X-Git-Url: https://git.proxmox.com/?p=pve-docs.git;a=blobdiff_plain;f=pct.adoc;h=2d52ad2b5fa6d92385c4e4ad712a8f1b603eeb47;hp=611ff484b9c7bf0272e2dcdc97373cbf788340ed;hb=04c569f66d62b615840b27f791481b8bc3e5696e;hpb=38fd0958719a329859b3d0d719c37d5df15a2d8d diff --git a/pct.adoc b/pct.adoc index 611ff48..2d52ad2 100644 --- a/pct.adoc +++ b/pct.adoc @@ -24,17 +24,389 @@ Proxmox Container Toolkit include::attributes.txt[] endif::manvolnum[] -'pct' is a tool to manages Linux Containers (LXC). You can create and -destroy containers, and control execution -(start/stop/suspend/resume). Besides that, you can use pct to set -parameters in the associated config file, like network configuration -or memory. + +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. + +{pve} uses https://linuxcontainers.org/[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 {pve}. 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 {pve} +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". + +NOTE: If you want to run micro-containers (with docker, rct, ...), 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/.conf' file stores container configuration, +where '' 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. + +NOTE: CTIDs < 100 are reserved for internal purposes, and CTIDs need to be +unique cluster wide. + +.Example Container Configuration +---- +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: + +.Container Configuration with Snapshot +---- +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 + +The above task depends on the OS type, so the implementation is different +for each OS type. You can also disable any 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 + +NOTE: Container start fails if the configured 'ostype' differs from the auto +detected type. + + +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 {pve} Appliance Manager) command line utility. You can also +download https://www.turnkeylinux.org/[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: + +.List available 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 {pve} volume identifiers. They include +the storage name, and most other {pve} 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 {pve} 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. + +Container Mountpoints +--------------------- + +Beside the root directory the container can also have additional mountpoints. +Currently there are basically three types of mountpoints: storage backed +mountpoints, bind mounts and device mounts. + +Storage backed mountpoints are managed by the {pve} 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. + +WARNING: 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 +mountpoint to make it accessible inside the container. + +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 mountpoint: `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. + +NOTE: You need to run the above commands for every mountpoint by passing +the mountpoint'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 +----------------- + +TODO + + +Managing Containers with 'pct' +------------------------------ + +'pct' is the tool to manage Linux Containers on {pve}. 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 downloaded -the template via the webgui before) +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 @@ -66,9 +438,9 @@ Reduce the memory of the container to 512MB Files ------ -'/etc/pve/lxc/.conf':: +'/etc/pve/lxc/.conf':: -Configuration file for the container +Configuration file for the container ''. Container Advantages @@ -109,9 +481,9 @@ Technology Overview - CRIU: for live migration (planned) -- We use latest available kernels (4.2.X) +- We use latest available kernels (4.4.X) -- image based deployment (templates) +- Image based deployment (templates) - Container setup from host (Network, DNS, Storage, ...)