Containers are a lightweight alternative to fully virtualized VMs. Instead of emulating a complete Operating System (OS), containers simply use the OS of the host they run on. This implies that all containers use the same kernel, and that they can access resources from the host directly.
This is great because containers do not waste CPU power nor memory due to kernel emulation. Container run-time costs are close to zero and usually negligible. But there are also some drawbacks you need to consider:
-
You can only run Linux based OS inside containers, i.e. it is not possible to run FreeBSD or MS Windows inside.
-
For security reasons, access to host resources needs to be restricted. This is done with AppArmor, SecComp filters and other kernel features. Be prepared that some syscalls are not allowed inside containers.
Proxmox VE uses LXC as underlying container
technology. We consider LXC as low-level library, which provides
countless options. It would be too difficult to use those tools
directly. Instead, we provide a small wrapper called pct
, the
"Proxmox Container Toolkit".
The toolkit is tightly coupled with Proxmox VE. That means that it is aware of the cluster setup, and it can use the same network and storage resources as fully virtualized VMs. You can even use the Proxmox VE firewall, or manage containers using the HA framework.
Our primary goal is to offer an environment as one would get from a VM, but without the additional overhead. We call this "System Containers".
|
If you want to run micro-containers (with docker, rkt, …), it is best to run them inside a VM. |
Security Considerations
Containers use the same kernel as the host, so there is a big attack surface for malicious users. You should consider this fact if you provide containers to totally untrusted people. In general, fully virtualized VMs provide better isolation.
The good news is that LXC uses many kernel security features like AppArmor, CGroups and PID and user namespaces, which makes containers usage quite secure. We distinguish two types of containers:
Privileged containers
Security is done by dropping capabilities, using mandatory access control (AppArmor), SecComp filters and namespaces. The LXC team considers this kind of container as unsafe, and they will not consider new container escape exploits to be security issues worthy of a CVE and quick fix. So you should use this kind of containers only inside a trusted environment, or when no untrusted task is running as root in the container.
Unprivileged containers
This kind of containers use a new kernel feature called user namespaces. The root uid 0 inside the container is mapped to an unprivileged user outside the container. This means that most security issues (container escape, resource abuse, …) in those containers will affect a random unprivileged user, and so would be a generic kernel security bug rather than an LXC issue. The LXC team thinks unprivileged containers are safe by design.
Configuration
The /etc/pve/lxc/<CTID>.conf file stores container configuration, where <CTID> is the numeric ID of the given container. Like all other files stored inside /etc/pve/, they get automatically replicated to all other cluster nodes.
|
CTIDs < 100 are reserved for internal purposes, and CTIDs need to be unique cluster wide. |
ostype: debian
arch: amd64
hostname: www
memory: 512
swap: 512
net0: bridge=vmbr0,hwaddr=66:64:66:64:64:36,ip=dhcp,name=eth0,type=veth
rootfs: local:107/vm-107-disk-1.raw,size=7G
Those configuration files are simple text files, and you can edit them using a normal text editor (vi, nano, …). This is sometimes useful to do small corrections, but keep in mind that you need to restart the container to apply such changes.
For that reason, it is usually better to use the pct command to generate and modify those files, or do the whole thing using the GUI. Our toolkit is smart enough to instantaneously apply most changes to running containers. This feature is called "hot plug", and there is no need to restart the container in that case.
File Format
Container configuration files use a simple colon separated key/value format. Each line has the following format:
# this is a comment
OPTION: value
Blank lines in those files are ignored, and lines starting with a # character are treated as comments and are also ignored.
It is possible to add low-level, LXC style configuration directly, for example:
lxc.init_cmd: /sbin/my_own_init
or
lxc.init_cmd = /sbin/my_own_init
Those settings are directly passed to the LXC low-level tools.
Snapshots
When you create a snapshot, pct stores the configuration at snapshot time into a separate snapshot section within the same configuration file. For example, after creating a snapshot called testsnapshot, your configuration file will look like this:
memory: 512
swap: 512
parent: testsnaphot
...
[testsnaphot]
memory: 512
swap: 512
snaptime: 1457170803
...
There are a few snapshot related properties like parent and snaptime. The parent property is used to store the parent/child relationship between snapshots. snaptime is the snapshot creation time stamp (unix epoch).
