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Red Hat Enterprise Linux (RHEL) and CentOS

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Red Hat Enterprise Linux (RHEL) and CentOS

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The following instructions show you how to prepare your hosts on Red Hat Enterprise Linux (RHEL) and on CentOS.

Check the supported Linux kernel

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Elastic Cloud Enterprise requires the default RHEL/CentOS 3.10.0-1160.31.1 or later kernel.

Use the following command to check your kernel version:
```
uname -r
```
Before you proceed, update the OS, and reboot the system.
Update the system:
```
sudo yum update
sudo reboot
```

Enable the overlay2 kernel module:

echo "overlay2" | sudo tee -a /etc/modules-load.d/overlay.conf

Refresh the dynamically generated grub2 configuration and configure grub to boot the newly installed kernel 3.10.0-1160.31.1 or later:
```
sudo grub2-set-default 0
sudo grub2-mkconfig -o /etc/grub2.cfg
```

Add the required options to the kernel boot arguments:

sudo /sbin/grubby --update-kernel=ALL --args='cgroup_enable=memory cgroup.memory=nokmem swapaccount=1'

Install Docker

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Which version of Docker you install depends on whether you use Red Hat Enterprise Linux (RHEL) or CentOS.

RHEL or CentOS 7

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If you are using RHEL/CentOS 7, install Docker version 20.10.7 or later:

Add the Docker repository:

sudo tee /etc/yum.repos.d/docker.repo <<-'EOF'
[dockerrepo]
name=Docker Repository
baseurl=https://download.docker.com/linux/centos/7/x86_64/stable
enabled=1
gpgcheck=1
gpgkey=https://download.docker.com/linux/centos/gpg
EOF

sudo yum makecache fast

On RHEL 7, enable the rhel-7-server-extras-rpm and rhel-7-server-optional-rpms repositories.

Install Docker version 20.10.7 or later:

sudo yum install -y docker-ce-20.10* docker-ce-cli-20.10* containerd.io-1.5.*

RHEL 8 or CentOS 8

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If you are using RHEL 8 or CentOS 8, install Docker version 20.10.7 or later:

Add the Docker repository:

# Add yum config manager
sudo yum install -y 'dnf-command(config-manager)'

# Add the docker-ce centos yum repo
sudo yum config-manager --add-repo=https://download.docker.com/linux/centos/docker-ce.repo

# Update the yum cache
sudo yum makecache --timer

Install Docker version 20.10.7 or later:

sudo yum install -y docker-ce-20.10* docker-ce-cli-20.10* containerd.io-1.5.*

Set up XFS quotas

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XFS quotas are required to support disk space quotas for Elasticsearch data directories. Some Linux distributions such as RHEL and CentOS already provide XFS as the default file system; however, quotas might be disabled.

Disk space quotas set a limit on the amount of disk space a cluster node can use. Currently, quotas are calculated by a static ratio of 1:32, which means that for every 1 GB of RAM a cluster is given, a cluster node is allowed to consume 32 GB of disk space.

You can use use LVM, mdadm, or a combination of the two for block device management, but this configuration is not documented nor is it supported in Elastic Cloud Enterprise.

You must use XFS on all allocators.

To set up XFS with quotas on a single, pre-partitioned block device named /dev/xvdg1:

Format the partition:
```
sudo mkfs.xfs /dev/xvdg1
```

Create the /mnt/data/ directory as a mount point:

sudo install -o $USER -g $USER -d -m 700 /mnt/data

Modify the entry for the XFS volume in the /etc/fstab file to add pquota,prjquota. The default filesystem path used by Elastic Cloud Enterprise is /mnt/data.
```
/dev/xvdg1	/mnt/data	xfs	defaults,nofail,x-systemd.automount,prjquota,pquota  0 2
```

Regenerate the mount files:

sudo systemctl daemon-reload
sudo systemctl restart local-fs.target

Update the configurations settings

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Stop the Docker service:
```
sudo systemctl stop docker
```

Configure kernel parameters:

cat <<EOF | sudo tee -a /etc/sysctl.conf
# Required by Elasticsearch 5.0 and later
vm.max_map_count=262144
# enable forwarding so the Docker networking works as expected
net.ipv4.ip_forward=1
# Decrease the maximum number of TCP retransmissions to 5 as recommended for Elasticsearch TCP retransmission timeout.
# See https://www.elastic.co/guide/en/elasticsearch/reference/current/system-config-tcpretries.html
net.ipv4.tcp_retries2=5
# Make sure the host doesn't swap too early
vm.swappiness=1
EOF

The net.ipv4.tcp_retries2 setting applies to all TCP connections and will affect the reliability of communication with systems other than Elasticsearch clusters too. If your clusters communicate with external systems over a low quality network then you may need to select a higher value for net.ipv4.tcp_retries2.

