VMAgent can't scrape application without header: Accept: text/plain

[to4kin]

Describe the bug
One of my springboot applications return metrics only if the correct header set:

curl -v localhost:9080/actuator/prometheus

* Connected to localhost (::1) port 9080 (#0)
> GET /actuator/prometheus HTTP/1.1
> Host: localhost:9080
> User-Agent: curl/7.64.0
> Accept: */*
>
< HTTP/1.1 406
< Content-Length: 0
< Date: Tue, 07 Jul 2020 15:55:26 GMT
<
* Connection #0 to host localhost left intact

curl -v -H "Accept: text/plain" localhost:9080/actuator/prometheus

* Connected to localhost (::1) port 9080 (#0)
> GET /actuator/prometheus HTTP/1.1
> Host: localhost:9080
> User-Agent: curl/7.64.0
> Accept: text/plain
>
< HTTP/1.1 200
< Content-Type: text/plain; version=0.0.4;charset=utf-8
< Content-Length: 17870
< Vary: Accept-Encoding
< Date: Tue, 07 Jul 2020 15:56:28 GMT
<

curl http://vmagent-host:8429/targets

state=down, endpoint=http://<IP:PORT>/actuator/prometheus, labels={application="NAME", instance="INSTANCE-NAME", job="JOB-NAME"}, last_scrape=24.894s ago, scrape_duration=0.005s, error="unexpected status code returned when scraping \"http://<IP:PORT>/actuator/prometheus\": 406; expecting 200; response body: \"\""

VMAgent cannot scrape these metrics when prometheus can

To Reproduce
Same issue in Prometheus: prometheus/client_java#267

Expected behavior
VMAgent should scrape this application too

Version
The line returned when passing --version command line flag to binary. For example:

$ ./victoria-metrics-prod --version
vmagent-20200702-100247-tags-v1.37.4-cluster-0-g0f754bea4

Used command-line flags
/vmagent-prod -remoteWrite.url=http://victoria-metrics-vminsert:8480/insert/0/prometheus/ -promscrape.consulSDCheckInterval=30s -promscrape.suppressScrapeErrors -promscrape.config=/vmagent-remotewrite-data/scrape.yml

[valyala]

@to4kin , the issue should be fixed in the commit 87f8c72 . Could you build vmagent from this commit according to these docs and verify whether it now properly scrapes Spring Boot servers?

[valyala]

@to4kin , the bugfix has been included in v1.38.0 release. Closing the issue as fixed. Feel free re-opening if v1.38.0 or newer release of vmagent doesn't work as expected for your case.