Dobrica Pavlinušić's random unstructured stuff
LXC: Revision 33

This are notes for my LXC workshop, in state of flux

Contents


Cgroups

Systemd

launchd alterntive, somilar to inetd, but for unix sockets (mostly)

LXC

Virtual Servers and Checkpoint/Restart in Mainstream Linux http://lxc.sourceforge.net/doc/sigops/appcr.pdf

LXC inside KVM for testing

setup KVM LXC test machine

Step 1: Create a root filesystem for the KVM system.

Step 2: Build a kernel for KVM, with container support.

Step 3: Boot the result under QEMU or KVM

Step 4: ssh into the KVM instance.

ssh root@127.0.0.1 -p 9876

Step 5: Set up a simple busybox-based container under the KVM system.

wget http://busybox.net/downloads/binaries/latest/busybox-i686 -O busybox
chmod +x busybox
echo -e "lxc.utsname = container\nlxc.network.type = empty" > container.conf
PATH=$(pwd):$PATH lxc-create -f container.conf -t busybox -n container

Step 6: Launch the container

lxc-start -n container

# console is broken, so start another

lxc-console -n container

Step 7: Stop the container, and the KVM system.

lxc-stop -n container

# remove container
lxc-destroy -n container

Setup networking

Step 1: Add a TAP interface to the Laptop.

# FIXME change username
tunctl -u dpavlin -t kvm0
ifconfig kvm0 192.168.254.1 netmask 255.255.255.0
echo 1 > /proc/sys/net/ipv4/ip_forward

# iptables -t nat -A POSTROUTING -o eth0 -j MASQUERADE

Step 2: Launch KVM with two ethernet interfaces.

kvm -m 1024 -kernel ../01-setup/linux-2.6.*/arch/x86/boot/bzImage -no-reboot \
    -hda ../01-setup/squeeze.ext3 -append "root=/dev/hda rw panic=1" \
    -net nic,model=e1000 -net user -redir tcp:9876::22 \
    -net nic,model=e1000 -net tap,ifname=kvm0,script=no

Step 3: Set up a new container in the KVM system.

root@kvm:~# cat > busybox.conf << EOF
lxc.utsname = busybox
lxc.network.type = phys
lxc.network.flags = up
lxc.network.link = eth1
#lxc.network.name = eth0
EOF

PATH=$(pwd):$PATH lxc-create -f busybox.conf -t busybox -n busybox
lxc-start -n busybox


root@kvm:~# lxc-console -n busybox

ifconfig eth1 192.168.254.2 netmask 255.255.255.0
route add default gw 192.168.254.1

Step 4: Fun with routing.

On host, bring up loopback alias in KVM network:

dpavlin@x200:~$ sudo ifconfig lo:1 10.0.2.200 netmask 255.255.255.0

busybox container can reach it, while KVM can't !

network hints

prepare host machine

macvlan

  • aliased IP at eth devel
  • new device with own mac with offloading
  • can't communicate with other containers or host (< 2.6.33)

lxc.network.type=macvlan
lxc.network.link=eth0
lxc.network.flags=up

ip link add link <phys> name <vif> address <mac address> type macvlan mode (bridge|vepa|private)

ip link add link bond200 name bond200:0 address 00:aa:bb:cc:dd:ee type macvlan mode bridge

ip -d show link bond200:0

lxc.network.type = macvlan
lxc.network.macvlan.mode = bridge
lxc.network.flags = up
lxc.network.link = bond200
lxc.network.name = eth7
lxc.network.mtu = 1500
lxc.network.ipv4 = 192.168.90.11/24
lxc.network.hwaddr = 4a:49:43:49:79:0B

veth

sudo apt-get install bridge-utils dnsmasq


# setup hints

sysctl -w net.ipv4.ip_forward=1

ptables -t nat -A POSTROUTING -o wlan0 -j SNAT --to-source=WLAN0_IP

# or for nat
iptables -t nat -A POSTROUTING -o wlan0 -j MASQUERADE

lxc.network.type=veth
lxc.network.link=br0
lxc.network.flags=up

  1. name inside container

lxc.network.name = eth0.12
lxc.network.mtu = 1500
lxc.network.ipv4 = 10.60.0.12/23
lxc.network.hwaddr = AC:DE:48:00:00:0C

