Realizing Linux Containers (LXC)
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Transcript of Realizing Linux Containers (LXC)
Realizing Linux Containers (LXC)Building Blocks, Underpinnings & Motivations
Boden Russell – IBM Global Technology Services([email protected])
04/07/2023 2
Definitions Linux Containers (LXC for LinuX Containers) are lightweight virtual machines (VMs)
which are realized using features provided by a modern Linux kernel – VMs without the hypervisor
Containerization of:– (Linux) Operating Systems– Single or multiple applications
LXC as a technology not to be confused with LXC (tools) which are a user space toolset for creating & managing Linux Containers
From wikipedia:LXC (LinuX Containers) is an operating system–level virtualization method for running multiple isolated Linux systems (containers) on a single control host… LXC provides operating system-level virtualization not via a virtual machine, but rather provides a virtual environment that has its own process and network space.
04/07/2023 3
Why LXC
Provision in seconds / milliseconds Near bare metal runtime performance VM-like agility – it’s still “virtualization” Flexibility
– Containerize a “system”– Containerize “application(s)”
Lightweight– Just enough Operating System (JeOS)– Minimal per container penalty
Open source – free – lower TCO Supported with OOTB modern Linux kernel Growing in popularity
“Linux Containers as poised as the next VM in our modern Cloud era…”
Manual VM LXC
Provision Time
Days
Minutes
Seconds / ms
linpack performance @ 45000
0
50
100
150
200
250
vcpus
GF
lop
s
Google trends - LXC Google trends - docker
04/07/2023 4
Hypervisors vs. Linux Containers
Hardware
Operating System
Hypervisor
Virtual Machine
Operating System
Bins / libs
App App
Virtual Machine
Operating System
Bins / libs
App App
Hardware
Hypervisor
Virtual Machine
Operating System
Bins / libs
App App
Virtual Machine
Operating System
Bins / libs
App App
Hardware
Operating System
Container
Bins / libs
App App
Container
Bins / libs
App App
Type 1 Hypervisor Type 2 Hypervisor Linux Containers
Containers share the OS kernel of the host and thus are lightweight.However, each container must have the same OS kernel.
Containers are isolated, but share OS and, where appropriate, libs / bins.
04/07/2023 5
LXC Technology Stack LXCs are built on modern kernel features
– cgroups; limits, prioritization, accounting & control– namespaces; process based resource isolation– chroot; apparent root FS directory– Linux Security Modules (LSM); Mandatory Access Control (MAC)
User space interfaces for kernel functions LXC tools
– Tools to isolate process(es) virtualizing kernel resources LXC commoditization
– Dead easy LXC– LXC virtualization
Orchestration & management– Scheduling across multiple hosts– Monitoring– Uptime
04/07/2023 6
Linux cgroups History
– Work started in 2006 by google engineers– Merged into upstream 2.6.24 kernel due to wider spread LXC usage– A number of features still a WIP
Functionality– Access; which devices can be used per cgroup– Resource limiting; memory, CPU, device accessibility, block I/O, etc.– Prioritization; who gets more of the CPU, memory, etc.– Accounting; resource usage per cgroup– Control; freezing & check pointing– Injection; packet tagging
Usage– cgroup functionality exposed as “resource controllers” (aka “subsystems”)– Subsystems mounted on FS– Top-level subsystem mount is the root cgroup; all procs on host– Directories under top-level mounts created per cgroup– Procs put in tasks file for group assignment– Interface via read / write pseudo files in group
04/07/2023 7
Linux cgroup Subsystems cgroups provided via kernel modules
– Not always loaded / provided by default– Locate and load with modprobe
Some features tied to kernel version See: https://www.kernel.org/doc/Documentation/cgroups/
Subsystem Tunable Parametersblkio - Weighted proportional block I/O access. Group wide or per device.
- Per device hard limits on block I/O read/write specified as bytes per second or IOPS per second.
cpu - Time period (microseconds per second) a group should have CPU access.- Group wide upper limit on CPU time per second.- Weighted proportional value of relative CPU time for a group.
cpuset - CPUs (cores) the group can access.- Memory nodes the group can access and migrate ability.- Memory hardwall, pressure, spread, etc.
devices - Define which devices and access type a group can use.
freezer - Suspend/resume group tasks.
memory - Max memory limits for the group (in bytes).- Memory swappiness, OOM control, hierarchy, etc..
hugetlb - Limit HugeTLB size usage.- Per cgroup HugeTLB metrics.
net_cls - Tag network packets with a class ID.- Use tc to prioritize tagged packets.
net_prio - Weighted proportional priority on egress traffic (per interface).
