added this header, so you have to build from source (master branch).

I run a PHP exporter (my own exporter), here is screen shot of request header

Adding custom header in HTTP request of prometheus

2 Answers2

Linked