Content-Type header for Prometheus 3.0.0

[jcpunk]

Use Case

Prometheus 3.0.0 has the option (by default) to be far more strict about what content it scrapes. This can cause unexpected scrape failures for the prometheus exporter.

Expected behavior

Set the header "to the correct value".

Actual behavior

Header unset

Additional info

From : https://prometheus.io/docs/prometheus/3.0/migration/

Prometheus v3 is more strict concerning the Content-Type header received when scraping. Prometheus v2 would default to the standard Prometheus text protocol if the target being scraped did not specify a Content-Type header or if the header was unparsable or unrecognised. This could lead to incorrect data being parsed in the scrape. Prometheus v3 will now fail the scrape in such cases.