Update docker_support.md
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Olivier Lambert
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# Docker support
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> This feature is available since 4.10
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Basic container lifecycle is documented [in the Administration section](https://xen-orchestra.com/docs/administration.html#docker-management).
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This category is dedicated on creating VM with Docker support.
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## Prerequisite
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* XenServer 6.5
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* Plugin installation (see below)
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* CoreOS ISO ([download it here](http://stable.release.core-os.net/amd64-usr/current/coreos_production_iso_image.iso)) for CoreOS installations
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* Xen Orchestra 4.10 or newer
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## Docker plugin installation
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This first step is needed until Docker is supported nativly in the XenServer API (XAPI).
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> The plugin should be installed in every hosts, even if they are on the same pool.
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1. SSH on your XenServer
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1. Download the plugin: `wget http://downloadns.citrix.com.edgesuite.net/10343/XenServer-6.5.0-SP1-xscontainer.iso`
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1. Install it: `xe-install-supplemental-pack XenServer-6.5.0-SP1-xscontainer.iso`
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That's it! You are ready for enjoying Docker support!
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## Docker managed VMs
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There is two ways to use the newest exposed Docker features:
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* install a CoreOS VM
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* transform an existing VM in supported Docker VM
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### CoreOS
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[CoreOS](https://coreos.com/) is a Linux distribution with bundled software, like `etcd`, `rkt`, `fleet` etc. The ISO install CD is also using `CloudInit` (which is the interesting thing here).
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#### Create the VM
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First thing first, create a new VM as usual:
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Then, select the "CoreOS" template in the list and name it as you want:
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Select the [CoreOS ISO](http://stable.release.core-os.net/amd64-usr/current/coreos_production_iso_image.iso) as source for the installation:
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You will also notice Cloud Config panel:
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You'll have to uncomment the line:
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`# - ssh-rsa <Your public key>`
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And replace it with your actual SSH public key:
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`- ssh-rsa AAAA....kuGgQ me@mypc`
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The rest of the configuration is identical to any other VM. Just click on "Create VM" and you are done:
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Your VM is now ready. Nothing else to do. You can see it thanks to the ship logo in the main view:
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But also in the VM view, you'll have a Docker panel:
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It's empty, for sure, because you don't have any Docker container running. So now, let's boot the VM, and create some Docker containers!
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You should be able to access the VM with the user `core` and your SSH key (so no password to write!). Oh and the good news: because Xen tools are installed automatically, you already have the IP address displayed in Xen Orchetra:
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So in our example (use the `core` user):
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```
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me@mypc $ ssh core@192.168.100.209
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The authenticity of host '192.168.100.209 (192.168.100.209)' can't be established.
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ED25519 key fingerprint is SHA256:NDOQgOqUm3J2ZsBEMNFCpXE1lTsu4DKqKN6H7YcxS3k.
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Are you sure you want to continue connecting (yes/no)? yes
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Warning: Permanently added '192.168.100.209' (ED25519) to the list of known hosts.
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Last login: Sun Nov 22 21:00:05 2015
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CoreOS stable (607.0.0)
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Update Strategy: No Reboots
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core@core1 ~ $
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```
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You are now connected! Let's make some tests before installing it on the disks.
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```
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core@core1 ~ $ docker run --name hello -d busybox /bin/sh -c "while true; do echo Hello World; sleep 1; done"
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Unable to find image 'busybox:latest' locally
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Pulling repository busybox
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17583c7dd0da: Download complete
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d1592a710ac3: Download complete
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Status: Downloaded newer image for busybox:latest
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150bc05a84971489b2dd5dc99fe0169cdbd23599d6fac55a6a8756a3c6f52853
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```
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Guess what? Check in Xen Orchestra, in the VM view:
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You can now "cycle" this container: stop, pause or reboot it!
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#### CoreOS installation
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Now it works, you can make a persistent installation of your CoreOS VM. In the same SSH terminal used before, just type:
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```
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core@core1 ~ $ sudo coreos-install -d /dev/xvda -o xen -C stable
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```
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You should have this output:
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```
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Downloading the signature for http://stable.release.core-os.net/amd64-usr/607.0.0/coreos_production_xen_image.bin.bz2...
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...
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Downloading, writing and verifying coreos_production_xen_image.bin.bz2...
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Success! CoreOS stable 607.0.0 (xen) is installed on /dev/xvda
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```
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You can reboot the VM and even eject the CoreOS ISO: it will boot as a normal VM now!
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### How it works
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During the VM creation, the XSContainer plugin will create an extra disk: "Automatic Config Drive", with a size of 2MB. This is where the necessary configuration you edited previously (with the SSH key) is passed to the CoreOS VM! In fact, it uses `CloudInit`.
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#### What is CloudInit?
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`CloudInit` is a software created to simplify VM provisioning for Cloud instances: it was originally developed for the Amazon Cloud, but works with all major Cloud ready systems, like OpenStack for example.
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Basically, it reads configuration during the boot, allowing:
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* SSH keys management for newly created VM/instances
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* Root disk filesystem growing
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* User/group management
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* Arbitrary commands execution (system update, custom scripts etc.)
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In our case, it's used by the XSContainer plugin to allow host communication to the Docker daemon running in the VM, thus exposing Docker commands outside it.
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### Existing VMs
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You can also use the XSContainer plugin to "transform" an existing VM into a "Docker" managed one.
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You need to have this installed inside the VM:
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* Docker
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* openssh-server
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* ncat
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For Debian/Ubuntu like distro: `apt-get install docker.io openssh-server nmap`. For RHEL and derived (CentOS...): `yum install docker openssh-server nmap-ncat`.
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To use Docker as non-root, please add the user you want inside the "Docker" group.
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Now, you need to access to your host (Dom0) and use the following command:
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```
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xscontainer-prepare-vm -v <VM_UUID> -u <username>
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```
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> Because "prepare-vm" is not exposed outside the Dom0 (yet?), we can't use Xen Orchestra to give you a one-click solution so far.
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