Guest Operating System Configuration
We normally try to detect the operating system type inside the container, and then modify some files inside the container to make them work as expected. Here is a short list of things we do at container startup:
- set /etc/hostname
-
to set the container name
- modify /etc/hosts
-
to allow lookup of the local hostname
- network setup
-
pass the complete network setup to the container
- configure DNS
-
pass information about DNS servers
- adapt the init system
-
for example, fix the number of spawned getty processes
- set the root password
-
when creating a new container
- rewrite ssh_host_keys
-
so that each container has unique keys
- randomize crontab
-
so that cron does not start at the same time on all containers
Changes made by Proxmox VE are enclosed by comment markers:
# --- BEGIN PVE ---
<data>
# --- END PVE ---
Those markers will be inserted at a reasonable location in the file. If such a section already exists, it will be updated in place and will not be moved.
Modification of a file can be prevented by adding a .pve-ignore.
file for it. For instance, if the file /etc/.pve-ignore.hosts
exists then the /etc/hosts
file will not be touched. This can be a
simple empty file creatd via:
# touch /etc/.pve-ignore.hosts
Most modifications are OS dependent, so they differ between different distributions and versions. You can completely disable modifications by manually setting the ostype to unmanaged.
OS type detection is done by testing for certain files inside the container:
- Ubuntu
-
inspect /etc/lsb-release (DISTRIB_ID=Ubuntu)
- Debian
-
test /etc/debian_version
- Fedora
-
test /etc/fedora-release
- RedHat or CentOS
-
test /etc/redhat-release
- ArchLinux
-
test /etc/arch-release
- Alpine
-
test /etc/alpine-release
- Gentoo
-
test /etc/gentoo-release
|
Container start fails if the configured ostype differs from the auto detected type. |
Options
-
arch
:(amd64 | i386)
(default=amd64
) -
OS architecture type.
-
cmode
:(console | shell | tty)
(default=tty
) -
Console mode. By default, the console command tries to open a connection to one of the available tty devices. By setting cmode to console it tries to attach to /dev/console instead. If you set cmode to shell, it simply invokes a shell inside the container (no login).
-
console
:boolean
(default=1
) -
Attach a console device (/dev/console) to the container.
-
cpulimit
:number (0 - 128)
(default=0
) -
Limit of CPU usage.
If the computer has 2 CPUs, it has a total of 2 CPU time. Value 0 indicates no CPU limit. -
cpuunits
:integer (0 - 500000)
(default=1024
) -
CPU weight for a VM. Argument is used in the kernel fair scheduler. The larger the number is, the more CPU time this VM gets. Number is relative to the weights of all the other running VMs.
You can disable fair-scheduler configuration by setting this to 0. -
description
:string
-
Container description. Only used on the configuration web interface.
-
hostname
:string
-
Set a host name for the container.
-
lock
:(backup | migrate | rollback | snapshot)
-
Lock/unlock the VM.
-
memory
:integer (16 - N)
(default=512
) -
Amount of RAM for the VM in MB.
-
mp[n]
:[volume=]<volume> ,mp=<Path> [,acl=<1|0>] [,backup=<1|0>] [,quota=<1|0>] [,ro=<1|0>] [,size=<DiskSize>]
-
Use volume as container mount point.
-
acl
=boolean
-
Explicitly enable or disable ACL support.
-
backup
=boolean
-
Whether to include the mountpoint in backups.
-
mp
=<Path>
-
Path to the mountpoint as seen from inside the container.
-
quota
=boolean
-
Enable user quotas inside the container (not supported with zfs subvolumes)
-
ro
=boolean
-
Read-only mountpoint (not supported with bind mounts)
-
size
=<DiskSize>
-
Volume size (read only value).
-
volume
=<volume>
-
Volume, device or directory to mount into the container.
-
-
nameserver
:string
-
Sets DNS server IP address for a container. Create will automatically use the setting from the host if you neither set searchdomain nor nameserver.
-
net[n]
:name=<string> [,bridge=<bridge>] [,firewall=<1|0>] [,gw=<GatewayIPv4>] [,gw6=<GatewayIPv6>] [,hwaddr=<XX:XX:XX:XX:XX:XX>] [,ip=<IPv4Format/CIDR>] [,ip6=<IPv6Format/CIDR>] [,mtu=<integer>] [,rate=<mbps>] [,tag=<integer>] [,trunks=<vlanid[;vlanid...]>] [,type=<veth>]
-
Specifies network interfaces for the container.
-
bridge
=<bridge>
-
Bridge to attach the network device to.
-
firewall
=boolean
-
Controls whether this interface’s firewall rules should be used.