04/07/2023 8
Linux cgroups FS Layout
04/07/2023 9
Linux cgroups Pseudo FS Interface
/sys/fs/cgroup/my-lxc
|-- blkio| |-- blkio.io_merged| |-- blkio.io_queued| |-- blkio.io_service_bytes| |-- blkio.io_serviced| |-- blkio.io_service_time| |-- blkio.io_wait_time| |-- blkio.reset_stats| |-- blkio.sectors| |-- blkio.throttle.io_service_bytes| |-- blkio.throttle.io_serviced| |-- blkio.throttle.read_bps_device| |-- blkio.throttle.read_iops_device| |-- blkio.throttle.write_bps_device| |-- blkio.throttle.write_iops_device| |-- blkio.time| |-- blkio.weight| |-- blkio.weight_device| |-- cgroup.clone_children| |-- cgroup.event_control| |-- cgroup.procs| |-- notify_on_release| |-- release_agent| `-- tasks|-- cpu| |-- ...|-- ...`-- perf_event
echo "8:16 1048576“ > blkio.throttle.read_bps_
device
cat blkio.weight_devicedev weight8:1 2008:16 500
App
App
App
Linux pseudo FS is the interface to cgroups– Read / write to pseudo file(s) in your cgroup directory
Some libs exist to interface with pseudo FS programmatically
04/07/2023 10
Linux cgroups: CPU Usage Use CPU shares (and other controls) to prioritize jobs / containers Carry out complex scheduling schemes Segment host resources Adhere to SLAs
04/07/2023 11
Linux cgroups: CPU Pinning Pin containers / jobs to CPU cores Carry out complex scheduling schemes Reduce core switching costs Adhere to SLAs
04/07/2023 12
Linux cgroups: Device Access Limit device visibility; isolation Implement device access controls
– Secure sharing Segment device access Device whitelist / blacklist
04/07/2023 13
LXC Realization: Linux cgroups cgroup created per container (in each cgroup subsystem) Prioritization, access, limits per container a la cgroup controls Per container metrics (bean counters)
04/07/2023 14
Linux namespaces History
– Initial kernel patches in 2.4.19– Recent 3.8 patches for user namespace support – A number of features still a WIP
Functionality– Provide process level isolation of global resources
• MNT (mount points, file systems, etc.)• PID (process)• NET (NICs, routing, etc.)• IPC (System V IPC resources)• UTS (host & domain name)• USER (UID + GID)
– Process(es) in namespace have illusion they are the only processes on the system– Generally constructs exist to permit “connectivity” with parent namespace
Usage– Construct namespace(s) of desired type– Create process(es) in namespace (typically done when creating namespace)– If necessary, initialize “connectivity” to parent namespace– Process(es) in name space internally function as if they are only proc(s) on system
04/07/2023 15
Linux namespaces: Conceptual Overview
04/07/2023 16
Linux namespaces: MNT namespace Isolates the mount table – per namespace mounts mount / unmount operations isolated to namespace Mount propagation
– Shared; mount objects propagate events to one another– Slave; one mount propagates events to another, but not
vice versa– Private; no event propagation (default)
Unbindable mount forbids bind mounting itself Various tools / APIs support the mount namespace such
as the mount command– Options to make shared, private, slave, etc.– Mount with namespace support
Typically used with chroot or pivot_root for effective root FS isolation
“global” (i.e. root) namespace
“green” namespace
“red” namespace
MNT NS//proc/mnt/fsrd/mnt/fsrw/mnt/cdrom/run2
MNT NS//proc/mnt/greenfs/mnt/fsrw/mnt/cdrom
MNT NS//proc/mnt/cdrom/redns
04/07/2023 17
Linux namespaces: UTS namespace Per namespace
– Hostname– NIS domain name
Reported by commands such as hostname Processes in namespace can change UTS values – only
reflected in the child namespace Allows containers to have their own FQDN
“global” (i.e. root) namespace
“green” namespace
“red” namespace
UTS NS
globalhostrootns.com
UTS NS
greenhostgreenns.org
UTS NS
redhostredns.com
04/07/2023 18
Linux namespaces: PID namespace Per namespace PID mapping
– PID 1 in namespace not the same as PID 1 in parent namespace– No PID conflicts between namespaces– Effectively 2 PIDs; the PID in the namespace and the PID outside
the namespace Permits migrating namespace processes between hosts
while keeping same PID Only processes in the namespace are visible within the
namespace (visibility limited)
“global” (i.e. root) namespace
“green” namespace
“red” namespace
PID NS
PID COMMAND1 /sbin/init2 [kthreadd]3 [ksoftirqd]4 [cpuset]5 /sbin/udevd
PID NS
