This is the fourth blog post in this series about LXD 2.0.

Available resource limits

LXD offers a variety of resource limits. Some of those are tied to the container itself, like memory quotas, CPU limits and I/O priorities. Some are tied to a particular device instead, like I/O bandwidth or disk usage limits.

As with all LXD configuration, resource limits can be dynamically changed while the container is running. Some may fail to apply, for example if setting a memory value smaller than the current memory usage, but LXD will try anyway and report back on failure.

All limits can also be inherited through profiles in which case each affected container will be constrained by that limit. That is, if you set limits.memory=256MB in the default profile, every container using the default profile (typically all of them) will have a memory limit of 256MB.

We don’t support resource limits pooling where a limit would be shared by a group of containers, there is simply no good way to implement something like that with the existing kernel APIs.

Disk

This is perhaps the most requested and obvious one. Simply setting a size limit on the container’s filesystem and have it enforced against the container.

And that’s exactly what LXD lets you do!
Unfortunately this is far more complicated than it sounds. Linux doesn’t have path-based quotas, instead most filesystems only have user and group quotas which are of little use to containers.

This means that right now LXD only supports disk limits if you’re using the ZFS or btrfs storage backend. It may be possible to implement this feature for LVM too but this depends on the filesystem being used with it and gets tricky when combined with live updates as not all filesystems allow online growth and pretty much none of them allow online shrink.

CPU

When it comes to CPU limits, we support 4 different things:

• Just give me X CPUs
  In this mode, you let LXD pick a bunch of cores for you and then load-balance things as more containers and CPUs go online/offline.
  The container only sees that number of CPU.
• Give me a specific set of CPUs (say, core 1, 3 and 5)
  Similar to the first mode except that no load-balancing is happening, you’re stuck with those cores no matter how busy they may be.
• Give me 20% of whatever you have
  In this mode, you get to see all the CPUs but the scheduler will restrict you to 20% of the CPU time but only when under load! So if the system isn’t busy, your container can have as much fun as it wants. When containers next to it start using the CPU, then it gets capped.
• Out of every measured 200ms, give me 50ms (and no more than that)
  This mode is similar to the previous one in that you get to see all the CPUs but this time, you can only use as much CPU time as you set in the limit, no matter how idle the system may be. On a system without over-commit this lets you slice your CPU very neatly and guarantees constant performance to those containers.

It’s also possible to combine one of the first two with one of the last two, that is, request a set of CPUs and then further restrict how much CPU time you get on those.

On top of that, we also have a generic priority knob which is used to tell the scheduler who wins when you’re under load and two containers are fighting for the same resource.

Memory

Memory sounds pretty simple, just give me X MB of RAM!

And it absolutely can be that simple. We support that kind of limits as well as percentage based requests, just give me 10% of whatever the host has!

Then we support some extra stuff on top. For example, you can choose to turn swap on and off on a per-container basis and if it’s on, set a priority so you can choose what container will have their memory swapped out to disk first!

Oh and memory limits are “hard” by default. That is, when you run out of memory, the kernel out of memory killer will start having some fun with your processes.

Alternatively you can set the enforcement policy to “soft”, in which case you’ll be allowed to use as much memory as you want so long as nothing else is. As soon as something else wants that memory, you won’t be able to allocate anything until you’re back under your limit or until the host has memory to spare again.

Network I/O

Network I/O is probably our simplest looking limit, trust me, the implementation really isn’t simple though!

We support two things. The first is a basic bit/s limits on network interfaces. You can set a limit of ingress and egress or just set the “max” limit which then applies to both. This is only supported for “bridged” and “p2p” type interfaces.

The second thing is a global network I/O priority which only applies when the network interface you’re trying to talk through is saturated.

Block I/O

I kept the weirdest for last. It may look straightforward and feel like that to the user but there are a bunch of cases where it won’t exactly do what you think it should.

What we support here is basically identical to what I described in Network I/O.

You can set IOps or byte/s read and write limits directly on a disk device entry and there is a global block I/O priority which tells the I/O scheduler who to prefer.

The weirdness comes from how and where those limits are applied. Unfortunately the underlying feature we use to implement those uses full block devices. That means we can’t set per-partition I/O limits let alone per-path.

It also means that when using ZFS or btrfs which can use multiple block devices to back a given path (with or without RAID), we effectively don’t know what block device is providing a given path.

This means that it’s entirely possible, in fact likely, that a container may have multiple disk entries (bind-mounts or straight mounts) which are coming from the same underlying disk.

And that’s where things get weird. To make things work, LXD has logic to guess what block devices back a given path, this does include interrogating the ZFS and btrfs tools and even figures things out recursively when it finds a loop mounted file backing a filesystem.

That logic while not perfect, usually yields a set of block devices that should have a limit applied. LXD then records that and moves on to the next path. When it’s done looking at all the paths, it gets to the very weird part. It averages the limits you’ve set for every affected block devices and then applies those.

That means that “in average” you’ll be getting the right speed in the container, but it also means that you can’t have a “/fast” and a “/slow” directory both coming from the same physical disk and with differing speed limits. LXD will let you set it up but in the end, they’ll both give you the average of the two values.

How does it all work?

Most of the limits described above are applied through the Linux kernel Cgroups API. That’s with the exception of the network limits which are applied through good old “tc”.

LXD at startup time detects what cgroups are enabled in your kernel and will only apply the limits which your kernel support. Should you be missing some cgroups, a warning will also be printed by the daemon which will then get logged by your init system.