-
gw
=<GatewayIPv4>
-
Default gateway for IPv4 traffic.
-
gw6
=<GatewayIPv6>
-
Default gateway for IPv6 traffic.
-
hwaddr
=<XX:XX:XX:XX:XX:XX>
-
The interface MAC address. This is dynamically allocated by default, but you can set that statically if needed, for example to always have the same link-local IPv6 address. (lxc.network.hwaddr)
-
ip
=<IPv4Format/CIDR>
-
IPv4 address in CIDR format.
-
ip6
=<IPv6Format/CIDR>
-
IPv6 address in CIDR format.
-
mtu
=integer (64 - N)
-
Maximum transfer unit of the interface. (lxc.network.mtu)
-
name
=<string>
-
Name of the network device as seen from inside the container. (lxc.network.name)
-
rate
=<mbps>
-
Apply rate limiting to the interface
-
tag
=integer (1 - 4094)
-
VLAN tag for this interface.
-
trunks
=<vlanid[;vlanid...]>
-
VLAN ids to pass through the interface
-
type
=(veth)
-
Network interface type.
-
-
onboot
:boolean
(default=0
) -
Specifies whether a VM will be started during system bootup.
-
ostype
:(alpine | archlinux | centos | debian | fedora | gentoo | opensuse | ubuntu | unmanaged)
-
OS type. This is used to setup configuration inside the container, and corresponds to lxc setup scripts in /usr/share/lxc/config/<ostype>.common.conf. Value unmanaged can be used to skip and OS specific setup.
-
protection
:boolean
(default=0
) -
Sets the protection flag of the container. This will prevent the CT or CT’s disk remove/update operation.
-
rootfs
:[volume=]<volume> [,acl=<1|0>] [,quota=<1|0>] [,ro=<1|0>] [,size=<DiskSize>]
-
Use volume as container root.
-
acl
=boolean
-
Explicitly enable or disable ACL support.
-
quota
=boolean
-
Enable user quotas inside the container (not supported with zfs subvolumes)
-
ro
=boolean
-
Read-only mountpoint (not supported with bind mounts)
-
size
=<DiskSize>
-
Volume size (read only value).
-
volume
=<volume>
-
Volume, device or directory to mount into the container.
-
-
searchdomain
:string
-
Sets DNS search domains for a container. Create will automatically use the setting from the host if you neither set searchdomain nor nameserver.
-
startup
: `[[order=]\d+] [,up=\d+] [,down=\d+] ` -
Startup and shutdown behavior. Order is a non-negative number defining the general startup order. Shutdown in done with reverse ordering. Additionally you can set the up or down delay in seconds, which specifies a delay to wait before the next VM is started or stopped.
-
swap
:integer (0 - N)
(default=512
) -
Amount of SWAP for the VM in MB.
-
template
:boolean
(default=0
) -
Enable/disable Template.
-
tty
:integer (0 - 6)
(default=2
) -
Specify the number of tty available to the container
-
unprivileged
:boolean
(default=0
) -
Makes the container run as unprivileged user. (Should not be modified manually.)
-
unused[n]
:string
-
Reference to unused volumes. This is used internally, and should not be modified manually.
Container Images
Container Images, sometimes also referred to as "templates" or "appliances", are tar archives which contain everything to run a container. You can think of it as a tidy container backup. Like most modern container toolkits, pct uses those images when you create a new container, for example:
pct create 999 local:vztmpl/debian-8.0-standard_8.0-1_amd64.tar.gz
Proxmox itself ships a set of basic templates for most common operating systems, and you can download them using the pveam (short for Proxmox VE Appliance Manager) command line utility. You can also download TurnKey Linux containers using that tool (or the graphical user interface).
Our image repositories contain a list of available images, and there is a cron job run each day to download that list. You can trigger that update manually with:
pveam update
After that you can view the list of available images using:
pveam available
You can restrict this large list by specifying the section you are interested in, for example basic system images:
# pveam available --section system
system archlinux-base_2015-24-29-1_x86_64.tar.gz
system centos-7-default_20160205_amd64.tar.xz
system debian-6.0-standard_6.0-7_amd64.tar.gz
system debian-7.0-standard_7.0-3_amd64.tar.gz
system debian-8.0-standard_8.0-1_amd64.tar.gz
system ubuntu-12.04-standard_12.04-1_amd64.tar.gz
system ubuntu-14.04-standard_14.04-1_amd64.tar.gz
system ubuntu-15.04-standard_15.04-1_amd64.tar.gz
system ubuntu-15.10-standard_15.10-1_amd64.tar.gz
Before you can use such a template, you need to download them into one of your storages. You can simply use storage local for that purpose. For clustered installations, it is preferred to use a shared storage so that all nodes can access those images.