PID COMMAND1 /bin/bash2 /bin/vim
PID NS
PID COMMAND1 /bin/bash2 python3 node
04/07/2023 19
Linux namespaces: IPC namespace System V IPC object & POSIX message queue isolation
between namespaces– Semaphores– Shared memory– Message queues
Parent namespace connectivity– Signals– Memory polling– Sockets (if no NET namespace)– Files / file descriptors (if no mount namespace)– Events over pipe pair
“global” (i.e. root) namespace
“green” namespace
“red” namespace
IPC NSSHMID OWNER32452 root43321 boden
SEMID OWNER0 root1 boden
IPC NS
SHMID OWNER
SEMID OWNER0 root
IPC NS
SHMID OWNER
SEMID OWNER
MSQID OWNER
04/07/2023 20
Linux namespaces: NET namespace Per namespace network objects
– Network devices (eths)– Bridges– Routing tables– IP address(es)– ports– Etc
Various commands support network namespace such as ip Connectivity to other namespaces
– veths – create veth pair, move one inside the namespace and configure
– Acts as a pipe between the 2 namespaces LXCs can have their own IPs, routes, bridges, etc.
“global” (i.e. root) namespace
“green” namespace
“red” namespace
NET NSlo: UNKNOWN…eth0: UP…eth1: UP…br0: UP…
app1 IP:5000app2 IP:6000app3 IP:7000
NET NS
lo: UNKNOWN…eth0: UP…
app1 IP:1000app2 IP:7000
NET NS
lo: UNKNOWN…eth0: DOWN…eth1: UP
app1 IP:7000app2 IP:9000
04/07/2023 21
Linux namespaces: USER namespace A long work in progress – still development for XFS and other
FS support– Significant security impacts– A handful of security holes already found + fixed
Two major features provided:– Map UID / GID from outside the container to UID / GID inside the
container– Permit non-root users to launch LXCs– Distro’s rolling out phased support, with UID / GID mapping
typically 1st
First process in USER namespace has full CAPs; perform initializations before other processes are created– No CAPs in parent namespace
UID / GID map can be pre-configured via FS Eventually USER namespace will mitigate many perceived LXC
security concerns
“global” (i.e. root) namespace
“green” namespace
“red” namespace
USER NS
root 0:0ntp 104:109Mysql 105:110boden 106:111
USER NS
root 0:0app 106:111
USER NS
root 0:0app 104:109
04/07/2023 22
LXC Realization: Linux namespaces A set of namespaces created for the container Container process(es) “executed” in the namespace set Process(es) in the container have isolated view of resources Connectivity to parent where needed (via lxc tooling)
04/07/2023 23
Linux namespaces & cgroups: Availability
Note: user namespace support in upstream kernel 3.8+, but distributions rolling out phased support:- Map LXC UID/GID between
container and host- Non-root LXC creation
04/07/2023 24
Linux chroots Changes apparent root directory for process and children
– Search paths– Relative directories– Etc
Using chroot can be escaped given proper capabilities, thus pivot_root is often used instead– chroot; points the processes file system root to new directory – pivot_root; detaches the new root and attaches it to process root directory
Often used when building system images– Chroot to temp directory– Download and install packages in chroot– Compress chroot as a system root FS
LXC realization– Bind mount container root FS (image)– Launch (unshare or clone) LXC init process in a new MNT namespace– pivot_root to the bind mount (root FS)
04/07/2023 25
Linux chroot vs pivot_root Using pivot_root with MNT namespace addresses escaping chroot concerns The pivot_root target directory becomes the “new root FS”
04/07/2023 26
LXC Realization: ImagesLXC images provide a flexible means to deliver only what you need – lightweight and minimal footprint
Basic constraints– Same architecture– Same endian– Linux’ish Operating System; you can run different Linux distros on same host
Image types– System; images intended to virtualize Operating System(s) – standard distro root FS less the kernel– Application; images intended to virtualize application(s) – only package apps + dependencies (aka
JeOS – Just enough Operating System) Bind mount host libs / bins into LXC to share host resources Container image init process
– Container init command provided on invocation – can be an application or a full fledged init process
– Init script customized for image – skinny SysVinit, upstart, etc.– Reduces overhead of lxc start-up and runtime foot print
Various tools to build images– SuSE Kiwi– Debootstrap– Etc.
