containers/elk/logstash-forwarder/conf/config.json

{
  "network": {
    "servers": [ "logstash:5043" ],
    "ssl certificate": "/opt/certs/logstash-forwarder.crt",
    "ssl key": "/opt/certs/logstash-forwarder.key",
    "ssl ca": "/opt/certs/logstash-forwarder.crt",
    "timeout": 15
  },
  "files": [
    {
      "paths": [ "/var/log/message", "/var/log/syslog" ],
      "fields": { "type": "stdin" }
    }
  ]
}