Container Management

XenServer includes two new features to enhance deployments of Docker Containers on XenServer

  • Support for CoreOS Linux VMs and configuring Cloud Config Drives

  • Container Management for CoreOS, Debian 8, Ubuntu 14.04, and RHEL/CentOS/OEL 7.0

  • Preview of Container Management for Windows Server Containers on Windows Server 2016 Technology Preview

CoreOS is a minimalist Linux distribution which has become popular for hosting Docker applications. The CoreOS Cloud Config Drive allows the customization of various operating system configuration options. When Container Management is enabled on a VM, XenServer becomes aware of any Docker containers running in the VM.


For information on how to install CoreOS guests, configure Cloud-Config parameters, and manage Docker containers, refer to the XenCenter online Help. Press F1 or click Help.

The Container Management Supplemental Park enables XenServer to query the VMs, interact with Cloud Config Drives, discover application containers, and display these within XenCenter’s Infrastructure view. XenCenter also enables interaction with the containers to allow for start, stop and pause operations, and other monitoring capabilities. Refer to Container Management Supplemental Pack for more information.

What is Docker

Docker is an open platform for developers and system administrators to build, ship, and run distributed applications. A Docker container comprises just the application and its dependencies. It runs as an isolated process in user space on the host operating system, sharing the kernel and base filesystem with other containers. For more information, refer to:


The XenServer Container Management feature complements, but not does replace the Docker ecosystem. Individual Docker Engine instances in the VMs can be managed by one of the many Docker management tools available.

Container Management Supplemental Pack

The Container Management Supplemental Pack provides:

  • Monitoring and Visibility: allows you to see which VMs are in use for Docker hosting, and which containers on the VM are running.

  • Diagnostics: easy access is provided to basic container information such as forwarded network ports, and originating Docker image name. This can help accelerate investigations into problems where either the infrastructure and applications layers maybe impacted.

  • Performance: gives insight into which containers are running on that VM. Depending on the information provided by the operating system, it provides information on the processes and applications running on the container, and the CPU resource consumed.

  • Control Applications: use XenCenter to start, stop, and pause (if supported by the operating system) application containers enabling rapid termination of problematic applications.


XenServer supports installing Supplemental Packs using XenCenter. For information on how to install a supplemental pack using XenCenter refer to the XenCenter Help. If you would prefer to install using the xe CLI, refer to the XenServer Supplemental Packs and the DDK guide.

Managing Docker Containers Using XenCenter

This section contains information on managing your CoreOS VMs using XenCenter. To manage CoreOS VMs, you should:

  1. Install or upgrade your host to XenServer 7.1.

  2. Install the XenCenter shipped with XenServer 7.1.

  3. Install the Container Management Supplemental pack available from the Citrix website.

  4. Create a CoreOS VM and include a config drive for the VM.

    When you create a CoreOS VM in XenCenter, the New VM wizard prompts you to specify cloud-config parameters for your VM. The config drive provides user data for the VM instance. You should create a config drive if you are planning to use XenServer to manage containers running inside the VM.

    By default, XenCenter includes a predefined set of parameters on the Cloud-Config Parameters page. You can modify these parameters based on your requirements. Refer to CoreOS documentation for detailed information about supported configuration parameters.


    Container Management may not work if you do not create a config drive for the VM.

  5. Enable container management for the VM. You can update this setting on the VM’s Properties tab in XenCenter.


If you want to use Ubuntu 14.04, Debian 8, RHEL/CentOS/Oracle Linux 7, Windows Server 2016 TP VMs to manage Docker containers, you should first enable container management using the CLI. Once the container management is enabled on these VMs, you can use XenCenter to perform lifecycle operations such as start, stop, pause, and resume the containers.

Managing Containers on Other Linux Guests

CoreOS VMs that are created with the default Cloud Config Drive configuration are automatically prepared for Container Management and the capability only needs to be enabled. Other Linux guests can be prepared manually. This is supported for Debian 8, Ubuntu 14.04, and RHEL/CentOS/OEL 7.x VMs only.

To manually prepare a Linux guest:

  1. Ensure the VM has XenServer PV Tools installed, and that the VM network is configured as described in Network Requirements and Security.

