Prometheus example crashes

[bachittle]

Describe your environment Describe any aspect of your environment relevant to the problem, including your platform, build system, version numbers of installed dependencies, etc. If you're reporting a problem with a specific version of a library in this repo, please check whether the problem has been fixed on main branch.

• windows 10 x64
• ubuntu gcc x64

Steps to reproduce
Describe exactly how to reproduce the error. Include a code sample if applicable.

• run prometheus in docker container
• compile opentelemetry via cmake with the WITH_PROMETHEUS flag turned on
• run the prometheus_example

What is the expected behavior?
What did you expect to see?

• Connection to my prometheus docker service, with metrics pushed in

What is the actual behavior?
What did you see instead?

• program crashes, outputting: null context when constructing CivetServer. Possible problem binding to port.

[marcalff]

@bachittle

Thanks for the report.

Do you have a call stack by chance, this would help.

[bachittle]

PrometheusExporter example program running ...
./prometheus_example(_Z7handlerv+0x32) [0x55b5a3a715f4]
/lib/x86_64-linux-gnu/libstdc++.so.6(+0xae24c) [0x7f4d0a49724c]
/lib/x86_64-linux-gnu/libstdc++.so.6(+0xae2b7) [0x7f4d0a4972b7]
/lib/x86_64-linux-gnu/libstdc++.so.6(+0xae518) [0x7f4d0a497518]
./prometheus_example(_ZN11CivetServerC1ERKSt6vectorINSt7__cxx1112basic_stringIcSt11char_traitsIcESaIcEEESaIS6_EEPK14CivetCallbacksPKv+0x346) [0x55b5a3b30320]
./prometheus_example(_ZN10prometheus6detail11make_uniqueI11CivetServerJSt6vectorINSt7__cxx1112basic_stringIcSt11char_traitsIcESaIcEEESaIS9_EERPK14CivetCallbacksEEESt10unique_ptrIT_St14default_deleteISH_EEDpOT0_+0x5a) [0x55b5a3b2d2c8]
./prometheus_example(_ZN10prometheus7ExposerC1ESt6vectorINSt7__cxx1112basic_stringIcSt11char_traitsIcESaIcEEESaIS7_EEPK14CivetCallbacks+0x49) [0x55b5a3b2c765]
./prometheus_example(_ZN10prometheus7ExposerC2ERKNSt7__cxx1112basic_stringIcSt11char_traitsIcESaIcEEEmPK14CivetCallbacks+0x141) [0x55b5a3b2c5fb]
./prometheus_example(_ZN13opentelemetry2v18exporter7metrics18PrometheusExporterC2ERKNS2_25PrometheusExporterOptionsE+0xa8) [0x55b5a3b14580]
./prometheus_example(+0x2d5737) [0x55b5a3a71737]
./prometheus_example(main+0x134) [0x55b5a3a725eb]
/lib/x86_64-linux-gnu/libc.so.6(+0x29d90) [0x7f4d0a0e3d90]
/lib/x86_64-linux-gnu/libc.so.6(__libc_start_main+0x80) [0x7f4d0a0e3e40]
./prometheus_example(_start+0x25) [0x55b5a3a714f5]

The issue comes from the prometheus exporter. It uses civet server and, as the error states, generates a null context and throws at this part of the code:

[esigo]

Hi @bachittle,
Thanks for reaching out to us.
Is your port 8080 already used by some other process when you run into this issue?

[bachittle]

well that is what is being used by prometheus. Unless the address you specify in the url is what is used by another process (civet web server)? In that case how do you specify where the prometheus url is?

[esigo]

sorry I mentioned the wrong port. The default port for the example app is 9464. You could change the port with:
bazel run //examples/prometheus/... -- all localhost:<port>
or pass all localhost:<port> as arg to your executable. You then need to update the port in the yaml file.
Please make sure the port is not used by any other app.

[bachittle]

ok, so the documentation seems to be a bit confusing then in this regard. It says it will export data via the metrics_exporter::PrometheusExporterOptions::url, but in the code this is set to localhost:8080, not localhost:9464. Also, I tried running prometheus on port 9464 and it did not connect and show metrics results. Maybe I am just confused as to how it works, perhaps this documentation can also be fixed?

[lalitb]

Also, I tried running prometheus on port 9464 and it did not connect and show metrics results.

@bachittle - There are few changes in prometheus exporter recently in main branch (#1953), can you follow the example and see if you can fetch the metrics - https://github.com/open-telemetry/opentelemetry-cpp/blob/main/examples/prometheus/main.cc

Meanwhile, will go through the docs and modify the steps documented there.

[bachittle]

thank you, have been working on other things but glad this got fixed!