How to fix Graylog-Server Couldn't read cluster

The issue is the Graylog cannot connect to Elasticsearch
Read more about Elasticsearch
https://www.elastic.co/guide/en/elast...

The following commands will fix the issue:
1- First remove the elasticsearch
$ apt remove --purge elasticsearch
2- Use the following commands
$ wget -qO - https://packages.elastic.co/GPG-KEY-e... | apt-key add -
$ echo "deb https://packages.elastic.co/elasticse... stable main" | tee -a /etc/apt/sources.list.d/elasticsearch-2.x.list
$ apt update
$ apt install elasticsearch