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204 lines
8.9 KiB
Markdown
204 lines
8.9 KiB
Markdown
Translating By LHRchina
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Ubuntu Core in LXD containers
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============================================================
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### Share or save
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### What’s Ubuntu Core?
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Ubuntu Core is a version of Ubuntu that’s fully transactional and entirely based on snap packages.
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Most of the system is read-only. All installed applications come from snap packages and all updates are done using transactions. Meaning that should anything go wrong at any point during a package or system update, the system will be able to revert to the previous state and report the failure.
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The current release of Ubuntu Core is called series 16 and was released in November 2016.
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Note that on Ubuntu Core systems, only snap packages using confinement can be installed (no “classic” snaps) and that a good number of snaps will not fully work in this environment or will require some manual intervention (creating user and groups, …). Ubuntu Core gets improved on a weekly basis as new releases of snapd and the “core” snap are put out.
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### Requirements
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As far as LXD is concerned, Ubuntu Core is just another Linux distribution. That being said, snapd does require unprivileged FUSE mounts and AppArmor namespacing and stacking, so you will need the following:
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* An up to date Ubuntu system using the official Ubuntu kernel
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* An up to date version of LXD
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### Creating an Ubuntu Core container
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The Ubuntu Core images are currently published on the community image server.
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You can launch a new container with:
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```
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stgraber@dakara:~$ lxc launch images:ubuntu-core/16 ubuntu-core
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Creating ubuntu-core
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Starting ubuntu-core
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```
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The container will take a few seconds to start, first executing a first stage loader that determines what read-only image to use and setup the writable layers. You don’t want to interrupt the container in that stage and “lxc exec” will likely just fail as pretty much nothing is available at that point.
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Seconds later, “lxc list” will show the container IP address, indicating that it’s booted into Ubuntu Core:
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```
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stgraber@dakara:~$ lxc list
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+-------------+---------+----------------------+----------------------------------------------+------------+-----------+
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| NAME | STATE | IPV4 | IPV6 | TYPE | SNAPSHOTS |
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+-------------+---------+----------------------+----------------------------------------------+------------+-----------+
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| ubuntu-core | RUNNING | 10.90.151.104 (eth0) | 2001:470:b368:b2b5:216:3eff:fee1:296f (eth0) | PERSISTENT | 0 |
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+-------------+---------+----------------------+----------------------------------------------+------------+-----------+
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```
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You can then interact with that container the same way you would any other:
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```
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stgraber@dakara:~$ lxc exec ubuntu-core bash
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root@ubuntu-core:~# snap list
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Name Version Rev Developer Notes
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core 16.04.1 394 canonical -
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pc 16.04-0.8 9 canonical -
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pc-kernel 4.4.0-45-4 37 canonical -
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root@ubuntu-core:~#
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```
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### Updating the container
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If you’ve been tracking the development of Ubuntu Core, you’ll know that those versions above are pretty old. That’s because the disk images that are used as the source for the Ubuntu Core LXD images are only refreshed every few months. Ubuntu Core systems will automatically update once a day and then automatically reboot to boot onto the new version (and revert if this fails).
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If you want to immediately force an update, you can do it with:
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```
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stgraber@dakara:~$ lxc exec ubuntu-core bash
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root@ubuntu-core:~# snap refresh
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pc-kernel (stable) 4.4.0-53-1 from 'canonical' upgraded
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core (stable) 16.04.1 from 'canonical' upgraded
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root@ubuntu-core:~# snap version
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snap 2.17
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snapd 2.17
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series 16
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root@ubuntu-core:~#
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```
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And then reboot the system and check the snapd version again:
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```
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root@ubuntu-core:~# reboot
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root@ubuntu-core:~#
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stgraber@dakara:~$ lxc exec ubuntu-core bash
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root@ubuntu-core:~# snap version
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snap 2.21
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snapd 2.21
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series 16
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root@ubuntu-core:~#
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```
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You can get an history of all snapd interactions with
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```
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stgraber@dakara:~$ lxc exec ubuntu-core snap changes
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ID Status Spawn Ready Summary
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1 Done 2017-01-31T05:14:38Z 2017-01-31T05:14:44Z Initialize system state
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2 Done 2017-01-31T05:14:40Z 2017-01-31T05:14:45Z Initialize device
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3 Done 2017-01-31T05:21:30Z 2017-01-31T05:22:45Z Refresh all snaps in the system
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```
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### Installing some snaps
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Let’s start with the simplest snaps of all, the good old Hello World:
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```
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stgraber@dakara:~$ lxc exec ubuntu-core bash
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root@ubuntu-core:~# snap install hello-world
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hello-world 6.3 from 'canonical' installed
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root@ubuntu-core:~# hello-world
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Hello World!
