Lxd
LXD and LXC#
LXC - Linux Containers, a userspace interface using the host’s kernel LXD - An extension to LXC adding a Rest API - an alternative to LXC’s tools
The lightervisor
A System container manager, offering a similar user experience to virtual machines but using linux containers instead.
- Image based with pre-made images for a wide number of linux distributions
- Built around a REST API
- Designed to run full machine containers - as opposed to docker and rocket that run process based containers
- High density - number of containers you can run
- Feels the same as a full machine
- Security focus - all processes not run as root
The LXD daemon only works on Linux but the client tool (lxc) is available on most platforms
Commands#
View loaded images
lxc image list
You can also view available images on their website
There are 3 default image servers:
- ubuntu
- ubuntu-daily
- images
List stable ubuntu images
lxc image list ubuntu: | less
Launch an image
lxc launch ubuntu:18.04 first
View current server configuration
lxc config show
The new image will be visible in the list now
lxc list
Get running details
lxc info first
lxc config show first
Limiting Resources#
By default your container comes with no resource limitation and inherits from the parent environment
free -m
lxc exec first -- free -m
To apply a memory limit to a container
lxc config set first limits.memory 128MB
Confirm it has been applied
lxc exec first -- free -m
Snapshots#
LXD supports snapshotting and restoring container snapshots
Make a snapshot called clean:
lxc snapshot first clean
Restore everything to the snapshotted state:
lxc restore first clean
Confirm everything is back to normal
lxc exec first -- bash
Creating Images#
To publish an existing container
lxc publish first/clean --alias clean-ubuntu
Delete the initial contains
lxc stop first
lxc delete first
Launch a container from the existing image
lxc launch clean-ubuntu second
Stop and delete
lxc delete --force second
Accessing files from the container#
Pull a file from the container
lxc file pull second/etc/hosts .
Push a file to the container
lxc file push hosts second/etc/hosts
Access log files
lxc file pull second/var/log/syslog - | less
Use a remote image server#
List available images
lxc image list images: | less
Spawn a centos container
lxc launch images:centos/7 third
Confirm it is centos
lxc exec third -- cat /etc/redhat-release
Delete it
lxc delete -f third
List all configured remotes
lxc remote list
List remote container images
lxc list tryit:
List images
lxc image list tryit:
Launch a local image on a remote LXD
lxc launch clean-ubuntu tryit:fourth
Spawn a shell inside the remote
lxc exec tryit:fourth bash
Copy that container
lxc copy tryit:fourth tryit:fifth
Move it back to our local lxd
lxc move tryit:fifth sixth
NC-LXD#
Drop in replacement for libVirt KVM driver - to manage LXD containers in an Openstack cloud.
LXD vs KVM#
In KVM the virtual machine has all the same things as bare metal - bios, bootloader, linux kernel, host OS then can you only run your workload. In LXD there is none of that, containers run as processes directly on the host - no bios, no device drivers.
Density#
Intel server 4 core, 16 Gb and setup ubuntu on it. Launch KVM instances with an ubuntu image until we run out of hypervisor resources and do the same thing with LXD.
The VM’s were 512mb.
KVM launched 36. LXD launched over 600, of the same image. A much lower memory footprint.
LXD is frugal with memory
Startup Time#
How fast the instances are created
LXD - 1.5 seconds KVM - 25 seconds
- 37 KVM instances launched in 943 seconds
- 536 LXD guests in 828 seconds
Network Latency#
KVM packet through networking layer into host, to bridge and wake up other host etc. With LXD with the same test, there is not as much to go through so apps communicate 50% faster
Even local latency with 2 threads needing to be scheduled and context switched between, LXD was 50% faster.
OS Limitations#
You can run a windows or mac VM on a KVM instance. Only something that runs on a linux container will work on LXD. You could run centOS but you will get the ubuntu kernel.
Limitations#
On LXD cannot mount within a guest instances, you have to ask lxd to mount it.
Fits with OpenStack to provide the networking and storage components
Security#
If you are not in a privileged container you won’t be able to create another lxc instance inside that container.
lxc config set myvm2 security.privileged true
lxc config set myvm2 security.nesting true
or with profile:
lxc profile edit customer
- security.nesting -
- security.privileged -