LXC tooling options often include numerous image templates
04/07/2023 27
Linux Security Modules & MAC Linux Security Modules (LSM) – kernel modules which provide a framework for
Mandatory Access Control (MAC) security implementations MAC vs DAC
– In MAC, admin (user or process) assigns access controls to subject / initiator• Most MAC implementations provide the notion of profiles• Profiles define access restrictions and are said to “confine” a subject
– In DAC, resource owner (user) assigns access controls to individual resources Existing LSM implementations include: AppArmor, SELinux, GRSEC, etc.
04/07/2023 28
Linux Capabilities & Other Security Measures Linux capabilities
– Per process privileges which define operational (sys call) access– Typically checked based on process EUID and EGID– Root processes (i.e. EUID = GUID = 0) bypass capability checks
Capabilities can be assigned to LXC processes to restrict Other LXC security mitigations
– Reduce shared FS access using RO bind mounts– Keep Linux kernel up to date– User namespaces in 3.8+ kernel
• Allow to launch containers as non-root user• Map UID / GID inside / outside of container
04/07/2023 29
LXC Realization
04/07/2023 30
LXC Tooling LXC is not a kernel feature – it’s a technology enabled via kernel features
– User space tooling required to manage LXCs effectively Numerous toolsets exist
– Then: add-on patches to upstream kernel due to slow kernel acceptance– Now: upstream LXC feature support is growing – less need for patches
More popular GNU Linux toolsets include libvirt-lxc and lxc (tools)– OpenVZ is likely the most mature toolset, but it requires kernel patches– Note: I would consider docker a commoditization of LXC
Non-GNU Linux based LXC– Solaris zones– BSD jails– Illumos / SmartOS (solaris derivatives)– Etc.
04/07/2023 31
LXC Industry Tooling
04/07/2023 32
Libvirt-lxc Perhaps the simplest to learn through a familiar virsh interface Libvirt provides LXC support by connecting to lxc:/// Many virsh commands work
• virsh -c lxc:/// define sample.xml • virsh –c lxc:/// start sample• virsh –c lxc:/// console sample• virsh –c lxc:/// shutdown sample• virsh –c lxc:/// undefine sample
No snapshotting, templates… OpenStack support since Grizzly
No VNC No Cinder support in Grizzly Config drive not supported
Alternative means of accessing metadata Attached disk rather than http calls
<domain type='lxc'> <name>sample</name> <memory>32768</memory> <os> <type>exe</type> <init>/init</init> </os> <vcpu>1</vcpu> <clock offset='utc'/> <on_poweroff>destroy</on_poweroff> <on_reboot>restart</on_reboot> <on_crash>destroy</on_crash> <devices> <emulator>/usr/libexec/libvirt_lxc</emulator> <filesystem type='mount'> <source dir='/opt/vm-1-root'/> <target dir='/'/> </filesystem> <interface type='network'> <source network='default'/> </interface> <console type='pty' /> </devices> </domain>
04/07/2023 33
LXC (tools) A little more functionality Supported by the major distributions LXC 1.0 recently released
– Cloning supported: lxc-clone– Templates… btrfs– lxc-create -t ubuntu -n CN creates a new ubuntu container
• “template” is downloaded from Ubuntu• Some support for Fedora <= 14• Debian is supported
– lxc-start -d -n CN starts the container– lxc-destroy -n CN destroys the container– /etc/lxc/lxc.conf has default settings– /var/lib/lxc/CN is the default place for each container
04/07/2023 34
LXC Commoditization: docker Young project with great vibrancy in the industry Currently based on unmodified LXC – but the goal is to make it dirt easy As of March 10th, 2014 at v0.9. Monthly releases, 1.0 should be ready for production use What docker adds to LXC
– Portable deployment across machines• In Cloud terms, think of LXC as the hypervisor and docker as the Open Virtualization Appliance (OVA) and the provision engine• Docker images can run unchanged on any platform supporting docker
– Application-centric• User facing function geared towards application deployment, not VM analogs [!]