On Ubuntu 16.04, everything is enabled by default with the exception of swap memory accounting which requires you pass the “swapaccount=1” kernel boot parameter.

Applying some limits

All the limits described above are applied directly to the container or to one of its profiles. Container-wide limits are applied with:

lxc config set CONTAINER KEY VALUE

or for a profile:

lxc profile set PROFILE KEY VALUE

while device-specific ones are applied with:

lxc config device set CONTAINER DEVICE KEY VALUE

or for a profile:

lxc profile device set PROFILE DEVICE KEY VALUE

The complete list of valid configuration keys, device types and device keys can be found here.

CPU

To just limit a container to any 2 CPUs, do:

lxc config set my-container limits.cpu 2

To pin to specific CPU cores, say the second and fourth:

lxc config set my-container limits.cpu 1,3

More complex pinning ranges like this works too:

lxc config set my-container limits.cpu 0-3,7-11

The limits are applied live, as can be seen in this example:

stgraber@dakara:~$ lxc exec zerotier -- cat /proc/cpuinfo | grep ^proces
processor : 0
processor : 1
processor : 2
processor : 3
stgraber@dakara:~$ lxc config set zerotier limits.cpu 2
stgraber@dakara:~$ lxc exec zerotier -- cat /proc/cpuinfo | grep ^proces
processor : 0
processor : 1

Note that to avoid utterly confusing userspace, lxcfs arranges the /proc/cpuinfo entries so that there are no gaps.

As with just about everything in LXD, those settings can also be applied in profiles:

stgraber@dakara:~$ lxc exec snappy -- cat /proc/cpuinfo | grep ^proces
processor : 0
processor : 1
processor : 2
processor : 3
stgraber@dakara:~$ lxc profile set default limits.cpu 3
stgraber@dakara:~$ lxc exec snappy -- cat /proc/cpuinfo | grep ^proces
processor : 0
processor : 1
processor : 2

To limit the CPU time of a container to 10% of the total, set the CPU allowance:

lxc config set my-container limits.cpu.allowance 10%

Or to give it a fixed slice of CPU time:

lxc config set my-container limits.cpu.allowance 25ms/200ms

And lastly, to reduce the priority of a container to a minimum:

lxc config set my-container limits.cpu.priority 0

Memory

To apply a straightforward memory limit run:

lxc config set my-container limits.memory 256MB

(The supported suffixes are kB, MB, GB, TB, PB and EB)

To turn swap off for the container (defaults to enabled):

lxc config set my-container limits.memory.swap false

To tell the kernel to swap this container’s memory first:

lxc config set my-container limits.memory.swap.priority 0

And finally if you don’t want hard memory limit enforcement:

lxc config set my-container limits.memory.enforce soft

Disk and block I/O

Unlike CPU and memory, disk and I/O limits are applied to the actual device entry, so you either need to edit the original device or mask it with a more specific one.

To set a disk limit (requires btrfs or ZFS):

lxc config device set my-container root size 20GB

For example:

stgraber@dakara:~$ lxc exec zerotier -- df -h /
Filesystem                        Size Used Avail Use% Mounted on
encrypted/lxd/containers/zerotier 179G 542M  178G   1% /
stgraber@dakara:~$ lxc config device set zerotier root size 20GB
stgraber@dakara:~$ lxc exec zerotier -- df -h /
Filesystem                       Size  Used Avail Use% Mounted on
encrypted/lxd/containers/zerotier 20G  542M   20G   3% /

To restrict speed you can do the following:

lxc config device set my-container root limits.read 30MB
lxc config device set my-container root.limits.write 10MB

Or to restrict IOps instead:

lxc config device set my-container root limits.read 20iops
lxc config device set my-container root limits.write 10iops

And lastly, if you’re on a busy system with over-commit, you may want to also do:

lxc config set my-container limits.disk.priority 10

To increase the I/O priority for that container to the maximum.

Network I/O

Network I/O is basically identical to block I/O as far the knobs available.

For example:

stgraber@dakara:~$ lxc exec zerotier -- wget http://speedtest.newark.linode.com/100MB-newark.bin -O /dev/null
--2016-03-26 22:17:34-- http://speedtest.newark.linode.com/100MB-newark.bin
Resolving speedtest.newark.linode.com (speedtest.newark.linode.com)... 50.116.57.237, 2600:3c03::4b
Connecting to speedtest.newark.linode.com (speedtest.newark.linode.com)|50.116.57.237|:80... connected.
HTTP request sent, awaiting response... 200 OK
Length: 104857600 (100M) [application/octet-stream]
Saving to: '/dev/null'

/dev/null 100%[===================>] 100.00M 58.7MB/s in 1.7s 

2016-03-26 22:17:36 (58.7 MB/s) - '/dev/null' saved [104857600/104857600]

stgraber@dakara:~$ lxc profile device set default eth0 limits.ingress 100Mbit
stgraber@dakara:~$ lxc profile device set default eth0 limits.egress 100Mbit
stgraber@dakara:~$ lxc exec zerotier -- wget http://speedtest.newark.linode.com/100MB-newark.bin -O /dev/null
--2016-03-26 22:17:47-- http://speedtest.newark.linode.com/100MB-newark.bin
Resolving speedtest.newark.linode.com (speedtest.newark.linode.com)... 50.116.57.237, 2600:3c03::4b
Connecting to speedtest.newark.linode.com (speedtest.newark.linode.com)|50.116.57.237|:80... connected.
HTTP request sent, awaiting response... 200 OK
Length: 104857600 (100M) [application/octet-stream]
Saving to: '/dev/null'

/dev/null 100%[===================>] 100.00M 11.4MB/s in 8.8s 

2016-03-26 22:17:56 (11.4 MB/s) - '/dev/null' saved [104857600/104857600]

And that’s how you throttle an otherwise nice gigabit connection to a mere 100Mbit/s one!

