Preparing the Search Cluster

To prepare the search servers for Elasticsearch, perform the following steps.

Verify your servers against the Hardware Requirements for Elasticsearch.
Appropriately cable the servers to your network infrastructure so that, once configured, they will be reachable from the Swarm nodes.
Install RHEL/CentOS 7 Linux and apply any required updates. For questions about enabling or disabling IPv6, contact Support.
Best practice

Use RHEL/CentOS Minimal Server (with Compatibility Libraries), which is the standard for Swarm development and testing. RHEL/CentOS Desktop consumes extra resources that Elasticsearch can use, alters the OS configuration to emphasize user interface vs. server performance, and requires additional updating and security maintenance.
Configure the servers with static IP addresses.
Configure DNS, if desired.
Adjust the server firewall rules. See https://firewalld.org.
If on CentOS 7 you install and run iptables, you must adjust the rules to permit the following ports:
- Allow public access on these ports:
```
firewall-cmd --permanent --zone=public --add-port=9200/tcp
firewall-cmd --permanent --zone=public --add-port=9300/tcp
firewall-cmd --reload
```
- For SwarmFS access, search the Support portal for SwarmNFS 2.x - Access to Elasticsearch (IPTables).
  Important
  Elasticsearch 7 bundles its own Java so there is no need to install OpenJDK for it. If you have already installed it earlier for Elasticsearch 6, then use the below command to remove the installed OpenJDK.
  Remove OpenJDK Package
  
  yum remove java-1.8.0-openjdk