I have a Quarkus project (v3.8.1), with the extensions quarkus-micrometer and quarkus-micrometer-registry-prometheus. My problem is that when calling the metrics endpoint from Postman, I get a 200 OK, but when the endpoint is scraped from the Prometheus server, I get a 406 Not Acceptable response.

This is my config in the application.yml :

quarkus:
  micrometer:
    enabled: true
    export:
      prometheus:
        enabled: true
        path: metrics/prometheus

My prometheus.yml config :

global:
  scrape_interval:     15s
  evaluation_interval: 15s
scrape_configs:
  - job_name: 'prometheus'
    static_configs:
      - targets: ['localhost:9090']

  - job_name: 'quarkus-micrometer'
    metrics_path: '/q/metrics/prometheus'
    scrape_interval: 3s
    static_configs:
      - targets: ['MY_IP:8080']

I tried comparing the two requests, and I found that the request coming from the Prometheus server scraping contains Accept headers, and this is the headers with “application/openmetrics-text;…” that are responsible from the 406.

Example request from Prometheus server scraping :

date INFO  [io.qua.htt.access-log] (vert.x-eventloop-thread-2) 
GET /q/metrics/prometheus HTTP/1.1
Accept: application/openmetrics-text;version=1.0.0;q=0.5
Accept: application/openmetrics-text;version=0.0.1;q=0.4
Accept: text/plain;version=0.0.4;q=0.3
Accept: */*;q=0.2
User-Agent: Prometheus/2.52.0
Host: MY_IP:8080
Accept-Encoding: gzip
X-Prometheus-Scrape-Timeout-Seconds: 3

Example request from Postman :

date INFO  [io.qua.htt.access-log] (vert.x-worker-thread-1) 
GET /q/metrics/prometheus HTTP/1.1
User-Agent: PostmanRuntime/7.37.3
Host: MY_IP:8080
Postman-Token: 1509bc27-58ed-498f-9d74-73ee5348eb97
Accept-Encoding: gzip
Accept-Encoding:  deflate
Accept-Encoding:  br

I expect finding a solution for having 200 OK response on the endpoint /q/metrics/prometheus, even with the Accept header application/openmetrics-text, or find a way to not send that header from the Prometheus server.