  2. Install Docker, ncat, and SSHD inside the VM.

    For Ubuntu 14.04: apt-get install nmap openssh-server

    For RHEL/CentOS/OEL 7.x: yum install docker nmap openssh-server

  3. Enable autostart for docker.service:

systemctl enable docker.service

  1. Start docker.service

systemctl start docker.service

A non-root user should be used for container management; add the user to the 'docker' group to provide access to Docker.
  1. Prepare the VM for container management; run the following command on the control domain (dom0) on one of the hosts in the pool:

xscontainer-prepare-vm -v vm-uuid -u username

Where vm-uuid is the VM to be prepared, and username is the username on the VM that the Container Management will use for management access.

The preparation script guides you through the process and automatically enables container management for this VM.

Accessing Docker Container Console and Logs

For Linux VMs, XenCenter enables customers to access the container console and view logs to manage and monitor applications running on Docker containers. To access the container console and logs using XenCenter:

  1. Select the container in the Resources pane.

  2. On the Container General Properties section, click View Console to view the container console. To see the console logs, click View Log. This opens an SSH client on the machine running XenCenter.

  3. When prompted, log into the SSH client using the VM user name and password.


    Customers can automate the authentication process by configuring their public/private SSH keys. See the following section for details.

Automating the Authentication Process (optional)

When accessing the container console and logs, customers are required to enter the login credentials of the VM to authenticate SSH connections. However, customers can automate the authentication process to avoid entering the credentials manually. Follow the instructions below to configure the automatic authentication process:

  1. Generate a public/private key pair.

  2. Add the public SSH key to the user directory on the VM running the container.

    For example, for containers running on a CoreOS VM, the public key should be added to the Cloud-Config Parameters section on the VM’s General tab in XenCenter. For Ubuntu 14.04, RHEL/CentOS/Oracle Linux 7.x, and Debian 8, the public key should be manually added to ~/.ssh/authorized_keys.

  3. Add the private SSH key to the %userprofile% directory on the machine running XenCenter and rename the key as ContainerManagement.ppk.

Managing Windows Server Containers

Windows Server Containers are part of the Windows Server 2016 guest operating system. They allow the encapsulation of Windows applications by isolating processes into their own namespace. XenServer Container Management supports monitoring and managing Windows Server Containers on Windows Server 2016 guest operating systems.


This functionality requires Windows Server 2016 VMs to be configured with one or more static IP addresses for TLS communication, as TLS server certificates will be bound to certain IP addresses.

To prepare Windows Server Containers for Container Management:

  1. Ensure the VM has XenServer PV Tools installed, and that the VM network is configured as described in Network Requirements and Security.

  2. Install Windows Server Container support inside the VM as described in Microsoft Documentation. Windows Server Containers are not HyperV Containers.

  3. Create a file called ‘daemon.json’ in the folder ‘C:\ProgramData\docker\config’ with the contents:

            "hosts": ["tcp://", "npipe://"],
            "tlsverify": true,
            "tlscacert": "C:\\ProgramData\\docker\\certs.d\\ca.pem",
            "tlscert": "C:\\ProgramData\\docker\\certs.d\\server-cert.pem",
            "tlskey": "C:\\ProgramData\\docker\\certs.d\\server-key.pem"
  4. Prepare the VM for container management; run one of the following commands on the control domain (dom0) on one of the hosts in the pool:

    Option 1 (for single-user VMs): Have XenServer generate TLS certificates for this VM.


    This option is only safe where only a single user has access to the VM. The TLS server and client keys will be injected into the VM using a virtual CD, that might be copied by malicious users during the preparation.

    xscontainer-prepare-vm -v vm-uuid -u root --mode tls --generate-certs

    Where vm-uuid is the VM to be prepared. Follow the on-screen instructions to complete the process of preparing Windows Server Containers. It involves interacting with dom0 and the VM.

    Option 2: To configure XenServer with externally generated TLS certificates

    xscontainer-prepare-vm -v vm-uuid -u root --mode tls --client-cert client-cert
        --client-key client-key --ca-cert ca-cert

    Where vm-uuid is the VM to be prepared, client-cert is the TLS client certificate, client-key is the TLS client key, and ca-cert is the CA certificate. This option assumes that Docker is already configured for TLS inside the VM.

