Wido den Hollander – Page 19

Installing and testing NixOS

NixOS

NixOS is a minimal and flexible Linux distribution which doesn’t use any of the existing package manager.

NixOS is a Linux distribution with a unique approach to package and configuration management. Built on top of the Nix package manager, it is completely declarative, makes upgrading systems reliable, and has many other advantages.

I wanted to test NixOS and see if it could be a candidate for a very minimal KVM hypervisor running just Qemu, libvirt and Apache CloudStack.

With this post I just wanted to share how you can quickly install NixOS inside a VirtualBox VM.

VirtualBox

On my desktop and laptop I usually use VirtualBox to quickly test something inside Virtual Machines. In this case I downloaded the NixOS minimal 64-bit ISO and created a VM:

1024MB of memory
8GB SATA disk
NixOS ISO attached

Installation

After you start the VM it will boot from the ISO. You will then find yourself in a root prompt saying just nixos.

The first step is to format your disk and mount it under /mnt.

parted /dev/sda mklabel msdos
parted /dev/sda mkpart primary 0% 100%
mkfs.xfs /dev/sda1
mount /dev/sda1 /mnt

If you have that done you can run:

nixos-generate-config

This will generate /mnt/etc/nixos/configuration.nix from where you can configure your OS.

This is what I used as my configuration:

{ config, pkgs, ... }:

{
  imports = [
      ./hardware-configuration.nix
    ];

  boot.loader.grub.enable = true;
  boot.loader.grub.version = 2;
  boot.loader.grub.device = "/dev/sda";

  boot.kernelPackages = pkgs.linuxPackages_4_1;

  time.timeZone = "Europe/Amsterdam";

  networking.firewall.enable = false;

  environment.systemPackages = with pkgs; [
    wget git screen ceph
  ];

  services.openssh.enable = true;
  services.openssh.permitRootLogin = "yes";

  virtualisation.libvirtd.enable = true;
  virtualisation.libvirtd.extraOptions = ["-l"];
  virtualisation.libvirtd.extraConfig = "listen_tls = 0\nlisten_tcp = 1";

  system.stateVersion = "15.09";
}

A minimal installation with just OpenSSH and libvirt installed.

Now you can actually install NixOS:

nixos-install

After a few minutes you will be prompted for a root-password and that’s it!

Reboot and you have a running NixOS installation 🙂

Using TRIM/DISCARD with Ceph RBD and libvirt

TRIM/DISCARD

Using TRIM/DISCARD you can give back free space to a Ceph cluster. Normally, any thin provisioned block device will keep on growing until its maximum size while being used. Using the DISCARD command a underlying block device can be instructed to discard blocks which do not contain data.

In the case of Ceph’s RBD we can shrink our RBD images again which gives us back free space in our Ceph cluster.

Libvirt

Using this feature is only supported if you use VirtIO-SCSI and not if you use plain VirtIO.

Some searching brought me to this XML for my Ubuntu 15.10 guest:

<disk type='network' device='disk'>
  <driver name='qemu' type='raw' cache='none' discard='unmap'/>
  <auth username='admin'>
    <secret type='ceph' uuid='f94812dd-f06f-48f6-9839-1edf7ee8f8d6'/>
  </auth>
  <source protocol='rbd' name='libvirt/image1'>
    <host name='hostname.of.my.ceph.monitor'/>
  </source>
  <target dev='sda' bus='scsi'/>
  <controller type='scsi' index='0' model='virtio-scsi'/>
</disk>

Inside the guest

I tried a Ubuntu 15.10 guest but this should be supported in any other modern Linux guest.

lspci shows me:

root@ubuntu1510:~# lspci 
00:00.0 Host bridge: Intel Corporation 440FX - 82441FX PMC [Natoma] (rev 02)
00:01.0 ISA bridge: Intel Corporation 82371SB PIIX3 ISA [Natoma/Triton II]
00:01.1 IDE interface: Intel Corporation 82371SB PIIX3 IDE [Natoma/Triton II]
00:01.2 USB controller: Intel Corporation 82371SB PIIX3 USB [Natoma/Triton II] (rev 01)
00:01.3 Bridge: Intel Corporation 82371AB/EB/MB PIIX4 ACPI (rev 03)
00:02.0 VGA compatible controller: Cirrus Logic GD 5446
00:03.0 Ethernet controller: Red Hat, Inc Virtio network device
00:04.0 SCSI storage controller: LSI Logic / Symbios Logic 53c895a
root@ubuntu1510:~#

And I have a sda block device which my guest uses:

root@ubuntu1510:~# df -h
Filesystem      Size  Used Avail Use% Mounted on
udev            230M     0  230M   0% /dev
tmpfs            49M  4.6M   45M  10% /run
/dev/sda1       9.3G  1.3G  7.6G  15% /
tmpfs           245M     0  245M   0% /dev/shm
tmpfs           5.0M     0  5.0M   0% /run/lock
tmpfs           245M     0  245M   0% /sys/fs/cgroup
tmpfs            49M     0   49M   0% /run/user/0
root@ubuntu1510:~#

Now I can run fstrim which will trim the block device:

root@ubuntu1510:~# fstrim -v /
/: 128 MiB (134217728 bytes) trimmed
root@ubuntu1510:~#

The Ceph Trafficlight

At PCextreme we have a 700TB Ceph cluster which is used behind our public cloud Aurora Compute which runs Apache CloudStack.

Ceph health

One of the things we monitor of the Ceph cluster is it’s health. This can be OK, WARN or ERR. It speaks for itself that you always want to see OK, but things do go wrong. Disks fail, machines die, kernel panics happen. Stuff goes wrong.

I thought it was a cool idea to buy a used real traffic light which I could install at the office. OK would be green, WARN would be orange/amber and ERR would be red.

2nd hand Trafficlight

Some searching on the internet brought me to trafficlightshop.com. They sell used (Dutch) traffic lights. I bought a Vialis 2230 (The largest on the picture below).

For EUR 75,00 I got my hands on a original trafficlight!

Controlling the lights

When I got the trafficlight it was already equipped with LED lights which work on 230V. A 30cm cable (cut off) was sticking out with 4 wires in it:

Blue: Neutral
Green: Phase/Positive for Green
Yellow: Phase/Positive for Orange/Amber
Red: Phase/Positive for Red

It was easy. All I had to do was buy a add-on board for a Raspberry Pi so I could control the lights.

Solid State Relay

My search for a add-on board brought me to BitWizard.nl, they make all kinds of add-on boards for the Raspberry Pi.

One of them is a SSR (Solid State Relay) board which has 4 outputs. Their wiki explained that it was very simple to control the Relays using Python.

A quick test at my desk at home brought be to a working setup.

Addition components

After writing the code which controls the light it was time to buy some housing where I could install it in.

At Conrad I found the things I needed. A housing, some connectors and some cabling. A overview of my order:

This was needed since I would install it at the office and it needed to be safe. You don’t want somebody to get shocked by 230V. That’s kind of dangerous.

Bringing it together

It was time to start drilling and soldering! In my shed it looked like this:

And a few more pictures of building it. Took me about 3 hours to complete.

At the office

The next day it was time to install it at the office! Some drilling and the result:

Health OK: Green

Health WARN: Amber/Orange

Health ERR: Red

No picture! We can trigger a WARN state in Ceph without service interruptions, but not a ERR state.

The code

The Python code I wrote is all on Github. It’s just some Python code which polls our Ceph dashboard every second. If the status changes it also changes the traffic light.