Thanks Magnus. That's probably because of ----- symbols at the line 1.
It works good now but Logstash is not able to connect to Elasticsearch (with the same logstash.conf file as posted above):
Sending Logstash's logs to /usr/share/logstash/logs which is now configured via log4j2.properties
[2017-04-12T05:15:10,695][INFO ][logstash.outputs.elasticsearch] Elasticsearch pool URLs updated {:changes=>{:removed=>[], :added=>[http://logstash_system:xxxxxx@elasticsearch:9200/_xpack/monitoring/?system_id=logstash&system_api_version=2&interval=1s]}}
[2017-04-12T05:15:10,759][INFO ][logstash.outputs.elasticsearch] Running health check to see if an Elasticsearch connection is working {:healthcheck_url=>http://logstash_system:xxxxxx@elasticsearch:9200/, :path=>"/"}
[2017-04-12T05:15:11,751][WARN ][logstash.outputs.elasticsearch] Attempted to resurrect connection to dead ES instance, but got an error. {:url=>#<URI::HTTP:0x78dc6c70 URL:http://logstash_system:xxxxxx@elasticsearch:9200/_xpack/monitoring/?system_id=logstash&system_api_version=2&interval=1s>, :error_type=>LogStash::Outputs::ElasticSearch::HttpClient::Pool::HostUnreachableError, :error=>"Elasticsearch Unreachable: [http://logstash_system:xxxxxx@elasticsearch:9200/][Manticore::SocketException] Connection refused (Connection refused)"}
[2017-04-12T05:15:11,771][INFO ][logstash.outputs.elasticsearch] New Elasticsearch output {:class=>"LogStash::Outputs::ElasticSearch", :hosts=>[#<URI::HTTP:0x253a12a5 URL:http://elasticsearch:9200>]}
[2017-04-12T05:15:11,772][INFO ][logstash.pipeline ] Starting pipeline {"id"=>".monitoring-logstash", "pipeline.workers"=>1, "pipeline.batch.size"=>2, "pipeline.batch.delay"=>5, "pipeline.max_inflight"=>2}
[2017-04-12T05:15:11,801][INFO ][logstash.pipeline ] Pipeline .monitoring-logstash started
[2017-04-12T05:15:11,909][INFO ][logstash.outputs.elasticsearch] Elasticsearch pool URLs updated {:changes=>{:removed=>[], :added=>[http://elasticsearch:9200/]}}
[2017-04-12T05:15:11,913][INFO ][logstash.outputs.elasticsearch] Running health check to see if an Elasticsearch connection is working {:healthcheck_url=>http://elasticsearch:9200/, :path=>"/"}
[2017-04-12T05:15:11,932][WARN ][logstash.outputs.elasticsearch] Attempted to resurrect connection to dead ES instance, but got an error. {:url=>#<URI::HTTP:0x5a382205 URL:http://elasticsearch:9200/>, :error_type=>LogStash::Outputs::ElasticSearch::HttpClient::Pool::HostUnreachableError, :error=>"Elasticsearch Unreachable: [http://elasticsearch:9200/][Manticore::SocketException] Connection refused (Connection refused)"}
[2017-04-12T05:15:11,947][INFO ][logstash.outputs.elasticsearch] Using mapping template from {:path=>nil}
[2017-04-12T05:15:12,018][WARN ][logstash.outputs.elasticsearch] Marking url as dead. Last error: [LogStash::Outputs::ElasticSearch::HttpClient::Pool::HostUnreachableError] Elasticsearch Unreachable: [http://elasticsearch:9200/][Manticore::SocketException] Connection refused (Connection refused) {:url=>http://elasticsearch:9200/, :error_message=>"Elasticsearch Unreachable: [http://elasticsearch:9200/][Manticore::SocketException] Connection refused (Connection refused)", :error_class=>"LogStash::Outputs::ElasticSearch::HttpClient::Pool::HostUnreachableError"}
[2017-04-12T05:15:12,024][ERROR][logstash.outputs.elasticsearch] Failed to install template. {:message=>"Elasticsearch Unreachable: [http://elasticsearch:9200/][Manticore::SocketException] Connection refused (Connection refused)", :class=>"LogStash::Outputs::ElasticSearch::HttpClient::Pool::HostUnreachableError", :backtrace=>["/usr/share/logstash/vendor/bundle/jruby/1.9/gems/logstash-output-elasticsea
...
[2017-04-12T05:15:53,163][WARN ][logstash.outputs.elasticsearch] Attempted to resurrect connection to dead ES instance, but got an error. {:url=>#<URI::HTTP:0x5a382205 URL:http://elasticsearch:9200/>, :error_type=>LogStash::Outputs::ElasticSearch::HttpClient::Pool::BadResponseCodeError, :error=>"Got response code '401' contacting Elasticsearch at URL 'http://elasticsearch:9200/'"}
[2017-04-12T05:15:53,279][WARN ][logstash.outputs.elasticsearch] Restored connection to ES instance {:url=>#<URI::HTTP:0x4d57ba1a URL:http://logstash_system:xxxxxx@elasticsearch:9200/>}
[2017-04-12T05:15:58,167][INFO ][logstash.outputs.elasticsearch] Running health check to see if an Elasticsearch connection is working {:healthcheck_url=>http://elasticsearch:9200/, :path=>"/"}
[2017-04-12T05:15:58,178][WARN ][logstash.outputs.elasticsearch] Attempted to resurrect connection to dead ES instance, but got an error. {:url=>#<URI::HTTP:0x5a382205 URL:http://elasticsearch:9200/>, :error_type=>LogStash::Outputs::ElasticSearch::HttpClient::Pool::BadResponseCodeError, :error=>"Got response code '401' contacting Elasticsearch at URL 'http://elasticsearch:9200/'"}
[2017-04-12T05:16:03,184][INFO ][logstash.outputs.elasticsearch] Running health check to see if an Elasticsearch connection is working {:healthcheck_url=>http://elasticsearch:9200/, :path=>"/"}
[2017-04-12T05:16:06,158][WARN ][logstash.outputs.elasticsearch] Attempted to resurrect connection to dead ES instance, but got an error. {:url=>#<URI::HTTP:0x5a382205 URL:http://elasticsearch:9200/>, :error_type=>LogStash::Outputs::ElasticSearch::HttpClient::Pool::BadResponseCodeError, :error=>"Got response code '401' contacting Elasticsearch at URL 'http://elasticsearch:9200/'"}
[2017-04-12T05:16:09,159][INFO ][logstash.outputs.elasticsearch] Running health check to see if an Elasticsearch connection is working {:healthcheck_url=>http://elasticsearch:9200/, :path=>"/"}
[2017-04-12T05:16:09,166][WARN ][logstash.outputs.elasticsearch] Attempted to resurrect connection to dead ES instance, but got an error. {:url=>#<URI::HTTP:0x5a382205 URL:http://elasticsearch:9200/>, :error_type=>LogStash::Outputs::ElasticSearch::HttpClient::Pool::BadResponseCodeError, :error=>"Got response code '401' contacting Elasticsearch at URL 'http://elasticsearch:9200/'"}
[2017-04-12T05:16:14,168][INFO ][logstash.outputs.elasticsearch] Running health check to see if an Elasticsearch connection is working {:healthcheck_url=>http://elasticsearch:9200/, :path=>"/"}
Do you have any ideas what could be wrong?