Network Requirements and Security


In order for container management to work, it may be necessary to relax security requirements regarding network isolation.

For maximum security of virtualization environments, Citrix recommends that administrators partition the network by isolating XenServer’s management network (with XenServer Control Domain, dom0) from the VMs.

Enabling container management requires a route between these two networks, which increases the risk of malicious VMs attacking the management network (that is, dom0). To mitigate the risk of allowing traffic between VM and the management network, we advise the configuration of firewall rules to only allow trusted sources to initiate a connection between the two networks.

If this recommended network configuration does not match your risk profile, or if you lack the necessary network or firewall expertise to secure this route sufficiently for your specific use-case, Citrix recommends that you do not use this feature in production.

Network Partitioning and Firewalls

As with other VMs, container managed VMs should not be connected directly to XenServer’s management network to provide necessary isolation.

In order for Container Management to work, managed VMs have to be reachable from the XenServer’ s Control Domain (dom0). To monitor containers on Linux-based operating systems, the networking topology and firewalls must allow outbound SSH (Destination TCP port 22) connections from dom0 (the XenServer Management network) to Container Managed VMs (the VM network). To monitor Windows Server Containers - the networking topology and firewalls must allow outbound Docker TLS (Destination TCP port 2376) connections from dom0 (the XenServer Management network) to Container Managed VMs (the VM network).

To mitigate the risk of allowing traffic between VM and the management network, all traffic should pass an external stateful firewall. This firewall must be manually set up and configured by an expert according to your specific business and security requirement.

The following section contains an example configuration:

To secure connections between the networks:

  • Prevent all connections between the XenServer management network (that is including dom0) and the VM network (that is including container managed VMs) either way.

Add exceptions for enabling Container Management:

  • To monitor Linux-based operating system, allow dom0 to have outbound SSH (TCP port 22) connections (both NEW and ESTABLISHED) to Container Managed VMs.

  • To monitor Windows Server containers, allow dom0 to have outbound Docker TLS (TCP port 2376) connections (both NEW and ESTABLISHED) to Container Managed VMs.

  • Allow Container Managed VMs to reply to (ESTABLISHED) SSH or Docker TLS connections initiated by dom0.

Authentication on Linux-based operating systems

XenServer’s Container Management uses a pool-specific 4096-bit private/public RSA-key-pair to authenticate on Container Managed VMs. The private key is stored in the XenServer Control Domain (dom0). The respective public-key is registered in Container Managed VMs during the preparation, either using the Cloud Config Drive or ~user/.ssh/authorized_keys file. As usual with all private/public key-pairs, the private key must be kept securely, as it allows for password-less access to all Container Managed VMs. This includes both currently managed VMs and VMs managed in the past.

XenServer’s Container Management attempts to reach Container Managed VMs through any of the IP addresses advertised by the XenServer PV Tools running inside the VM. After an initial connection, XenServer stores the public key of container managed VMs and validates that the key matches on any subsequent connection. If the network topology cannot ensure that only the Container Managed VM can be contacted through its advertised IP (using IP Source Guard or similar means), Citrix recommends that administrators confirm the SSH hostkey, that the Container Management obtained when making the first connection to the VM.

The key can be accessed using the following command:

xe vm-parm-get-uuid=vm-uuid param-name=other-config  /

Where vm-uuid is the UUID of the VM.

Authentication for Windows Server Containers

XenServer uses SSL or TLS to monitor and control Windows Server Containers. In this instance XenServer acts as the SSL/TLS client, and Windows Server VMs act as the SSL/TLS server. Keys are stored in both Dom0 and the VM.


  • The client key must be kept securely, as it allows for password-less access to Docker on the VM

  • The server key must be kept securely, as it serves to authenticate the monitoring connection to the VM

When XenServer Container Management generates TLS certificates and keys using the –generate-certs option, a temporary CA, server, and client certificates are generated specifically for a certain pool and VM. Certificates use sha256 hash and are valid for up to 2*365 days, after which the preparation should be repeated. The TLS connection is always established using a AES128-SHA cipher.