How to configure a CoreOS system

What is CoreOS ?

CoreOS is a minimal Linux system that uses Linux containers to manage services at a higher level of abstraction. A single service's code and all dependencies are packaged within a container that can be run on one or many CoreOS machines.

CoreOS are essentially based on docker containers.

I invite you to read the CoreOS documentation on : https://coreos.com/docs/

I also invite you to watch a real case of deploying CoreOS : https://youtu.be/vEpV56iglyc

How to install CoreOS ?

First download the last ISO file on CoreOS website.

When you booted on the system run this command to configure the proxy to be able to download all update and final install

sudo -i export http_proxy="http://proxy.YOURDOMAIN.lan:9876"

sudo -i export https_proxy="https://proxy.YOURDOMAIN.lan:9876"

By using this simple command you will install it on your disk however you need to configure a password first or you will be not able to login to the system

sudo -i coreos-install -d /dev/sda -C stable

Here the option of COREOS-INSTALL

-d DEVICE   Install CoreOS to the given device.

-V VERSION  Version to install (e.g. current)

-C CHANNEL  Release channel to use (e.g. beta)

-o OEM      OEM type to install (e.g. openstack)

-c CLOUD    Insert a cloud-init config to be executed on boot.

-t TMPDIR   Temporary location with enough space to download images.

-v          Super verbose, for debugging.

-b BASEURL  URL to the image mirror

CoreOS Installation with Config Script

CoreOS enable you to have a script configuration to allow you to quickly deploy it.

Here the documentation I use to write the config file : https://coreos.com/os/docs/latest/cloud-config.html#configuration-file

When running the fist installation I use this simple script :

#cloud-config

hostname: NAME OF YOUR SERVER

users:

- name: root

  passwd: $6$rounds=4096$MpWe4fTP6BKFuM$hp3jCdndGnuhMMi59cyXlHY7tewmCF8LLuClLhw0V8lvlLFRHXfWD4ujm3hM5gm5x9El06ubEAg1HulESKk081

This config file will just allow you to configure the root password to Soleil just after the installation.

to install CoreOS with the script run the this command

sudo -i coreos-install -d /dev/sda -C stable -c cloud-config-file

How to add a second disk with LVM

By default, All the installation are make on a single disk with no LVM on it, so I decide to put the /var on a second disk with LVM

Make sure to add the second disk to your CoreOS VM.

I make a configuration script after CoreOS have been booted to configure the disk and download the new configuration file to always mount the disk :

#!/bin/sh

if [ "$(id -u)" != "0" ]; then

echo "This script must be run as root" 1>&2

exit 1

fi

echo " Change the SSH KEY"

rm /etc/ssh/ssh_host_*

systemctl restart sshd-keygen.service

echo " Create  the disk on LVM "

pvcreate /dev/sdb

echo " Create  the LVM, VG and LV "

vgcreate vg_var /dev/sdb

lvcreate -L 40G -n lv_var vg_var

mkfs.ext4 /dev/vg_var/lv_var

echo " Create mount point for the new disk on /media/data "

mkdir /media/data

echo " Mount the new LV to /media/data "

mount /dev/vg_var/lv_var /media/data

echo " modify the /var/lib/coreos-install/user_data to mount the new disk on every reboot "

wget http://10.101.0.106/coreos/cloud-config

cp /dev/null /var/lib/coreos-install/user_data

cat cloud-config >> /var/lib/coreos-install/user_data

Here the downloaded configuration file that mount the disk and enable docker :

#cloud-config

hostname: cor-pdt-toolbox

users:

  - name: root

    passwd: $6$rounds=4096$MpWe4fTP6BKFuM$hp3jCdndGnuhMMi59cyXlHY7tewmCF8LLuClLhw0V8lvlLFRHXfWD4ujm3hM5gm5x9El06ubEAg1HulESKk081

coreos:

  units:

    - name: media-data.mount

      command: start

      content: |

        [Mount]

        What=/dev/vg_var/lv_var

        Where=/media/data

        Type=ext4

write_files:

    - path: /etc/systemd/system/docker.service.d/http-proxy.conf

      owner: core:core

      permissions: 0644

      content: |

        [Service]

        Environment="HTTP_PROXY=http://proxy.YOURDOMAIN.lan:9876"

        Environment="HTTPS_PROXY=http://proxy.YOURDOMAIN.lan:9876"

    - path: /etc/systemd/system/basic.target.wants/systemd-reboot.timer

      content: |

        [Unit]

        Description=Daily reboot

        [Timer]

        OnCalendar=daily

        [Install]

        WantedBy=basic.target

coreos:

  units:

    - name: docker.service

      command: restartpvs

write_files:

    - path: /etc/ssh/sshd_config

      permissions: 0600

      owner: root:root

      content: |

        # Use most defaults for sshd configuration.

        UsePrivilegeSeparation sandbox

        Subsystem sftp internal-sftp

        ClientAliveInterval 180

        UseDNS no

        PermitRootLogin yes

        PasswordAuthentication yes

write_files:

    - path: /etc/systemd/journald.conf

      content: |

        [Journal]

        SystemMaxUse=50M

The CoreOS node are now ready to use

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