And as with block I/O, you can set an overall network priority with:

lxc config set my-container limits.network.priority 5

Getting the current resource usage

The LXD API exports quite a bit of information on current container resource usage, you can get:

• Memory: current, peak, current swap and peak swap
• Disk: current disk usage
• Network: bytes and packets received and transferred for every interface

And now if you’re running a very recent LXD (only in git at the time of this writing), you can also get all of those in “lxc info”:

stgraber@dakara:~$ lxc info zerotier
Name: zerotier
Architecture: x86_64
Created: 2016/02/20 20:01 UTC
Status: Running
Type: persistent
Profiles: default
Pid: 29258
Ips:
 eth0: inet 172.17.0.101
 eth0: inet6 2607:f2c0:f00f:2700:216:3eff:feec:65a8
 eth0: inet6 fe80::216:3eff:feec:65a8
 lo: inet 127.0.0.1
 lo: inet6 ::1
 lxcbr0: inet 10.0.3.1
 lxcbr0: inet6 fe80::f0bd:55ff:feee:97a2
 zt0: inet 29.17.181.59
 zt0: inet6 fd80:56c2:e21c:0:199:9379:e711:b3e1
 zt0: inet6 fe80::79:e7ff:fe0d:5123
Resources:
 Processes: 33
 Disk usage:
  root: 808.07MB
 Memory usage:
  Memory (current): 106.79MB
  Memory (peak): 195.51MB
  Swap (current): 124.00kB
  Swap (peak): 124.00kB
 Network usage:
  lxcbr0:
   Bytes received: 0 bytes
   Bytes sent: 570 bytes
   Packets received: 0
   Packets sent: 0
  zt0:
   Bytes received: 1.10MB
   Bytes sent: 806 bytes
   Packets received: 10957
   Packets sent: 10957
  eth0:
   Bytes received: 99.35MB
   Bytes sent: 5.88MB
   Packets received: 64481
   Packets sent: 64481
  lo:
   Bytes received: 9.57kB
   Bytes sent: 9.57kB
   Packets received: 81
   Packets sent: 81
Snapshots:
 zerotier/blah (taken at 2016/03/08 23:55 UTC) (stateless)

Conclusion

The LXD team spent quite a few months iterating over the language we’re using for those limits. It’s meant to be as simple as it can get while remaining very powerful and specific when you want it to.

Live application of those limits and inheritance through profiles makes it a very powerful tool to live manage the load on your servers without impacting the running services.

Extra information

The main LXD website is at: https://linuxcontainers.org/lxd
Development happens on Github at: https://github.com/lxc/lxd
Mailing-list support happens on: https://lists.linuxcontainers.org
IRC support happens in: #lxcontainers on irc.freenode.net

And if you don’t want or can’t install LXD on your own machine, you can always try it online instead!

This is the third blog post in this series about LXD 2.0.

As there are a lot of commands involved with managing LXD containers, this post is rather long. If you’d instead prefer a quick step-by-step tour of those same commands, you can try our online demo instead!

Creating and starting a new container

As I mentioned in the previous posts, the LXD command line client comes pre-configured with a few image sources. Ubuntu is the best covered with official images for all its releases and architectures but there also are a number of unofficial images for other distributions. Those are community generated and maintained by LXC upstream contributors.

Ubuntu

If all you want is the best supported release of Ubuntu, all you have to do is:

lxc launch ubuntu:

Note however that the meaning of this will change as new Ubuntu LTS releases are released. So for scripting use, you should stick to mentioning the actual release you want (see below).

Ubuntu 14.04 LTS

To get the latest, tested, stable image of Ubuntu 14.04 LTS, you can simply run:

lxc launch ubuntu:14.04

In this mode, a random container name will be picked.
If you prefer to specify your own name, you may instead do:

lxc launch ubuntu:14.04 c1

Should you want a specific (non-primary) architecture, say a 32bit Intel image, you can do:

lxc launch ubuntu:14.04/i386 c2

Current Ubuntu development release

The “ubuntu:” remote used above only provides official, tested images for Ubuntu. If you instead want untested daily builds, as is appropriate for the development release, you’ll want to use the “ubuntu-daily:” remote instead.

lxc launch ubuntu-daily:devel c3

In this example, whatever the latest Ubuntu development release is will automatically be picked.

You can also be explicit, for example by using the code name:

lxc launch ubuntu-daily:xenial c4

Latest Alpine Linux

Alpine images are available on the “images:” remote and can be launched with:

lxc launch images:alpine/3.3/amd64 c5

And many more

A full list of the Ubuntu images can be obtained with:

lxc image list ubuntu:
lxc image list ubuntu-daily:

And of all the unofficial images:

lxc image list images:

A list of all the aliases (friendly names) available on a given remote can also be obtained with (for the “ubuntu:” remote):

lxc image alias list ubuntu:

Creating a container without starting it

If you want to just create a container or a batch of container but not also start them immediately, you can just replace “lxc launch” by “lxc init”. All the options are identical, the only different is that it will not start the container for you after creation.

lxc init ubuntu:

Information about your containers

Listing the containers

To list all your containers, you can do:

lxc list

There are a number of options you can pass to change what columns are displayed. On systems with a lot of containers, the default columns can be a bit slow (due to having to retrieve network information from the containers), you may instead want:

lxc list --fast

Which shows a different set of columns that require less processing on the server side.