  1. name host interface for bridge

lxc.network.veth.pair = veth12

host-only bridge

$ cat /etc/network/interfaces

auto br0
iface br0 inet static
        bridge_ports dummy0
        bridge_maxwait 0
        address 172.16.16.1
        netmask 255.255.255.0

pseudo-random mac?

http://en.wikipedia.org/wiki/Mac_address

    x2:xx:xx:xx:xx:xx
    x6:xx:xx:xx:xx:xx
    xA:xx:xx:xx:xx:xx
    xE:xx:xx:xx:xx:xx

IP=192.168.0.50 # container nic IP
HA=printf "02:00:%x:%x:%x:%x" ${IP//./ } # generate a MAC from the IP

slow network?

/usr/sbin/ethtool -K br0 sg off
/usr/sbin/ethtool -K br0 tso off

phys

kernel > 2.6.35

lxc.network.type=phys
lxc.network.link=eth1
lxc.network.name=eth1

limit container resources

cpuset.cpus

echo 1 > /cgroup/<name>/cpuset.cpus # 2nd CPU!

echo 1,2,3 > /cgroup/<name>/cpuset.cpus

echo 0-7 > /cgroup/<name>/cpuset.cpus

lxc-execute -n foo -s lxc.cgroup.cpuset.cpus="1,2,3" myforks

cpu.shares

lxc-execute -n foo -s lxc.cgroup.cpu.shares=1 /bin/bash

lxc-execute -n bar -s /bin/bash

while $(true); do echo -n . ; done

lxc-cgroup -n foo cpu.shares=1024

memory

lxc.cgroup.memory.limit_in_bytes = 256M
lxc.cgroup.memory.memsw.limit_in_bytes = 1G

disk

usage

standard Linux tools:

  • LVM
  • quota (it can be bypassed if the container runs with CAP_SYS_ADMIN and/or CAP_SYS_RESOURCE capabilities)

limit disk bandwith using cgroup blkio

Required kernel configuration

CONFIG_BLK_CGROUP=y
CONFIG_CFQ_GROUP_IOSCHED=y
CONFIG_BLK_DEV_THROTTLING=y

create containers for test

#!/bin/sh -xe

lxc-ls | xargs -i sh -c "lxc-stop -n {} ; lxc-destroy -n {}"

echo "lxc.network.type = empty" > blkio.conf

PATH=$(pwd):$PATH lxc-create -f blkio.conf -t busybox -n disk1
PATH=$(pwd):$PATH lxc-create -f blkio.conf -t busybox -n disk2
PATH=$(pwd):$PATH lxc-create -f blkio.conf -t busybox -n disk3

lxc-ls | xargs -i dd if=/dev/zero of=/var/lib/lxc/{}/rootfs/tmp/zero bs=1M count=100

cat > /tmp/speed.sh <<EOF
#!/bin/sh
while true ; do
        sync ; echo 3 > /proc/sys/vm/drop_caches
        dd if=/tmp/zero of=/dev/null 2>&1
done | grep MB
EOF

chmod +x /tmp/speed.sh

lxc-ls | xargs -i cp /tmp/speed.sh /var/lib/lxc/{}/rootfs/tmp/speed.sh

lxc-ls | xargs -i lxc-start -d -n {}

login into each container and run test

root@kvm:~# lxc-console -n disk1

Type <Ctrl+a q> to exit the console

disk1 login: root
~ # /tmp/speed.sh 
104857600 bytes (100.0MB) copied, 0.958453 seconds, 104.3MB/s

Test limits (be careful not to enter 1000, you might oops kernel!)

