Logstash worker dies with no reason
<p>Using logstash 2.3.4-1 on centos 7 with kafka-input plugin I sometimes get </p>

<blockquote>
  <p>{:timestamp=>"2016-09-07T13:41:46.437000+0000", :message=>#0, :events_consumed=>822, :worker_count=>1, :inflight_count=>0, :worker_states=>[{:status=>"dead", :alive=>false, :index=>0, :inflight_count=>0}], :output_info=>[{:type=>"http", :config=>{"http_method"=>"post", "url"=>"${APP_URL}/", "headers"=>["AUTHORIZATION", "Basic ${CREDS}"], "ALLOW_ENV"=>true}, :is_multi_worker=>false, :events_received=>0, :workers=>"", headers=>{..}, codec=>"UTF-8">, workers=>1, request_timeout=>60, socket_timeout=>10, connect_timeout=>10, follow_redirects=>true, pool_max=>50, pool_max_per_route=>25, keepalive=>true, automatic_retries=>1, retry_non_idempotent=>false, validate_after_inactivity=>200, ssl_certificate_validation=>true, keystore_type=>"JKS", truststore_type=>"JKS", cookies=>true, verify_ssl=>true, format=>"json">]>, :busy_workers=>1}, {:type=>"stdout", :config=>{"ALLOW_ENV"=>true}, :is_multi_worker=>false, :events_received=>0, :workers=>"\n">, workers=>1>]>, :busy_workers=>0}], :thread_info=>[], :stalling_threads_info=>[]}>, :level=>:warn}</p>
</blockquote>

<p>this is the config</p>

<pre><code>        input {
      kafka {
        bootstrap_servers =&gt; "${KAFKA_ADDRESS}"
        topics =&gt; ["${LOGSTASH_KAFKA_TOPIC}"]
      }
    }

    filter {
      ruby {
        code =&gt;
      "require 'json'
       require 'base64'

       def good_event?(event_metadata)
         event_metadata['key1']['key2'].start_with?('good')
       rescue
         true 
       end

       def has_url?(event_data)
         event_data['line'] &amp;&amp; event_data['line'].any? { |i| i['url'] &amp;&amp; !i['url'].blank? }
       rescue
         false
       end

       event_payload = JSON.parse(event.to_hash['message'])['payload']

       event.cancel unless good_event?(event_payload['event_metadata'])
       event.cancel unless has_url?(event_payload['event_data'])
    "
  }
    }

    output {
      http {
          http_method =&gt; 'post'
          url =&gt; '${APP_URL}/'
          headers =&gt; ["AUTHORIZATION", "Basic ${CREDS}"]
      }

      stdout { }
    }
</code></pre>

<p>Which is odd, since it is written to logstash.log and not logstash.err</p>

<p>What does this error mean and how can I avoid it? (only restarting logstash solves it, until the next time it happens)</p>