Working on Blackbox's "fail_if_body_not_matches_regexp".

[yagyans...@gmail.com]

Hi. I am using blackbox_exporter version 0.18.0 and I am using http prober to check if the response by my URL is "OK" or not. Below is the configuration of the module.

  http_healthcheck_ok:
    prober: http
    timeout: 10s
    http:
      valid_http_versions: ["HTTP/1.1", "HTTP/2.0", "HTTP/1.0"]
      fail_if_body_not_matches_regexp: ['OK']
      method: GET
      no_follow_redirects: false
      fail_if_ssl: false
      fail_if_not_ssl: false
      tls_config:
        insecure_skip_verify: true
      preferred_ip_protocol: "ip4"

So, whenever my URL throws anything other than OK in the response body, probe_failed_due_to_regex should 1 right? But when the URL was throwing NOK as the response body, probe_failed_due_to_regex was still 0, whereas it should be 1. Am I missing something here?

Thanks in advance!

[yagyans...@gmail.com]

Can someone please help! I am confused here.

[Julius Volz]

Hi,

the Blackbox exporter doesn't do full-string matching for these regexes, but substring matching, so it also matches if the body contains "OK" anywhere (which is true for "NOK"). Try '^OK$` instead?

Also, in case your HTTP endpoint returns a status code other than 2xx, you will have to set the "valid_status_codes" list to the allowed ones (it defaults to 2xx).

Regards,

Julius

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Julius Volz

PromLabs - promlabs.com

[Yagyansh S. Kumar]

Thanks, Julius.

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Thanks & Regards

Yagyansh S. Kumar

DevOps Engineer, Dailyhunt - Bangalore

8696078312,8209496395

[Yagyansh S. Kumar]

Hi Julius,

Using the expression "^OK$" leads to the failure of all the checks for which response was OK. This seems weird to me. Ideally, should have worked. Any more workarounds or suggestions to achieve this?

[Marcelo Magallón]

blackbox_exporter applies the provided regular expression against the entire body.

This means in particular that if your body is something like ['O', 'K', '\n'] (O, followed by K, followed by a carriage return), the regular expression '^OK$' WILL NOT match because '$' anchors it to the end of the body, not the end of the line.

In order to match lines, not the whole body, you have to write '(?m:^OK$)'. This will match 'OK' on a line by its own, but not say NOK on a line by its own. It will also match on a body like 'Something\nOK\nsomething\n'.

I hope this helps,

Marcelo

To view this discussion on the web visit https://groups.google.com/d/msgid/prometheus-users/CAFGi5vArLJ1m-2Huui6P50N6HFdwztTDw7m0-bC8fGhiV9q0fg%40mail.gmail.com.

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Marcelo Magallón

[Julius Volz]

Thanks for clarifying, Marcelo! Having never used the regex matching myself, I also wasn't 100% sure about that :)

[Yagyansh S. Kumar]

Thanks, Marcelo.