root@kvm:~# echo 100 > /mnt/cgroup/disk1/blkio.weight
root@kvm:~# echo 200 > /mnt/cgroup/disk2/blkio.weight
root@kvm:~# echo 500 > /mnt/cgroup/disk3/blkio.weight

root@kvm:~# cat /mnt/cgroup/disk?/blkio.weight
100
200
500

Limit /dev/hda to 1Mb/s read

root@kvm:~# ls -al /dev/hda
brw-rw---- 1 root disk 3, 0 May 15 00:10 /dev/hda

root@kvm:~# echo "3:0 1048576" > /mnt/cgroup/disk1/blkio.throttle.read_bps_device

network

# mkdir -p /dev/cgroup
# mount -t cgroup net_cls -o net_cls /dev/cgroup
# mkdir /dev/cgroup/A
# mkdir /dev/cgroup/B

# cd /dev/cgroup
# echo 0x1001 > A/net_cls.classid # 10:1
# echo 0x1002 > B/net_cls.classid # 10:2

# tc qdisc add dev eth0 root handle 10: htb

# tc class add dev eth0 parent 10: classid 10:1 htb rate 40mbit
# tc class add dev eth0 parent 10: classid 10:2 htb rate 30mbit

# tc filter add dev eth0 parent 10: protocol ip prio 10 handle 1: cgroup

LXC commands

lxc-create

/usr/lib/lxc/templates/

export MIRROR=http://192.168.1.20:3142/ftp.debian.org
export SUITE=lenny

cat > /tmp/lenny.conf
lxc.network.type=veth
lxc.network.link=br0
lxc.network.flags=up

  1. <ctrl+d>

t61p:~# lxc-create -n lenny -t debian -f /tmp/lenny.conf

lxc-execute

application container (shares filesystem!)

lxc-ssh

lxc-execute -n foo -s lxc.utsname=foo /bin/bash
lxc-execute -n bar -s lxc.utsname=bar /bin/bash

lxc-attach

Needs kernel patch

lxc-attach n n0 - /usr/sbin/tcpdump -i eth0

devices

http://lwn.net/Articles/273208/

lxc.cgroup.devices.allow = <type> <major>:<minor> <perm>

<type> : b (block), c (char), etc ...
<major> : major number
<minor> : minor number (wildcard is accepted)
<perms> : r (read), w (write), m (mapping)

monitoring

htop

htop - cgroups > r192

t61p:/tmp# apt-get source htop
t61p:/tmp# apt-get build-dep htop
t61p:/tmp# dpkg-source -x htop_0.9-2.dsc
t61p:/tmp# cd htop-0.9/

t61p:/tmp/htop-0.9# DEB_BUILD_OPTIONS="--enable-cgroup" fakeroot debian/rules binary

  1. sigh, no work, patch debian/rules to add --enable-cgroup

t61p:/tmp/htop-0.9# fakeroot debian/rules binary
t61p:/tmp/htop-0.9# dpkg -i ../htop_0.9-2_i386.deb

procfs

http://lxc.sourceforge.net/download/procfs/procfs.tar.gz (fuse, defunct)
http://www.tinola.com/lxc/ (somewhat newer)

debugging

lxc-start --logpriority=TRACE -o /tmp/trace.log --name my_container

(must have redirect to file!)

kernel patches

http://lxc.sourceforge.net/patches/linux/

Are we in container?

on host:

dpavlin@stage:~$ cat /proc/$$/cgroup
1:net_cls,freezer,devices,cpuacct,cpu,ns,cpuset:/

inside container:

dpavlin@narada:~$ cat /proc/$$/cgroup
1:net_cls,freezer,devices,cpuacct,cpu,ns,cpuset:/narada

32-bit guest on 64-bit kernel

(lxc >= 0.7.3)

lxc.arch=x86

Container tweaks

udev

echo udev hold | dpkg --set-selections

nfs

kernel doesn't have nfs namespaces yet, use user-space nfs servers:

chromium

pam

pam_netns allows to setup a private network namespace for every user
session (comparable with pam_namespace for filesystem namespaces). This
is especially useful on multiseat environments.

X-server

Virtual PCI network cards

don't delete files

dpkg-divert --rename /etc/init/theinitfile.conf

.pre