The output for version flag is printed on stderr

[nkn1111]

Was facing an issue with the version check for the exporter. But found a similar issue on node_exporter issues which is already fixed. Linking the same here prometheus/node_exporter#1271

Can we do the same fix here?

Host operating system: Linux 3.10.0-1062.12.1.el7.x86_64 #1 SMP Tue Feb 4 23:02:59 UTC 2020 x86_64 x86_64 x86_64 GNU/Linux

blackbox_exporter version: blackbox_exporter, version 0.20.0 (branch: HEAD, revision: 91372eb)

What is the blackbox.yml module config.

What is the prometheus.yml scrape config.

What logging output did you get from adding &debug=true to the probe URL?

What did you do that produced an error?

Register the version output via ansible and display it using debug.
"cmd": [
"/usr/local/bin/blackbox_exporter",
"--version"
]

What did you expect to see?

"stdout": "blackbox_exporter, version 0.20.0

What did you see instead?

"stderr": "blackbox_exporter, version 0.20.0

[mem]

There's a relatively straightforward "fix" for this:

kingpin.CommandLine.UsageWriter(os.Stdout)

But it's worth nothing that this is NOT what Prometheus (or promtool, etc) does.

Looking thru the discussion in the other issue, it was changed to accommodate this request, even if the specific issue being reported is fixed by:

"cmd": [ "sh", "-c", "/usr/local/bin/blackbox_exporter --version 2>&1" ]
"cmd": [ "sh", "-c", "/usr/local/bin/blackbox_exporter", "--version", "2>&1" ]  // maybe this

(quoting might need to be different, not sure how ansible processes this)

[nkn1111]

Thank you. I might have found a workaround for my issue on ansible by adding multiple conditions to check both stdout and stderr. Since the Prometheus and other subsidiaries of Prometheus are showing the version output on stdout, It makes sense to have the same in here as well. Can you consider this improvement in a future release?

[roidelapluie]

Yes, are you willing to contribute this change to the project? Thanks!

[roidelapluie]

But it's worth nothing that this is NOT what Prometheus (or promtool, etc) does.

It was changed in Prometheus: prometheus/prometheus#8542 and per dev summit, we want it everywhere.

[nkn1111]

Hey! I missed this update. TBH I don't have prior knowledge in go lang. To save you some time, it's better for someone familiar with the exporter code to raise a PR. TIA.

[nkn1111]

Thank you so much @mem @roidelapluie