Logstash sprintf formatting for elasticsearch output plugin does not seem to resolve

[houdinisparks (yan yee wong)]

I am having trouble using sprintf to reference the event fields in the elasticsearch output plugin and I'm not sure why. Below is the event received from Filebeat and sent to Elasticsearch after filtering is complete:

    {
              "beat" => {
            "hostname" => "ca86fed16953",
                "name" => "ca86fed16953",
             "version" => "6.5.1"
        },
        "@timestamp" => 2018-12-02T05:13:21.879Z,
              "host" => {
            "name" => "ca86fed16953"
        },
              "tags" => [
            [0] "beats_input_codec_plain_applied",
            [1] "_grokparsefailure"
        ],
            "fields" => {
            "env" => "DEV"
        },
            "source" => "/usr/share/filebeat/dockerlogs/logstash_DEV.log",
          "@version" => "1",
        "prospector" => {
            "type" => "log"
        },
            "bgp_id" => "42313900",
           "message" => "{<some message here>}",
            "offset" => 1440990627,
             "input" => {
            "type" => "log"
        },
            "docker" => {
            "container" => {
                "id" => "logstash_DEV.log"
            }
        }
    }

I am trying to index the files this based on filebeat's environment. Here is my config file:

input {
  http { }
  beats {
    port => 5044
  }
}

filter {
  grok {
    patterns_dir => ["/usr/share/logstash/pipeline/patterns"]
    break_on_match => false
    match => { "message" => ["%{RUBY_LOGGER}"]
             }
  }
}

output {
  elasticsearch {
    hosts => ["elasticsearch:9200"]
    index => "%{[fields][env]}-%{+yyyy.MM.dd}"
  }
  stdout { codec => rubydebug }
}

I would think the referenced event fields would have already been populated by the time it reaches the elasticsearch output plugin. However, on the kibana end, it doesnt not register the formatted index. Instead, its since like this:

What have I done wrong?

[Christian_Dahlqvist]

Index names must be lowercased, so I believe you will need to lowercase the fields.env field if you want to use it. If you look in Kibana I suspect you will find that the data in the index you found actually might be coming from the http input and does not have the fields.env field set.