– Automatic build• Create containers from build files• Builders can use chef, maven, puppet, etc.
– Versioning support• Think of git for docker containers• Only delta of base container is tracked
– Component re-use• Any container can be used as a base, specialized and saved
– Sharing• Support for public/private repositories of containers
– Tools• CLI / REST API for interacting with docker• Vendors adding tools daily
Docker containers are self contained – no more “dependency hell”
04/07/2023 35
Docker vs. LXC vs. Hypervisor
04/07/2023 36
Docker: LXC Virtualization? Docker decouples the LXC provider from the operations
– LXC provider agnostic Docker “images” run anywhere docker is supported
– Portability
04/07/2023 37
LXC Orchestration & Management Docker & libvirt-lxc in OpenStack
– Manage containers heterogeneously with traditional VMs… but not w/the level of support & features we might like
CoreOS– Zero-touch admin Linux distro with docker images as the unit of operation– Centralized key/value store to coordinate distributed environment
Various other 3rd party apps– Maestro for docker– Shipyard for docker– Fleet for CoreOS– Etc.
LXC migration– Container migration via criu
But…– Still no great way to tie all virtual resources together with LXC – e.g. storage + networking
• IMO; an area which needs focus for LXC to become more generally applicable
04/07/2023 38
Docker in OpenStack Introduced in Havana
– A nova driver to integrate with docker REST API– A Glance translator to integrate containers with Glance
• A docker container which implements a docker registry API
The claim is that docker will become a “group A” hypervisor– In it’s current form it’s effectively a “tech preview”
04/07/2023 39
LXC Evaluation Goal: validate the promise with an eye towards practical applicability Dimensions evaluated:
– Runtime performance benefits– Density / footprint– Workload isolation– Ease of use and tooling– Cloud Integration– Security– Ease of use / feature set
NOTE: tests performed in a passive manner – deeper analysis warrented.
04/07/2023 40
Runtime Performance Benefits - CPU Tested using libvirt lxc on Ubuntu 13.10 using linpack 11.1 Cpuset was used to limit the number of CPUs that the containers could use The performance overhead falls within the error of measurement of this test Actual bare metal performance is actually lower than some container results
linpack performance @ 45000
0
50
100
150
200
250
1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 BM
vcpus
GF
lop
s
220.77Bare metal220.5
@32 vcpu
220.9@ 31 vcpu
04/07/2023 41
Runtime Performance Benefits – I/O I/O Tests using libvirt lxc show a < 1 % degradation Tested with a pass-through mount
Sync read I/O test
Rw=WriteSize=1024mBs=128mbdirect=1sync=1
Sync write I/O test
Rw=WriteSize=1024mBs=128mbdirect=1sync=1
I/O throughput
1711.2 1724.9 1626.4 1633.4
0
500
1000
1500
2000
lxc write bare metalwrite
lxc read bare metalread
test
MB
/s
Series1
04/07/2023 42
Runtime Performance Benefits – Block I/O Tested with [standard] AUFS
04/07/2023 43
Density & Footprint – libvirt-lxc
Starting 500 containersMon Nov 11 13:38:49 CST 2013 ... all threads done in 157(sequential I/O bound)
Stopping 500 containersMon Nov 11 13:42:20 CST 2013 ... all threads done in 162Active memory delta: 417.2 KB
Starting 1000 containersMon Nov 11 13:59:19 CST 2013 ... all threads done in 335
Stopping 1000 containersMon Nov 11 14:14:26 CST 2013 ... all threads done in 339Active memory delta: 838.4KB
Using libvirt lxc on RHEL 6.4, we found that empty container overhead was just 840 bytes. A container could be started in about 330ms, which was an I/O bound processThis represents the lower limit of lxc footprintContainers ran /bin/sh
04/07/2023 44
Density & Footprint – Docker In this test, we created 150 Docker containers with CentOS, started
apache & then removed them Average footprint was ~10MB per container Average start time was 240ms
Serially booting 150 containers which run apache – Takes on average 36 seconds– Consumes about 2 % of the CPU– Negligible HDD space– Spawns around 225 processes for create– Around 1.5 GB of memory ~ 10 MB per container– Expect faster results once docker addresses performance topics in the
