path: root/2021-06-21-virtual-machines.md

# Virtual machines: what?

* A program that emulates a physical computer: CPU, RAM, hard drives,
  networking, screen, keyboard, mouse, etc
  
* More or less faithful to real hardware

-----------------------------------------------------------------------------

# Virtual machines: why?

* Can hit with a bat, axe, hammer.

* Can be version controlled.

* Easy to create with desired virtual hardware configuration

* Share physical hardware resources more efficiently

-----------------------------------------------------------------------------

# Why not containers?

* Possibly less secure than virtual machines (jury is still out)

* Containers and host share kernel instance, CPU; can't use
  different CPU architecture, operating system than host

* But containers start faster, are easier to use, when they suit the
  use case.

-----------------------------------------------------------------------------

# Virtualisation options

* VirtualBox, QEmu, KVM, Xen, libvirt, ...

* I use KVM + QEmu orchestrated by libvirt

-----------------------------------------------------------------------------

# What you need: Linux + KVM

* Enable virtualization in BIOS, rest should be automatic.

* `lsmod | grep kvm`

* `ls -l /dev/kvm`

* [`https://wiki.debian.org/KVM`](https://wiki.debian.org/KVM)

-----------------------------------------------------------------------------

# libvirt + friends

- `apt install virt-manager virt-install libvirt-clients libnss-libvirt`

- `sudo adduser $USER libvirt`

- log out, back in

- `virsh -c qemu:///system net-start default`

- `virsh -c qemu:///system net-autostart default`

- edit `/etc/nsswitch.conf`, line with `hosts`,  
  include `libvirt libvirt_guest`

-----------------------------------------------------------------------------

# Install Debian in a VM: virt-manager

* Download ISO image: `get.debian.org`

  - `debian-10.9.0-amd64-netinst.iso`, and `SHA256SUMS`

  - check validity:  
    `sha256sum -c SHA256SUMS --ignore-missing`

* start `virt-manager`

  - unless you already did the `virsh` magic earlier: 
    activate default network via  
    Edit → Connection details → Virtual networks →
    default

  * create new VM with virt-manager

* log in via ssh

-----------------------------------------------------------------------------

# Create VM with virt-install

```sh
virt-install \
  --name "${name}" --connect qemu:///system \
  --virt-type kvm --memory 2048 --vcpus 2 \
  --boot hd,menu=off -disk path="${image},device=disk" \
  --graphics vnc --os-type Linux --os-variant debian10 \
  --console pty,target_type=serial --noautoconsole \
  --import
```

* use OpenStack image from `cloud.debian.org`
  - needs a `cloud-init` ISO image with config to set up SSH access,
    hostname
  - not _difficult_ to make, but a bit of a bother
* or custom image made some way

-----------------------------------------------------------------------------

# Manual SSH known host key management is so 90s

* Every new VM has a new host key

  - create VM, SSH is tiresome
  - delete VM, create new VM with same name, SSH is really upset:
    YOU ARE UNDER ATTACK! HELP! HELP! PANIC!

* SSH CA and host certificates is bliss

  - create CA key
  - sign host key with CA key → host certificate
  - configure SSH client to accept certificates made with CA key
  - new hosts, re-created hosts are silently accepted
  - security **and** comfort is bliss!

-----------------------------------------------------------------------------

# SSH CA


* create CA key:  
  `ssh-keygen -f ~/.ssh/ca -N '' -t ed25519`

- edit `~/.ssh/known_hosts` to have a line with  
 `@cert-authority * ssh-ed25519 AAAA....`

- make and install the host certificate:  
  `ssh-keygen -s ~/.ssh/ca -I "my SSH CA v1" \  
  -h -n shell.example.com host.key.pub`

  - install `host.key-cert.pub` on server `/etc/ssh`
  
  - edit `/etc/ssh/sshd_config` to point to certificate

  - still a bit tedious, but can be automated

  - [`https://liw.fi/sshca/`](https://liw.fi/sshca/)

-----------------------------------------------------------------------------

# Install and configure vmadm

Create `~/.config/vmadm/config.yaml`

```yaml
image_directory: ~/vm-talk
default_base_image: ~/vm-talk/debian-10-openstack-amd64.qcow2
default_image_gib: 5
default_memory_mib: 2048
default_cpus: 1
default_generate_host_certificate: true
default_autostart: true
ca_key: ~/.ssh/ca
authorized_keys:
  - ~/.ssh/liw-openpgp.pub
```

-----------------------------------------------------------------------------

# Create a vmadm specification

* Create `toys.yaml`, using defaults from configuration (or override
  attributes per-VM, as needed):

```yaml
toy1: {}
toy2: {}
```

* Manage VMs as a group.

  * `vmadm new toys.yaml`
  * `ssh debian@toy1`
  * `ssh debian@toy2`
  * `vmadm delete toys.yaml`

-----------------------------------------------------------------------------

# Create VM image using vmdb2

* A VM image is a file is used as a virtual hard disk. Installing
  operating system can be done manually, or automated from a
  specification file.
  
-----------------------------------------------------------------------------

```{.yaml .numberLines}
steps:
  - mkimg: "{{ output }}"
    size: 4G

  - mklabel: msdos
    device: "{{ output }}"

  - mkpart: primary
    device: "{{ output }}"
    start: 0%
    end: 100%
    tag: rootfs

  - kpartx: "{{ output }}"

  - mkfs: ext4
    partition: rootfs

  - mount: rootfs
```

-----------------------------------------------------------------------------

```{.yaml .numberLines}
  - unpack-rootfs: rootfs

  - debootstrap: buster
    target: rootfs
    mirror: http://deb.debian.org/debian
    unless: rootfs_unpacked

  - apt: install
    tag: rootfs
    packages:
      - linux-image-amd64
    unless: rootfs_upacked

  - cache-rootfs: rootfs
    unless: rootfs_upacked

  - fstab: rootfs
  - grub: bios
    tag: rootfs
```

------------------------------------------------------------------------------

```sh
sudo vmdb2 toy.vmdb --output toy.raw  \
  --verbose --rootfs-tarball toy.tar.gz \
  --log toy.log
```
  
* simplistic example: doesn't sets hostname or SSH access

  - could be done, via Ansible
  - or install `cloud-init` in image

* convert image:  
  `qemu-img convert -O qcow2 toy.raw toy.qcow2`

* tool could be polished a lot, but works

---
title: "Computers you can't hit with a bat"
subtitle: A brief introduction to virtual machines
author: Lars Wirzenius
date: 2021-06-21
...