Describe the bug

Prometheus 3.0 is now rejecting goss /healthz endpoint responses

Workaround

In the prometheus scrape configuration documented at https://prometheus.io/docs/prometheus/latest/configuration/configuration/#scrape_config, specify the fallbackScrapeProtocol: PrometheusText0.0.4

How To Reproduce

goss --gossfile goss-integration.yaml serve --listen-addr :8080 --format prometheus

Expected Behavior

Prometheus accepts goss http responses without error.

Actual Behavior

The UI displays

Error scraping target: received unsupported Content-Type "application/vnd.goss-prometheus" and no fallback_scrape_protocol specified for target

The prometheus logs include the following error

time=2025-01-02T13:45:26.208Z level=ERROR source=scrape.go:1585 msg="Failed to determine correct type of scrape target." component="scrape manager" scrape_pool=podMonitor/intranet-proxy/goss-pod-monitor/0 target=http://10.42.13.15:8080/healthz content_type=application/vnd.goss-prometheus fallback_media_type="" err="received unsupported Content-Type \"application/vnd.goss-prometheus\" and no fallback_scrape_protocol specified for target"

Environment:

• Version of goss: goss version v0.4.9
• OS/Distribution version (if applicable)

References

https://prometheus.io/docs/prometheus/latest/migration/#scrape-protocols

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.

If a scrape target is not providing the correct Content-Type header the fallback protocol can be specified using the fallback_scrape_protocol parameter.
This is a breaking change as scrapes that may have succeeded with Prometheus v2 may now fail if this fallback protocol is not specified.

https://prometheus.io/docs/instrumenting/exposition_formats/#text-based-format
Basic info

HTTP Content-Type text/plain; version=0.0.4 (A missing version value will lead to a fall-back to the most recent text format version.)