How to Create a RHEL 8 Image for Hetzner Root Servers

hetznerplus_signrhel-linux-8

Overview

In this article I will explain how to create your own custom RHEL 8 image for hetzner root servers. Hetzner offers new and used physical servers on a per/month basis (https://www.hetzner.de/sb). They offer extremely competitive pricing. These servers are perfect for demo or lab environments where you are operating your own platform and want it running 24/7!

Hetzner unfortunately does not offer RHEL images however, does provide a means for bringing your own image. A colleague of mine, Ingo Boernig, already shared a blog on how to do this for RHEL 7.5. This article with cover RHEL 8.0.

Install RHEL 8 in a VM

Download RHEL 8 ISO DVD from https://access.redhat.com/downloads/content/479/ver=/rhel—8/8.0/x86_64/product-software. Using KVM virt-manager (or another hypervisor) install RHEL 8 in a VM.

rhel8-1

Once the VM boots follow the installation and use defaults. Select minimal server from the software selection. Also configure network to boot using DHCP.

rhel8-2

Prepare RHEL 8 VM for Hetzner

Log into the VM using ssh or console.

Hetzner only supports one boot kernel. As such we will remove the rescue kernel.

# rm /boot/vmlinuz-0-rescue-adcc72dfe3ed4c049ffff0ec950a90d9
# rm /boot/initramfs-0-rescue-adcc72dfe3ed4c049ffff0ec950a90d9.img

Hetzner creates a ram disk and uses the dracut tool. It expects dracut to be installed under /sbin. This is not the case with RHEL 8 so we will add a symlink.

# ln -s /usr/bin/dracut /sbin/dracut

Finally create a tar zip of the RHEL 8 OS. The image needs to be called CentOS-75-el-x86_64-minimal.tar.xz because Hetzner is expecting certain image names but I assure you this will be RHEL 8.

# tar cJvf CentOS-75-el-x86_64-minimal.tar.xz --exclude=/dev \
--exclude=/proc --exclude=/sys --exclude=/CentOS-75-el-x86_64-minimal.tar.xz /

Deploy Image on Hetzner Server

In order to install OS or repair it you need to get into Hetner server rescue mode.

hetzner_1

hetzner_2

hetzner_3

Using secure copy, upload the image to the Hetzner server /root directory.

# scp CentOS-75-el-x86_64-minimal.tar.xz root@hetzner_ip:/root

Log into your Hetzner server using your ssh key. You should be placed into rescue mode.

Create a Hetzner configuration and use your custom image

root@rescue# vi config.txt

DRIVE1 /dev/sda 
DRIVE2 /dev/sdb 
SWRAID 1 
SWRAIDLEVEL 0 
BOOTLOADER grub 
HOSTNAME keithcloud.lab 
PART /boot ext3 512M 
PART lvm vg0 150G 

LV vg0 root / ext4 50G 
LV vg0 swap swap swap 8G 
LV vg0 var /var ext4 10G 
LV vg0 tmp /tmp ext4 30G

IMAGE /root/CentOS-75-el-x86_64-minimal.tar.xz

Install Image on root server.

Note: You will likely see an error because Hetzner will want perform a dnf update as last step. On a RHEL image this won’t work as you haven’t setup a subscription. This error is safe to ignore.

root@rescue# installimage -a -c config.txt

Hetzner Online GmbH - installimage

Your server will be installed now, this will take some minutes
You can abort at any time with CTRL+C ...

: Reading configuration done 
: Loading image file variables done 
: Loading centos specific functions done 
1/18 : Deleting partitions done 
2/18 : Test partition size done 
3/18 : Creating partitions and /etc/fstab done 
4/18 : Creating software RAID level 0 done 
5/18 : Creating LVM volumes done 
6/18 : Formatting partitions
: formatting /dev/md/0 with ext3 done 
: formatting /dev/vg0/root with ext4 done 
: formatting /dev/vg0/swap with swap done 
: formatting /dev/vg0/var with ext4 done 
: formatting /dev/vg0/tmp with ext4 done 
: formatting /dev/vg0/home with ext4 done 
7/18 : Mounting partitions done 
8/18 : Sync time via ntp done 
9/18 : Downloading image (http) done 
: Importing public key for image validation done 
10/18 : Validating image before starting extraction warn 
: No detached signature file found!
11/18 : Extracting image (http) done 
12/18 : Setting up network config done 
13/18 : Executing additional commands
: Setting hostname done 
: Generating new SSH keys done 
: Generating mdadm config done 
: Generating ramdisk done 
: Generating ntp config done 
14/18 : Setting up miscellaneous files done 
15/18 : Configuring authentication
: Fetching SSH keys done 
: Disabling root password done 
: Disabling SSH root login without password done 
: Copying SSH keys done 
16/18 : Installing bootloader grub done 
17/18 : Running some centos specific functions failed

An error occured while installing the new system!
See the debug file /root/debug.txt for details.

Reboot root server.

root@rescue# reboot now

Log back into Hetzner root server and verify RHEL version.

[root@keithcloud ~]# cat /etc/redhat-release
Red Hat Enterprise Linux release 8.0 (Ootpa)

Summary

In this article we showed how to build a custom RHEL 8 image for Hetzner servers. Feedback is always welcome so please don’t be shy.

Happy Clouding!

(c) 2019 Keith Tenzer

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