Apply the settings:

RHEL/CentOS 7:

sudo sysctl -p
sudo systemctl restart network

RHEL/CentOS 8:

sudo sysctl -p
sudo systemctl restart NetworkManager

Adjust the system limits.

Add the following configuration values to the /etc/security/limits.conf file. If you are using a user name other than elastic, adjust the configuration values accordingly.

*                soft    nofile         1024000
*                hard    nofile         1024000
*                soft    memlock        unlimited
*                hard    memlock        unlimited
elastic          soft    nofile         1024000
elastic          hard    nofile         1024000
elastic          soft    memlock        unlimited
elastic          hard    memlock        unlimited
root             soft    nofile         1024000
root             hard    nofile         1024000
root             soft    memlock        unlimited

The default limit for number of processes is too low. Remove it and rely on the kernel limit instead (for RHEL/CentOS 7 only).

sudo rm /etc/security/limits.d/20-nproc.conf

If you did not create the mount point earlier (if you did not set up XFS), create the /mnt/data/ directory as a mount point:
```
sudo install -o $USER -g $USER -d -m 700 /mnt/data
```
If you set up a new device with XFS earlier:
1. Mount the block device (change the device name if you use a different device than /dev/xvdg1):
```
sudo mount /dev/xvdg1
```
2. Set the permissions on the newly mounted device:
```
sudo chown $USER:$USER /mnt/data
```
Create the /mnt/data/docker directory for the Docker service storage:
```
sudo install -o $USER -g $USER -d -m 700 /mnt/data/docker
```
Disable the firewalld service. The service is not compatible with Docker and interferes with the installation of ECE. You must disable firewalld before installing or reinstalling ECE.
```
sudo systemctl disable firewalld
```

Configure the Docker daemon options

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Docker creates a bridge IP address that can conflict with IP addresses on your internal network. To avoid an IP address conflict, change the --bip=172.17.42.1/16 parameter in our examples to something that you know will work. If there is no conflict, you can omit the --bip parameter. The --bip parameter is internal to the host and can be set to the same IP for each host in the cluster. More information on Docker daemon options can be found in the dockerd command line reference.

Update the /etc/systemd/system/docker.service.d/docker.conf file. If the file path and file do not exist, create them.

[Unit]
Description=Docker Service
After=multi-user.target

[Service]
ExecStart=
ExecStart=/usr/bin/dockerd --data-root /mnt/data/docker --storage-driver=overlay2 --bip=172.17.42.1/16 --raw-logs --icc=false

Apply the updated Docker daemon configuration:
1. Reload the Docker daemon configuration:
```
sudo systemctl daemon-reload
```
2. Restart the Docker service:
```
sudo systemctl restart docker
```
3. Enable Docker to start on boot:
```
sudo systemctl enable docker
```
Enable your user to communicate with the Docker subsystem by adding it to the docker group:
```
sudo usermod -aG docker $USER
```
Pin the Docker version to ensure that the docker-ce package does not get upgraded:
```
echo "exclude=docker-ce" | sudo tee -a /etc/yum.conf
```

Recommended: Tune your network settings.

Create a 70-cloudenterprise.conf file in the /etc/sysctl.d/ file path that includes these network settings:

cat << SETTINGS | sudo tee /etc/sysctl.d/70-cloudenterprise.conf
net.ipv4.tcp_max_syn_backlog=65536
net.core.somaxconn=32768
net.core.netdev_max_backlog=32768
SETTINGS

Reboot your system to ensure that all configuration changes take effect:
```
sudo reboot
```
After rebooting, verify that your Docker settings persist as expected:
```
sudo docker info | grep Root
```
If the command returns Docker Root Dir: /mnt/data/docker, then your changes were applied successfully and persist as expected.

If the command returns Docker Root Dir: /var/lib/docker, then you need to troubleshoot the previous configuration steps until the Docker settings are applied successfully before continuing with the installation process. For more information, check Custom Docker daemon options in the Docker documentation.
Repeat these steps on other hosts that you want to use with Elastic Cloud Enterprise or follow the steps in the next section to start installing Elastic Cloud Enterprise.

We recommend enabling SELinux on RHEL/CentOS host systems. However, do not enable the selinux-enabled option in the Docker daemon configuration at this time.

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