Elasticsearch official documentation
https://www.elastic.co/guide/en/elasticsearch/reference/6.x/index.html
Very good Elasticsearch Guide on Github
https://github.com/dzharii/awesome-elasticsearch
Elasticsearch Official forum
https://discuss.elastic.co/
Stackoverflow elasticsearch handlers
http://stackoverflow.com/questions/tagged/elasticsearch
Jolicode elasticsearch Cheatsheet
http://elasticsearch-cheatsheet.jolicode.com/
Elasticsearch DevOpsSchool reference
https://www.devopsschool.com/blog/category/elastic-stack/
https://www.devopsschool.com/tutorial/elastic/