pveam download local debian-8.0-standard_8.0-1_amd64.tar.gz
You are now ready to create containers using that image, and you can list all downloaded images on storage local with:
# pveam list local
local:vztmpl/debian-8.0-standard_8.0-1_amd64.tar.gz 190.20MB
The above command shows you the full Proxmox VE volume identifiers. They include the storage name, and most other Proxmox VE commands can use them. For examply you can delete that image later with:
pveam remove local:vztmpl/debian-8.0-standard_8.0-1_amd64.tar.gz
Container Storage
Traditional containers use a very simple storage model, only allowing a single mount point, the root file system. This was further restricted to specific file system types like ext4 and nfs. Additional mounts are often done by user provided scripts. This turend out to be complex and error prone, so we try to avoid that now.
Our new LXC based container model is more flexible regarding storage. First, you can have more than a single mount point. This allows you to choose a suitable storage for each application. For example, you can use a relatively slow (and thus cheap) storage for the container root file system. Then you can use a second mount point to mount a very fast, distributed storage for your database application.
The second big improvement is that you can use any storage type supported by the Proxmox VE storage library. That means that you can store your containers on local lvmthin or zfs, shared iSCSI storage, or even on distributed storage systems like ceph. It also enables us to use advanced storage features like snapshots and clones. vzdump can also use the snapshot feature to provide consistent container backups.
Last but not least, you can also mount local devices directly, or mount local directories using bind mounts. That way you can access local storage inside containers with zero overhead. Such bind mounts also provide an easy way to share data between different containers.
Mount Points
Beside the root directory the container can also have additional mount points. Currently there are basically three types of mount points: storage backed mount points, bind mounts and device mounts.
Storage backed mount points are managed by the Proxmox VE storage subsystem and come in three different flavors:
-
Image based: These are raw images containing a single ext4 formatted file system.
-
ZFS Subvolumes: These are technically bind mounts, but with managed storage, and thus allow resizing and snapshotting.
-
Directories: passing
size=0
triggers a special case where instead of a raw image a directory is created.
Bind mounts are considered to not be managed by the storage subsystem, so you cannot make snapshots or deal with quotas from inside the container, and with unprivileged containers you might run into permission problems caused by the user mapping, and cannot use ACLs from inside an unprivileged container.
Similarly device mounts are not managed by the storage, but for these the
quota
and acl
options will be honored.
|
Because of existing issues in the Linux kernel’s freezer subsystem the usage of FUSE mounts inside a container is strongly advised against, as containers need to be frozen for suspend or snapshot mode backups. If FUSE mounts cannot be replaced by other mounting mechanisms or storage technologies, it is possible to establish the FUSE mount on the Proxmox host and use a bind mount point to make it accessible inside the container. |
|
For security reasons, bind mounts should only be established
using source directories especially reserved for this purpose, e.g., a
directory hierarchy under /mnt/bindmounts . Never bind mount system
directories like / , /var or /etc into a container - this poses a
great security risk. The bind mount source path must not contain any symlinks. |
The root mount point is configured with the rootfs property, and you can configure up to 10 additional mount points. The corresponding options are called mp0 to mp9, and they can contain the following setting:
rootfs
: [volume=]<volume> [,acl=<1|0>] [,quota=<1|0>] [,ro=<1|0>] [,size=<DiskSize>]
mp[n]
: [volume=]<volume> ,mp=<Path> [,acl=<1|0>] [,backup=<1|0>] [,quota=<1|0>] [,ro=<1|0>] [,size=<DiskSize>]
-
acl
:boolean
-
Explicitly enable or disable ACL support.
-
backup
:boolean
-
Whether to include the mountpoint in backups.
-
mp
:<Path>
-
Path to the mountpoint as seen from inside the container.
-
quota
:boolean
-
Enable user quotas inside the container (not supported with zfs subvolumes)
-
ro
:boolean
-
Read-only mountpoint (not supported with bind mounts)
-
size
:<DiskSize>
-
Volume size (read only value).