You can also filter based on name or properties:

stgraber@dakara:~$ lxc list security.privileged=true
+------+---------+---------------------+-----------------------------------------------+------------+-----------+
| NAME |  STATE  |        IPV4         |                       IPV6                    |    TYPE    | SNAPSHOTS |
+------+---------+---------------------+-----------------------------------------------+------------+-----------+
| suse | RUNNING | 172.17.0.105 (eth0) | 2607:f2c0:f00f:2700:216:3eff:fef2:aff4 (eth0) | PERSISTENT | 0         |
+------+---------+---------------------+-----------------------------------------------+------------+-----------+

In this example, only containers that are privileged (user namespace disabled) are listed.

stgraber@dakara:~$ lxc list --fast alpine
+-------------+---------+--------------+----------------------+----------+------------+
|    NAME     |  STATE  | ARCHITECTURE |      CREATED AT      | PROFILES |    TYPE    |
+-------------+---------+--------------+----------------------+----------+------------+
| alpine      | RUNNING | x86_64       | 2016/03/20 02:11 UTC | default  | PERSISTENT |
+-------------+---------+--------------+----------------------+----------+------------+
| alpine-edge | RUNNING | x86_64       | 2016/03/20 02:19 UTC | default  | PERSISTENT |
+-------------+---------+--------------+----------------------+----------+------------+

And in this example, only the containers which have “alpine” in their names (complex regular expressions are also supported).

Getting detailed information from a container

As the list command obviously can’t show you everything about a container in a nicely readable way, you can query information about an individual container with:

lxc info <container>

For example:

stgraber@dakara:~$ lxc info zerotier
Name: zerotier
Architecture: x86_64
Created: 2016/02/20 20:01 UTC
Status: Running
Type: persistent
Profiles: default
Pid: 31715
Processes: 32
Ips:
 eth0: inet 172.17.0.101
 eth0: inet6 2607:f2c0:f00f:2700:216:3eff:feec:65a8
 eth0: inet6 fe80::216:3eff:feec:65a8
 lo: inet 127.0.0.1
 lo: inet6 ::1
 lxcbr0: inet 10.0.3.1
 lxcbr0: inet6 fe80::c0a4:ceff:fe52:4d51
 zt0: inet 29.17.181.59
 zt0: inet6 fd80:56c2:e21c:0:199:9379:e711:b3e1
 zt0: inet6 fe80::79:e7ff:fe0d:5123
Snapshots:
 zerotier/blah (taken at 2016/03/08 23:55 UTC) (stateless)

Life-cycle management commands

Those are probably the most obvious commands of any container or virtual machine manager but they still need to be covered.

Oh and all of them accept multiple container names for batch operation.

start

Starting a container is as simple as:

lxc start <container>

stop

Stopping a container can be done with:

lxc stop <container>

If the container isn’t cooperating (not responding to SIGPWR), you can force it with:

lxc stop <container> --force

restart

Restarting a container is done through:

lxc restart <container>

And if not cooperating (not responding to SIGINT), you can force it with:

lxc restart <container> --force

pause

You can also “pause” a container. In this mode, all the container tasks will be sent the equivalent of a SIGSTOP which means that they will still be visible and will still be using memory but they won’t get any CPU time from the scheduler.

This is useful if you have a CPU hungry container that takes quite a while to start but that you aren’t constantly using. You can let it start, then pause it, then start it again when needed.

lxc pause <container>

delete

Lastly, if you want a container to go away, you can delete it for good with:

lxc delete <container>

Note that you will have to pass “–force” if the container is currently running.

Container configuration

LXD exposes quite a few container settings, including resource limitation, control of container startup and a variety of device pass-through options. The full list is far too long to cover in this post but it’s available here.

As far as devices go, LXD currently supports the following device types:

• disk
  This can be a physical disk or partition being mounted into the container or a bind-mounted path from the host.
• nic
  A network interface. It can be a bridged virtual ethernet interrface, a point to point device, an ethernet macvlan device or an actual physical interface being passed through to the container.
• unix-block
  A UNIX block device, e.g. /dev/sda
• unix-char
  A UNIX character device, e.g. /dev/kvm
• none
  This special type is used to hide a device which would otherwise be inherited through profiles.

Configuration profiles

The list of all available profiles can be obtained with:

lxc profile list

To see the content of a given profile, the easiest is to use:

lxc profile show <profile>

And should you want to change anything inside it, use:

lxc profile edit <profile>

You can change the list of profiles which apply to a given container with:

lxc profile apply <container> <profile1>,<profile2>,<profile3>,...

Local configuration

For things that are unique to a container and so don’t make sense to put into a profile, you can just set them directly against the container:

lxc config edit <container>

This behaves the exact same way as “profile edit” above.

Instead of opening the whole thing in a text editor, you can also modify individual keys with:

lxc config set <container> <key> <value>

Or add devices, for example:

lxc config device add my-container kvm unix-char path=/dev/kvm

Which will setup a /dev/kvm entry for the container named “my-container”.

The same can be done for a profile using “lxc profile set” and “lxc profile device add”.

