Connection marked as failed because the onConnect callback failed

Thank you for reply, but in my case problem was '/' in the end of hosts: ["http://10.0.10.209:9200/"]; so current configuration is following:

filebeat.prospectors:
- input_type: log
  paths:
    - 'C:\Projects\Utils\FileBeats\sample\log.json'

output.elasticsearch:
  hosts: ["http://10.0.10.209:9200"]
  template.name: filebeat
  template.path: filebeat.template.json