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Linux Containers (LXC) is a lightweight system virtualization that uses resource isolation instead of the hardware emulation approach used by KVM and Xen. For users who do not require full OS virtualization as provided by KVM and Xen, container technologies such as LXC provide an attractive performant solution for virtualization.

Cloudstack currently does not support containers such as LXC and OpenVZ.

Purpose

This docoument contains the design specification for LXC support in Cloudstack.

Status

Currently in development/testing, see last section below for detailsCode complete, feature has been merged to master branch.

References

Feature Specification

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Each of the different hypervisors currently have their own System VMs. These system VM images are used to run a console proxy, secondary storage, and router VMs.

We will need to create a System VM for LXC. Until this is ready, we can run a second cluster with a KVM/Xen host to provide the System VM functionality.

If we didn't have the System VM for LXC, we would have to consider how to replace the 3 system VMs:

  • Secondary Storage VM: Run this on the management server
  • Console VM: Libvirt 1.0.0 does not support the <graphics> tag for LXC which is used for remote vnc connections.
  • Router VM: Configure the Guest OS directly with network setttings

Development/testing notes

At a high level, you will need to run the management server, the KVM host, and an LXC host. The LXC host has the exact same setup as the KVM host, the only difference is you specify the "lxc" hypervisor in the agent config file. The KVM host is needed for running the System VMs since we do not yet have equivalents for LXC.

I am currently running my dev/test setup on two machines: 1) runs the management + KVM agent and 2) the other runs the LXC agent. The following sections detail how to get the development code running so that you can spin up LXC containers with Cloudstack. It's not very elegant, but is the easiest way I've found to quickly get the system up with development code. There's probably an easier way to do this, like with RPMs, but I haven't gotten around to getting the proper environment up.

1. Install Cloudstack 4.0

2. Checkout and build latest code

  • Checkout and build the code on both machines 1 and 2
    • git clone git@github.com:gilt/incubator-cloudstack.git
    • cd incubator-cloudstack
    • mvn clean install

3. Setup management server

  • Load the data model
    • cd incubator-cloustack
    • mvn -P developer -pl developer -Ddeploydb
  • Run the management server
    • mvn -pl :cloud-client-ui jetty:run
  • Load LXC data model
    • load cloudstack/setup/db/lxc.sql
  • Restart management server

4. Configuring the agents

  • On machine 2, edit /etc/cloud/agent/agent.properties and add
    • hypervisor.type=lxc
  • Modify /etc/init.d/cloud-agent
    • Replace the "export CLASSPATH" line with
    • Code Block
      
PCP=""
for jarfile in <incubator-cloudstack-dir>/client/target/cloud-client-ui-4.1.0-SNAPSHOT/WEB-INF/lib/cloud-* /usr/share/java/jna.jar; do
    if [ ! -e "$jarfile" ] ; then continue ; fi
    PCP=$jarfile:$PCP
done
export CLASSPATH="$SCP:$DCP:$PCP:$JCP:/etc/cloud/agent:/usr/lib64/cloud/agent"
  • Restart cloud-agent on both machines
    • service cloud-agent restart

5. Setup KVM, modify SSVM

In this step we bring up the system with a KVM hypervisor. After the Secondary Storage VM starts up, we will swap out the cloud jars with the ones we've built.

  • From the Cloudstack UI: add a zone, pod, cluster, host, primary, and secondary for KVM
  • After the Secondary Storage VM starts up:
    • Code Block
      
ssh -i /root/.ssh/id_rsa.cloud -p 3922 root@169.254.x.x (SSVM local link ip)
cp -r /usr/local/cloud/systemvm /usr/local/cloud/systemvm.orig
rm /usr/local/cloud/systemvm/cloud-*.jar
scp root@<machine1>:<incubator-cloudstack-dir>/client/target/cloud-client-ui-4.1.0-SNAPSHOT/WEB-INF/lib/cloud-*.jar /usr/local/cloud/systemvm
service cloud stop
service cloud start

6. Setup LXC

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discussed the possibility of creating System VMs for LXC. There was concern with the complexity and potential issues involving iptables for the router inside an LXC container. As an intermediate solution we are going to use KVM System VMs inside the LXC Cluster.

Direct Networking

Libvirt supports direct attachment of the guest VM's network to a physical interface. To enable this mode, add the following to agent.properties:

Code Block

libvirt.vif.driver=com.cloud.hypervisor.kvm.resource.DirectVifDriver
network.direct.source.mode=private (other values: bridge|vepa)
network.direct.device=eth0

NOTE: The network device that is specified should not be a slave to any bridges.

Environment setup and testing

Obtaining latest code

The LXC code has been merged to the master branch for Cloudstack:

Code Block

git clone https://git-wip-us.apache.org/repos/asf/cloudstack.git

Follow directions in /docs/en-US/build-rpm.xml to build RPMs for Cloudstack.

Installing Cloudstack

I will not cover how to install Cloudstack, please use the latest online documents. There are a few things to note when using the LXC code:

1. Use the latest system VM images from Jenkins

Import the latest system VM image:

Code Block

/web/cloudstack/scripts/storage/secondary/cloud-install-sys-tmplt -m /mnt/secondary -u http://jenkins.cloudstack.org/view/master/job/build-systemvm-master/lastSuccessfulBuild/artifact/tools/appliance/dist/systemvmtemplate-2013-04-14-master-kvm.qcow2.bz2 -h kvm -F

2. LXC container

Cloudstack will not come bundled with an LXC container image, so you will need to prepare one yourself or download one.

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