Reading the configuration

You can read the container local configuration with:

lxc config show <container>

Or to get the expanded configuration (including all the profile keys):

lxc config show --expanded <container>

For example:

stgraber@dakara:~$ lxc config show --expanded zerotier
name: zerotier
profiles:
- default
config:
 security.nesting: "true"
 user.a: b
 volatile.base_image: a49d26ce5808075f5175bf31f5cb90561f5023dcd408da8ac5e834096d46b2d8
 volatile.eth0.hwaddr: 00:16:3e:ec:65:a8
 volatile.last_state.idmap: '[{"Isuid":true,"Isgid":false,"Hostid":100000,"Nsid":0,"Maprange":65536},{"Isuid":false,"Isgid":true,"Hostid":100000,"Nsid":0,"Maprange":65536}]'
devices:
 eth0:
  name: eth0
  nictype: macvlan
  parent: eth0
  type: nic
  limits.ingress: 10Mbit
  limits.egress: 10Mbit
 root:
  path: /
  size: 30GB
  type: disk
 tun:
  path: /dev/net/tun
  type: unix-char
ephemeral: false

That one is very convenient to check what will actually be applied to a given container.

Live configuration update

Note that unless indicated in the documentation, all configuration keys and device entries are applied to affected containers live. This means that you can add and remove devices or alter the security profile of running containers without ever having to restart them.

Getting a shell

LXD lets you execute tasks directly into the container. The most common use of this is to get a shell in the container or to run some admin tasks.

The benefit of this compared to SSH is that you’re not dependent on the container being reachable over the network or on any software or configuration being present inside the container.

Execution environment

One thing that’s a bit unusual with the way LXD executes commands inside the container is that it’s not itself running inside the container, which means that it can’t know what shell to use, what environment variables to set or what path to use for your home directory.

Commands executed through LXD will always run as the container’s root user (uid 0, gid 0) with a minimal PATH environment variable set and a HOME environment variable set to /root.

Additional environment variables can be passed through the command line or can be set permanently against the container through the “environment.<key>”  configuration options.

Executing commands

Getting a shell inside a container is typically as simple as:

lxc exec <container> bash

That’s assuming the container does actually have bash installed.

More complex commands require the use of a separator for proper argument parsing:

lxc exec <container> -- ls -lh /

To set or override environment variables, you can use the “–env” argument, for example:

stgraber@dakara:~$ lxc exec zerotier --env mykey=myvalue env | grep mykey
mykey=myvalue

Managing files

Because LXD has direct access to the container’s file system, it can directly read and write any file inside the container. This can be very useful to pull log files or exchange files with the container.

Pulling a file from the container

To get a file from the container, simply run:

lxc file pull <container>/<path> <dest>

For example:

stgraber@dakara:~$ lxc file pull zerotier/etc/hosts hosts

Or to read it to standard output:

stgraber@dakara:~$ lxc file pull zerotier/etc/hosts -
127.0.0.1 localhost

# The following lines are desirable for IPv6 capable hosts
::1 ip6-localhost ip6-loopback
fe00::0 ip6-localnet
ff00::0 ip6-mcastprefix
ff02::1 ip6-allnodes
ff02::2 ip6-allrouters
ff02::3 ip6-allhosts

Pushing a file to the container

Push simply works the other way:

lxc file push <source> <container>/<path>

Editing a file directly

Edit is a convenience function which simply pulls a given path, opens it in your default text editor and then pushes it back to the container when you close it:

lxc file edit <container>/<path>

Snapshot management

LXD lets you snapshot and restore containers. Snapshots include the entirety of the container’s state (including running state if –stateful is used), which means all container configuration, container devices and the container file system.

Creating a snapshot

You can snapshot a container with:

lxc snapshot <container>

It’ll get named snapX where X is an incrementing number.

Alternatively, you can name your snapshot with:

lxc snapshot <container> <snapshot name>

Listing snapshots

The number of snapshots a container has is listed in “lxc list”, but the actual snapshot list is only visible in “lxc info”.

lxc info <container>

Restoring a snapshot

To restore a snapshot, simply run:

lxc restore <container> <snapshot name>

Renaming a snapshot

Renaming a snapshot can be done by moving it with:

lxc move <container>/<snapshot name> <container>/<new snapshot name>

Creating a new container from a snapshot

You can create a new container which will be identical to another container’s snapshot except for the volatile information being reset (MAC address):

lxc copy <source container>/<snapshot name> <destination container>

Deleting a snapshot

And finally, to delete a snapshot, just run:

lxc delete <container>/<snapshot name>

Cloning and renaming

Getting clean distribution images is all nice and well, but sometimes you want to install a bunch of things into your container, configure it and then branch it into a bunch of other containers.

Copying a container

To copy a container and effectively clone it into a new one, just run:

lxc copy <source container> <destination container>

The destination container will be identical in every way to the source one, except it won’t have any snapshot and volatile keys (MAC address) will be reset.

Moving a container

LXD lets you copy and move containers between hosts, but that will get covered in a later post.

For now, the “move” command can be used to rename a container with:

lxc move <old name> <new name>

The only requirement is that the container be stopped, everything else will be kept exactly as it was, including the volatile information (MAC address and such).

Conclusion

This pretty long post covered most of the commands you’re likely to use in day to day operation.

Obviously a lot of those commands have extra arguments that let you be more efficient or tweak specific aspects of your LXD containers. The best way to learn about all of those is to go through the help for those you care about (–help).

Extra information

The main LXD website is at: https://linuxcontainers.org/lxd
Development happens on Github at: https://github.com/lxc/lxd
Mailing-list support happens on: https://lists.linuxcontainers.org
IRC support happens in: #lxcontainers on irc.freenode.net

And if you don’t want or can’t install LXD on your own machine, you can always try it online instead!

