http-poller plugin add_field doesn't work #6773

[jsvd]

migrated from elastic/logstash#6773

---

When using 'add_field' in the http_poller input plugin of a Logstash configuration, the field is lost when the plugin returns an error on the test URL.

See example input block below. The Links LINK_1 and LINK_3 for example may return a success (http 200) and the added field 'environment' will be part of the resulting document.
But in a case were LINK_2_DOWN and LINK_3_UNREACHABLE return an error response (http <> 200) then the added field 'environment' is NOT part of the result document.

• Version: 2.4.x, 5.x
• Operating System: Linux
• Config File: (input block of the Logstash configuration file)
  input {
  # ITT Polling.
  http_poller {
  urls => {
  LINK_1 => "http://xxx-it.html"
  LINK_2_DOWN => "http://xxx-down.html"
  }
  request_timeout => 10
  interval => 300
  codec => plain
  metadata_target => "http_poller_metadata"
  add_field => { "environment" => "I" }
  }
  # UAT Polling.
  http_poller {
  urls => {
  LINK_3 => "http://xxx-uat.html"
  LINK_4_UNREACHABLE => "http://xxx-unreachable.html"
  }
  request_timeout => 10
  interval => 300
  codec => plain
  metadata_target => "http_poller_metadata"
  add_field => { "environment" => "A" }
  }
  }

[Benny-Git]

I just wanted to open a similar Issue and found this existing one.
I hit this issue with Logstash 6.6 this weekend, when our Healthcheck failed with a timeout, and then didn't include the metadata I needed.
I will try to include the add_field in a mutate filter as a workaround for now.