next few months
Serially destroying 150 containers running apache– On average takes 9 seconds– We would expect destroy to be faster – likely a docker bug and will triage
with the docker community
Container Creation
Container Deletion
I/O profile
CPU profile
04/07/2023 45
Workload Isolation: Examples Using the blkio cgroup (lxc.cgroup.blkio.throttle.read_bps_device) to cap the I/O of a container Both the total bps and iops_device on read / write could be capped Better async BIO support in kernel 3.10+
We used fio with oflag=sync, direct to test the ability to cap the reads:
– With limit set to 6 MB / secondREAD: io=131072KB, aggrb=6147KB/s, minb=6295KB/s, maxb=6295KB/s,
mint=21320msec, maxt=21320msec
– With limit set to 60 MB / secondREAD: io=131072KB, aggrb=61134KB/s, minb=62601KB/s, maxb=62601KB/s,
mint=2144msec, maxt=2144msec
– No read limitREAD: io=131072KB, aggrb=84726KB/s, minb=86760KB/s, maxb=86760KB/s,
mint=1547msec, maxt=1547msec
04/07/2023 46
OpenStack VM OperationsNOTE: orchestration / management overheads cap LXC performance
04/07/2023 47
Who’s Using LXC Google app engine & infra is said to be using some form of LXC RedHat OpenShift dotCloud (now docker inc) CloudFoundry (early versions) Rackspace Cloud Databases
– Outperforms AWS (Xen) according to perf results
Parallels Virtuozzo (commercial product) Etc..
04/07/2023 48
LXC Gaps
There are gaps…
Lack of industry tooling / support Live migration still a WIP Full orchestration across resources (compute / storage / networking) Fears of security Not a well known technology… yet Integration with existing virtualization and Cloud tooling Not much / any industry standards Missing skillset Slower upstream support due to kernel dev process Etc.
04/07/2023 49
LXC: Use Cases For Traditional VMs
There are still use cases where traditional VMs are warranted.
Virtualization of non Linux based OSs– Windows– AIX– Etc.
LXC not supported on host VM requires unique kernel setup which is not applicable to other VMs on the host
(i.e. per VM kernel config) Etc.
04/07/2023 50
LXC Recommendations Public & private Clouds
– Increase VM density 2-3x– Accommodate Big Data & HPC type applications– Move the support of Linux distros to containers
PaaS & managed services– Realize “as a Service” and managed services using LXC
Operations management– Ease management + increase agility of bare metal components
DevOps Development & test
– Sandboxes– Dev / test envs– Etc.
If you are just starting with LXC and don’t have in-depth skillset– Start with LXC for private solutions (trusted code)
04/07/2023 51
LXC Resources https://www.kernel.org/doc/Documentation/cgroups/ http://www.blaess.fr/christophe/2012/01/07/linux-3-2-cfs-cpu-bandwidth-english-version/ http://atmail.com/kb/2009/throttling-bandwidth/ https://
access.redhat.com/site/documentation/en-US/Red_Hat_Enterprise_Linux/6/html/Resource_Management_Guide/ch-Subsystems_and_Tunable_Parameters.html
http://www.janoszen.com/2013/02/06/limiting-linux-processes-cgroups-explained/ http://www.mattfischer.com/blog/?p=399 http://oakbytes.wordpress.com/2012/09/02/cgroup-cpu-allocation-cpu-shares-examples/ http://fritshoogland.wordpress.com/2012/12/15/throttling-io-with-linux/ https://lwn.net/Articles/531114/ https://www.kernel.org/doc/Documentation/filesystems/sharedsubtree.txt http://www.ibm.com/developerworks/library/l-mount-namespaces/ http://blog.endpoint.com/2012/01/linux-unshare-m-for-per-process-private.html http://timothysc.github.io/blog/2013/02/22/perprocess/ http://www.evolware.org/?p=293 http://s3hh.wordpress.com/2012/05/10/user-namespaces-available-to-play/ http://libvirt.org/drvlxc.html https://help.ubuntu.com/lts/serverguide/lxc.html https://linuxcontainers.org/ https://wiki.ubuntu.com/AppArmor http://linux.die.net/man/7/capabilities http://docs.openstack.org/trunk/config-reference/content/lxc.html https://wiki.openstack.org/wiki/Docker https://www.docker.io/ http://marceloneves.org/papers/pdp2013-containers.pdf http://openvz.org/Main_Page http://criu.org/Main_Page