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```
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And then move on to something a bit more useful:
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```
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stgraber@dakara:~$ lxc exec ubuntu-core bash
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root@ubuntu-core:~# snap install nextcloud
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nextcloud 11.0.1snap2 from 'nextcloud' installed
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```
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Then hit your container over HTTP and you’ll get to your newly deployed Nextcloud instance.
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If you feel like testing the latest LXD straight from git, you can do so with:
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```
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stgraber@dakara:~$ lxc config set ubuntu-core security.nesting true
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stgraber@dakara:~$ lxc exec ubuntu-core bash
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root@ubuntu-core:~# snap install lxd --edge
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lxd (edge) git-c6006fb from 'canonical' installed
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root@ubuntu-core:~# lxd init
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Name of the storage backend to use (dir or zfs) [default=dir]:
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We detected that you are running inside an unprivileged container.
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This means that unless you manually configured your host otherwise,
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you will not have enough uid and gid to allocate to your containers.
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LXD can re-use your container's own allocation to avoid the problem.
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Doing so makes your nested containers slightly less safe as they could
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in theory attack their parent container and gain more privileges than
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they otherwise would.
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Would you like to have your containers share their parent's allocation (yes/no) [default=yes]?
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Would you like LXD to be available over the network (yes/no) [default=no]?
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Would you like stale cached images to be updated automatically (yes/no) [default=yes]?
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Would you like to create a new network bridge (yes/no) [default=yes]?
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What should the new bridge be called [default=lxdbr0]?
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What IPv4 address should be used (CIDR subnet notation, “auto” or “none”) [default=auto]?
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What IPv6 address should be used (CIDR subnet notation, “auto” or “none”) [default=auto]?
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LXD has been successfully configured.
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```
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And because container inception never gets old, lets run Ubuntu Core 16 inside Ubuntu Core 16:
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```
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root@ubuntu-core:~# lxc launch images:ubuntu-core/16 nested-core
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Creating nested-core
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Starting nested-core
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root@ubuntu-core:~# lxc list
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+-------------+---------+---------------------+-----------------------------------------------+------------+-----------+
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| NAME | STATE | IPV4 | IPV6 | TYPE | SNAPSHOTS |
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+-------------+---------+---------------------+-----------------------------------------------+------------+-----------+
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| nested-core | RUNNING | 10.71.135.21 (eth0) | fd42:2861:5aad:3842:216:3eff:feaf:e6bd (eth0) | PERSISTENT | 0 |
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+-------------+---------+---------------------+-----------------------------------------------+------------+-----------+
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```
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### Conclusion
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If you ever wanted to try Ubuntu Core, this is a great way to do it. It’s also a great tool for snap authors to make sure their snap is fully self-contained and will work in all environments.
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Ubuntu Core is a great fit for environments where you want to ensure that your system is always up to date and is entirely reproducible. This does come with a number of constraints that may or may not work for you.
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And lastly, a word of warning. Those images are considered as good enough for testing, but aren’t officially supported at this point. We are working towards getting fully supported Ubuntu Core LXD images on the official Ubuntu image server in the near future.
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### Extra information
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The main LXD website is at: [https://linuxcontainers.org/lxd][2] Development happens on Github at: [https://github.com/lxc/lxd][3]
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Mailing-list support happens on: [https://lists.linuxcontainers.org][4]
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IRC support happens in: #lxcontainers on irc.freenode.net
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Try LXD online: [https://linuxcontainers.org/lxd/try-it][5]
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--------------------------------------------------------------------------------
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via: https://insights.ubuntu.com/2017/02/27/ubuntu-core-in-lxd-containers/
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作者：[Stéphane Graber ][a]
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译者：[译者ID](https://github.com/译者ID)
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校对：[校对者ID](https://github.com/校对者ID)
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本文由 [LCTT](https://github.com/LCTT/TranslateProject) 原创编译，[Linux中国](https://linux.cn/) 荣誉推出
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[a]:https://insights.ubuntu.com/author/stgraber/
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[1]:https://insights.ubuntu.com/author/stgraber/
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[2]:https://linuxcontainers.org/lxd
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[3]:https://github.com/lxc/lxd
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[4]:https://lists.linuxcontainers.org/
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[5]:https://linuxcontainers.org/lxd/try-it
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