This is the second blog post in this series about LXD 2.0.

Where to get LXD and how to install it

There are many ways to get the latest and greatest LXD. We recommend you use LXD with the latest LXC and Linux kernel to benefit from all its features but we try to degrade gracefully where possible to support older Linux distributions.

The Ubuntu archive

All new releases of LXD get uploaded to the Ubuntu development release within a few minutes of the upstream release. That package is then used to seed all the other source of packages for Ubuntu users.

If you are using the Ubuntu development release (16.04), you can simply do:

sudo apt install lxd

If you are running Ubuntu 14.04, we have backport packages available for you with:

sudo apt -t trusty-backports install lxd

The Ubuntu Core store

Users of Ubuntu Core on the stable release can install LXD with:

sudo snappy install lxd.stgraber

The official Ubuntu PPA

Users of other Ubuntu releases such as Ubuntu 15.10 can find LXD packages in the following PPA (Personal Package Archive):

sudo apt-add-repository ppa:ubuntu-lxc/stable
sudo apt update
sudo apt dist-upgrade
sudo apt install lxd

The Gentoo archive

Gentoo has pretty recent LXD packages available too, you can install those with:

sudo emerge --ask lxd

From source

Building LXD from source isn’t very difficult if you are used to building Go projects. Note however that you will need the LXC development headers. In order to run LXD, your distribution also needs a recent Linux kernel (3.13 at least), recent LXC (1.1.5 or higher), LXCFS and a version of shadow that supports user sub-uid/gid allocations.

The latest instructions on building LXD from source can be found in the upstream README.

Networking on Ubuntu

The Ubuntu packages provide you with a “lxdbr0” bridge as a convenience. This bridge comes unconfigured by default, offering only IPv6 link-local connectivity through an HTTP proxy.

To reconfigure the bridge and add some IPv4 or IPv6 subnet to it, you can run:

sudo dpkg-reconfigure -p medium lxd

Or go through the whole LXD step by step setup (see below) with:

sudo lxd init

Storage backends

LXD supports a number of storage backends. It’s best to know what backend you want to use prior to starting to use LXD as we do not support moving existing containers or images between backends.

A feature comparison table of the different backends can be found here.

ZFS

Our recommendation is ZFS as it supports all the features LXD needs to offer the fastest and most reliable container experience. This includes per-container disk quotas, immediate snapshot/restore, optimized migration (send/receive) and instant container creation from an image. It is also considered more mature than btrfs.

To use ZFS with LXD, you first need ZFS on your system.

If using Ubuntu 16.04, simply install it with:

sudo apt install zfsutils-linux

On Ubuntu 15.10, you can install it with:

sudo apt install zfsutils-linux zfs-dkms

And on older releases, you can use the zfsonlinux PPA:

sudo apt-add-repository ppa:zfs-native/stable
sudo apt update
sudo apt install ubuntu-zfs

To configure LXD to use it, simply run:

sudo lxd init

This will ask you a few questions about what kind of zfs configuration you’d like for your LXD and then configure it for you.

btrfs

If ZFS isn’t available, then btrfs offers the same level of integration with the exception that it doesn’t properly report disk usage inside the container (quotas do apply though).
btrfs also has the nice property that it can nest properly which ZFS doesn’t yet. That is, if you plan on using LXD inside LXD, btrfs is worth considering.

LXD doesn’t need any configuration to use btrfs, you just need to make sure that /var/lib/lxd is stored on a btrfs filesystem and LXD will automatically make use of it for you.

LVM

If ZFS and btrfs aren’t an option for you, you can still get some of their benefits by using LVM instead. LXD uses LVM with thin provisioning, creating an LV for each image and container and using LVM snapshots as needed.

To configure LXD to use LVM, create a LVM VG and run:

lxc config set storage.lvm_vg_name "THE-NAME-OF-YOUR-VG"

By default LXD uses ext4 as the filesystem for all the LVs. You can change that to XFS if you’d like:

lxc config set storage.lvm_fstype xfs

Simple directory

If none of the above are an option for you, LXD will still work but without any of those advanced features. It will simply create a directory for each container, unpack the image tarballs for each container creation and do a full filesystem copy on container copy or snapshot.

All features are supported except for disk quotas, but this is very wasteful of disk space and also very slow. If you have no other choice, it will work, but you should really consider one of the alternatives above.

 

More daemon configuration

The complete list of configuration options for the LXD daemon can be found here.

Network configuration

By default LXD doesn’t listen to the network. The only way to talk to it is over a local unix socket at /var/lib/lxd/unix.socket.

To have it listen to the network, there are two useful keys to set:

lxc config set core.https_address [::]
lxc config set core.trust_password some-secret-string

The first instructs LXD to bind the “::” IPv6 address, namely, all addresses on the machine. You can obviously replace this by a specific IPv4 or IPv6 address and can append the TCP port you’d like it to bind (defaults to 8443).

The second sets a password which is used for remote clients to add themselves to the LXD certificate trust store. When adding the LXD host, they will be prompted for the password, if the password matches, the LXD daemon will store their client certificate and they’ll be trusted, never needing the password again (it can be changed or unset entirely at that point).

You can also choose not to set a password and instead manually trust each new client by having them give you their “client.crt” file (from ~/.config/lxc) and add it to the trust store yourself with:

lxc config trust add client.crt

Proxy configuration

In most setups, you’ll want the LXD daemon to fetch images from remote servers.