-
volume
:<volume>
-
Volume, device or directory to mount into the container.
rootfs: thin1:base-100-disk-1,size=8G
Using quotas inside containers
Quotas allow to set limits inside a container for the amount of disk space that each user can use. This only works on ext4 image based storage types and currently does not work with unprivileged containers.
Activating the quota
option causes the following mount options to be
used for a mount point:
usrjquota=aquota.user,grpjquota=aquota.group,jqfmt=vfsv0
This allows quotas to be used like you would on any other system. You
can initialize the /aquota.user
and /aquota.group
files by running
quotacheck -cmug /
quotaon /
and edit the quotas via the edquota
command. Refer to the documentation
of the distribution running inside the container for details.
|
You need to run the above commands for every mount point by passing
the mount point’s path instead of just / . |
Using ACLs inside containers
The standard Posix Access Control Lists are also available inside containers. ACLs allow you to set more detailed file ownership than the traditional user/ group/others model.
Container Network
You can configure up to 10 network interfaces for a single container. The corresponding options are called net0 to net9, and they can contain the following setting:
net[n]
: name=<string> [,bridge=<bridge>] [,firewall=<1|0>] [,gw=<GatewayIPv4>] [,gw6=<GatewayIPv6>] [,hwaddr=<XX:XX:XX:XX:XX:XX>] [,ip=<IPv4Format/CIDR>] [,ip6=<IPv6Format/CIDR>] [,mtu=<integer>] [,rate=<mbps>] [,tag=<integer>] [,trunks=<vlanid[;vlanid...]>] [,type=<veth>]
-
bridge
:<bridge>
-
Bridge to attach the network device to.
-
firewall
:boolean
-
Controls whether this interface’s firewall rules should be used.
-
gw
:<GatewayIPv4>
-
Default gateway for IPv4 traffic.
-
gw6
:<GatewayIPv6>
-
Default gateway for IPv6 traffic.
-
hwaddr
:<XX:XX:XX:XX:XX:XX>
-
The interface MAC address. This is dynamically allocated by default, but you can set that statically if needed, for example to always have the same link-local IPv6 address. (lxc.network.hwaddr)
-
ip
:<IPv4Format/CIDR>
-
IPv4 address in CIDR format.
-
ip6
:<IPv6Format/CIDR>
-
IPv6 address in CIDR format.
-
mtu
:integer (64 - N)
-
Maximum transfer unit of the interface. (lxc.network.mtu)
-
name
:<string>
-
Name of the network device as seen from inside the container. (lxc.network.name)
-
rate
:<mbps>
-
Apply rate limiting to the interface
-
tag
:integer (1 - 4094)
-
VLAN tag for this interface.
-
trunks
:<vlanid[;vlanid...]>
-
VLAN ids to pass through the interface
-
type
:(veth)
-
Network interface type.
Managing Containers with pct
pct is the tool to manage Linux Containers on Proxmox VE. You can create and destroy containers, and control execution (start, stop, migrate, …). You can use pct to set parameters in the associated config file, like network configuration or memory limits.
CLI Usage Examples
Create a container based on a Debian template (provided you have already downloaded the template via the webgui)
pct create 100 /var/lib/vz/template/cache/debian-8.0-standard_8.0-1_amd64.tar.gz
Start container 100
pct start 100
Start a login session via getty
pct console 100
Enter the LXC namespace and run a shell as root user
pct enter 100
Display the configuration
pct config 100
Add a network interface called eth0, bridged to the host bridge vmbr0, set the address and gateway, while it’s running
pct set 100 -net0 name=eth0,bridge=vmbr0,ip=192.168.15.147/24,gw=192.168.15.1
Reduce the memory of the container to 512MB
pct set 100 -memory 512
Files
- /etc/pve/lxc/<CTID>.conf
-
Configuration file for the container <CTID>.
Container Advantages
-
Simple, and fully integrated into Proxmox VE. Setup looks similar to a normal VM setup.
-
Storage (ZFS, LVM, NFS, Ceph, …)
-
Network
-
Authentification
-
Cluster
-
-
Fast: minimal overhead, as fast as bare metal
-
High density (perfect for idle workloads)
-
REST API
-
Direct hardware access
Technology Overview
-
Integrated into Proxmox VE graphical user interface (GUI)
-
cgmanager for cgroup management
-
lxcfs to provive containerized /proc file system
-
apparmor
-
CRIU: for live migration (planned)
-
We use latest available kernels (4.4.X)
-
Image based deployment (templates)
-
Container setup from host (Network, DNS, Storage, …)