logstash _grokparsefailure for realy simple tag

Question

I don't understand why I have a grokparse failure for this simple config :

input {
  file {
    path => "/var/log/*.log"
    codec => json {
    }
  }
}
filter {
  grok {
    add_tag => ["test"]
  }
}
output {
  elasticsearch {
      /.../
  }
}

The logs are correcly sent to elasticsearch, the json is correcly parsed, but the added tag don't work, instead I have a tag "_grokparsefailure". What I want is to pass a static value as a tag.

I am surely missing something dumb, but I can't find what.

Answer 1

Your grok filter does nothing, there is no pattern to match, the tag would only be applied after a successful match.

To add a tag in your case you can use the tags option in your input or the mutate filter.

To use the tags option just add change your input to this one:

input {
  file {
    path => "/var/log/*.log"
    codec => json
    tags => ["test"] 
  }
}

To use the mutate filter, put the bellow config inside your filter block.

mutate {
    add_tag => ["test"]
} 

Both configurations will add a test tag to all your messages.