If you are in an environment where you must go through a HTTP(s) proxy to reach the outside world, you’ll want to set a few configuration keys or alternatively make sure that the standard PROXY environment variables are set in the daemon’s environment.

lxc config set core.proxy_http http://squid01.internal:3128
lxc config set core.proxy_https http://squid01.internal:3128
lxc config set core.proxy_ignore_hosts image-server.local

With those, all transfers initiated by LXD will use the squid01.internal HTTP proxy, except for traffic to the server at image-server.local

Image management

LXD does dynamic image caching. When instructed to create a container from a remote image, it will download that image into its image store, mark it as cached and record its origin. After a number of days without seeing any use (10 by default), the image is automatically removed. Every few hours (6 by default), LXD also goes looking for a newer version of the image and updates its local copy.

All of that can be configured through the following configuration options:

lxc config set images.remote_cache_expiry 5
lxc config set images.auto_update_interval 24
lxc config set images.auto_update_cached false

Here we are instructing LXD to override all of those defaults and instead cache images for up to 5 days since they were last used, look for image updates every 24 hours and only update images which were directly marked as such (–auto-update flag in lxc image copy) but not the images which were automatically cached by LXD.

Conclusion

At this point you should have a working version of the latest LXD release, you can now start playing with it on your own or wait for the next blog post where we’ll create our first container and play with the LXD command line tool.

Extra information

The main LXD website is at: https://linuxcontainers.org/lxd
Development happens on Github at: https://github.com/lxc/lxd
Mailing-list support happens on: https://lists.linuxcontainers.org
IRC support happens in: #lxcontainers on irc.freenode.net

And if you can’t wait until the next few posts to try LXD, you can take our guided tour online and try it for free right from your web browser!

This is the first blog post in this series about LXD 2.0.

A few common questions about LXD

What’s LXD?

At its simplest, LXD is a daemon which provides a REST API to drive LXC containers.

Its main goal is to provide a user experience that’s similar to that of virtual machines but using Linux containers rather than hardware virtualization.

 

How does LXD relate to Docker/Rkt?

This is by far the question we get the most, so lets address it immediately!

LXD focuses on system containers, also called infrastructure containers. That is, a LXD container runs a full Linux system, exactly as it would be when run on metal or in a VM.

Those containers will typically be long running and based on a clean distribution image. Traditional configuration management tools and deployment tools can be used with LXD containers exactly as you would use them for a VM, cloud instance or physical machine.

In contrast, Docker focuses on ephemeral, stateless, minimal containers that won’t typically get upgraded or re-configured but instead just be replaced entirely. That makes Docker and similar projects much closer to a software distribution mechanism than a machine management tool.

The two models aren’t mutually exclusive either. You can absolutely use LXD to provide full Linux systems to your users who can then install Docker inside their LXD container to run the software they want.

Why LXD?

We’ve been working on LXC for a number of years now. LXC is great at what it does, that is, it provides a very good set of low-level tools and a library to create and manage containers.

However that kind of low-level tools aren’t necessarily very user friendly. They require a lot of initial knowledge to understand what they do and how they work. Keeping backward compatibility with older containers and deployment methods has also prevented LXC from using some security features by default, leading to more manual configuration for users.

We see LXD as the opportunity to address those shortcomings. On top of being a long running daemon which lets us address a lot of the LXC limitations like dynamic resource restrictions, container migration and efficient live migration, it also gave us the opportunity to come up with a new default experience, that’s safe by default and much more user focused.

The main LXD components

There are a number of main components that make LXD, those are typically visible in the LXD directory structure, in its command line client and in the API structure itself.

Containers

Containers in LXD are made of:

• A filesystem (rootfs)
• A list of configuration options, including resource limits, environment, security options and more
• A bunch of devices like disks, character/block unix devices and network interfaces
• A set of profiles the container inherits configuration from (see below)
• Some properties (container architecture, ephemeral or persistent and the name)
• Some runtime state (when using CRIU for checkpoint/restore)

Snapshots

Container snapshots are identical to containers except for the fact that they are immutable, they can be renamed, destroyed or restored but cannot be modified in any way.

It is worth noting that because we allow storing the container runtime state, this effectively gives us the concept of “stateful” snapshots. That is, the ability to rollback the container including its cpu and memory state at the time of the snapshot.

Images

LXD is image based, all LXD containers come from an image. Images are typically clean Linux distribution images similar to what you would use for a virtual machine or cloud instance.

It is possible to “publish” a container, making an image from it which can then be used by the local or remote LXD hosts.

Images are uniquely identified by their sha256 hash and can be referenced by using their full or partial hash. Because typing long hashes isn’t particularly user friendly, images can also have any number of properties applied to them, allowing for an easy search through the image store. Aliases can also be set as a one to one mapping between a unique user friendly string and an image hash.

LXD comes pre-configured with three remote image servers (see remotes below):

• “ubuntu:” provides stable Ubuntu images
• “ubunt-daily:” provides daily builds of Ubuntu
• “images:” is a community run image server providing images for a number of other Linux distributions using the upstream LXC templates

Remote images are automatically cached by the LXD daemon and kept for a number of days (10 by default) since they were last used before getting expired.

Additionally LXD also automatically updates remote images (unless told otherwise) so that the freshest version of the image is always available locally.

Profiles

Profiles are a way to define container configuration and container devices in one place and then have it apply to any number of containers.

A container can have multiple profiles applied to it. When building the final container configuration (known as expanded configuration), the profiles will be applied in the order they were defined in, overriding each other when the same configuration key or device is found. Then the local container configuration is applied on top of that, overriding anything that came from a profile.

