Sending data from logstash to ElasticSearch (ECK): Certificate issue

[kelk (kin)]

have setup operator based elasticsearch & kibana.. but since logstash is not within ECK, running logstash as standalone. Unfortunately, i'm trying it hard to find to connect to Elasticsearch due to certificate issue.

output {
# stdout { codec => rubydebug }  
  elasticsearch {
      hosts => ["localhost:9200"]
      index => "my_index"
      document_id => "%{[@metadata][id]}"
      user => "elastic"
      password => "my_elastic_passwd"
        ssl => true
        ssl_certificate_verification => false
   }

}

with above setting, i'm getting an error: even though I've put ssl_certificate_verification=> false !!

[WARN ][logstash.outputs.elasticsearch][main] Attempted to resurrect connection to dead ES instance, but got an error. {:url=>"https://elastic:xxxxxx@localhost:9200/", 
:error_type=>LogStash::Outputs::ElasticSearch::HttpClient::Pool::HostUnreachableError, 
:error=>"Elasticsearch Unreachable: [https://elastic:xxxxxx@localhost:9200/][Manticore::ClientProtocolException] PKIX path building failed: 
sun.security.provider.certpath.SunCertPathBuilderException: 
unable to find valid certification path to requested target"}

As another method, I tried extracting the certificate as pem file and tried to load for logstash.
Like below

        ssl => true
       cacert => "/extracted/pem/file_from/eck_elastic.pem

But this also has an error, because i'm using localhost