LXD ships with two pre-configured profiles:

• “default” is automatically applied to all containers unless an alternative list of profiles is provided by the user. This profile currently does just one thing, define a “eth0” network device for the container.
• “docker” is a profile you can apply to a container which you want to allow to run Docker containers. It requests LXD load some required kernel modules, turns on container nesting and sets up a few device entries.

Remotes

As I mentioned earlier, LXD is a networked daemon. The command line client that comes with it can therefore talk to multiple remote LXD servers as well as image servers.

By default, our command line client comes with the following remotes defined

• local: (default remote, talks to the local LXD daemon over a unix socket)
• ubuntu: (Ubuntu image server providing stable builds)
• ubuntu-daily: (Ubuntu image server providing daily builds)
• images: (images.linuxcontainers.org image server)

Any combination of those remotes can be used with the command line client.

You can also add any number of remote LXD hosts that were configured to listen to the network. Either anonymously if they are a public image server or after going through authentication when managing remote containers.

It’s that remote mechanism that makes it possible to interact with remote image servers as well as copy or move containers between hosts.

Security

One aspect that was core to our design of LXD was to make it as safe as possible while allowing modern Linux distributions to run inside it unmodified.

The main security features used by LXD through its use of the LXC library are:

• Kernel namespaces. Especially the user namespace as a way to keep everything the container does separate from the rest of the system. LXD uses the user namespace by default (contrary to LXC) and allows for the user to turn it off on a per-container basis (marking the container “privileged”) when absolutely needed.
• Seccomp. To filter some potentially dangerous system calls.
• AppArmor: To provide additional restrictions on mounts, socket, ptrace and file access. Specifically restricting cross-container communication.
• Capabilities. To prevent the container from loading kernel modules, altering the host system time, …
• CGroups. To restrict resource usage and prevent DoS attacks against the host.

Rather than exposing those features directly to the user as LXC would, we’ve built a new configuration language which abstracts most of those into something that’s more user friendly. For example, one can tell LXD to pass any host device into the container without having to also lookup its major/minor numbers to manually update the cgroup policy.

Communications with LXD itself are secured using TLS 1.2 with a very limited set of allowed ciphers. When dealing with hosts outside of the system certificate authority, LXD will prompt the user to validate the remote fingerprint (SSH style), then cache the certificate for future use.

The REST API

Everything that LXD does is done over its REST API. There is no other communication channel between the client and the daemon.

The REST API can be access over a local unix socket, only requiring group membership for authentication or over a HTTPs socket using a client certificate for authentication.

The structure of the REST API matches the different components described above and is meant to be very simple and intuitive to use.

When a more complex communication mechanism is required, LXD will negotiate websockets and use those for the rest of the communication. This is used for interactive console session, container migration and for event notification.

With LXD 2.0, comes the /1.0 stable API. We will not break backward compatibility within the /1.0 API endpoint however we may add extra features to it, which we’ll signal by declaring additional API extensions that the client can look for.

Containers at scale

While LXD provides a good command line client, that client isn’t meant to manage thousands of containers on multiple hosts. For that kind of use cases, we have nova-lxd which is an OpenStack plugin that makes OpenStack treat LXD containers in the exact same way it would treat VMs.

This allows for very large deployments of LXDs on a large number of hosts, using the OpenStack APIs to manage network, storage and load-balancing.

Extra information

The main LXD website is at: https://linuxcontainers.org/lxd
Development happens on Github at: https://github.com/lxc/lxd
Mailing-list support happens on: https://lists.linuxcontainers.org
IRC support happens in: #lxcontainers on irc.freenode.net

And if you can’t wait until the next few posts to try LXD, you can take our guided tour online and try it for free right from your web browser!

As we are getting closer and closer to tagging the final releases of LXC, LXD and LXCFS 2.0, I figured it would be a good idea to talk a bit about everything that went into LXD since we first started that project a year and a half ago.

This is going to be a blog post series similar to what I’ve done for LXC 1.0 a couple years back.

The topics that will be covered are:

• LXD 2.0: Introduction to LXD [1/12]
• LXD 2.0: Installing and configuring LXD [2/12]
• LXD 2.0: Your first LXD container [3/12]
• LXD 2.0: Resource control [4/12]
• LXD 2.0: Image management [5/12]
• LXD 2.0: Remote hosts and container migration [6/12]
• LXD 2.0: Docker in LXD [7/12]
• LXD 2.0: LXD in LXD [8/12]
• LXD 2.0: Live migration [9/12]
• LXD 2.0: LXD and Juju [10/12]
• LXD 2.0: LXD and OpenStack [11/12]
• LXD 2.0: Debugging and contributing to LXD [12/12]

Related posts:

• LXD 2.0 has been released!
• Directly interacting with the LXD API
• LXD is now available in the Ubuntu Snap Store
• Network management with LXD (2.3+)
• Running snaps in LXD containers
• Running Kubernetes inside LXD
• LXD on Debian (using snapd)
• Ubuntu Core in LXD containers
• LXD client on Windows and MacOS
• Run your own LXD demo server
• NVidia CUDA inside a LXD container
• USB hotplug with LXD containers
• Custom user mappings in LXD containers

I’m hoping to post a couple of those every week for the coming month and a half leading to the Ubuntu 16.04 release.

If you can’t wait for all of those to come out to play with LXD, you can also take the guided tour and play with LXD, online through our online demo page.