libcontainer

README

libcontainer - reference implementation for containers

Background

libcontainer specifies configuration options for what a container is. It provides a native Go implementation for using Linux namespaces with no external dependencies. libcontainer provides many convenience functions for working with namespaces, networking, and management.

Container

A container is a self contained directory that is able to run one or more processes without affecting the host system. The directory is usually a full system tree. Inside the directory a container.json file is placed with the runtime configuration for how the processes should be contained and run. Environment, networking, and different capabilities for the process are specified in this file. The configuration is used for each process executed inside the container.

See the container.json file for what the configuration should look like.

Using this configuration and the current directory holding the rootfs for a process, one can use libcontainer to exec the container. Running the life of the namespace, a pid file is written to the current directory with the pid of the namespaced process to the external world. A client can use this pid to wait, kill, or perform other operation with the container. If a user tries to run a new process inside an existing container with a live namespace, the namespace will be joined by the new process.

You may also specify an alternate root place where the container.json file is read and where the pid file will be saved.

nsinit

nsinit is a cli application used as the reference implementation of libcontainer. It is able to spawn or join new containers giving the current directory. To use nsinit cd into a Linux rootfs and copy a container.json file into the directory with your specified configuration.

To execute /bin/bash in the current directory as a container just run:

nsinit exec /bin/bash

If you wish to spawn another process inside the container while your current bash session is running just run the exact same command again to get another bash shell or change the command. If the original process dies, PID 1, all other processes spawned inside the container will also be killed and the namespace will be removed.

You can identify if a process is running in a container by looking to see if pid is in the root of the directory.

Future

See the roadmap.

Copyright and license

Code and documentation copyright 2014 Docker, inc. Code released under the Apache 2.0 license. Docs released under Creative commons.

Hacking on libcontainer

First of all, please familiarise yourself with the libcontainer Principles.

If you're a contributor or aspiring contributor, you should read the Contributors' Guide.

If you're a maintainer or aspiring maintainer, you should read the Maintainers' Guide and "How can I become a maintainer?" in the Contributors' Guide.

Documentation

Index

• Variables
• func GetAllCapabilities() []string
• type Capabilities
  • func (c Capabilities) Contains(capp string) bool
  • func (c Capabilities) Get(capp string) *Capability
• type Capability
  • func GetCapability(key string) *Capability
  • func (c *Capability) String() string
• type Container
• type Context
• type Mount
• type Mounts
  • func (s Mounts) OfType(t string) Mounts
• type Namespace
  • func GetNamespace(key string) *Namespace
  • func (ns *Namespace) String() string
• type Namespaces
  • func (n Namespaces) Contains(ns string) bool
  • func (n Namespaces) Get(ns string) *Namespace
• type Network
• type Route

Variables

var (
	ErrUnkownNamespace  = errors.New("Unknown namespace")
	ErrUnkownCapability = errors.New("Unknown capability")
	ErrUnsupported      = errors.New("Unsupported method")
)

Functions

func GetAllCapabilities

func GetAllCapabilities() []string

Types

type Capabilities

type Capabilities []*Capability

func (Capabilities) Contains

func (c Capabilities) Contains(capp string) bool

Contains returns true if the specified Capability is in the slice

func (Capabilities) Get

func (c Capabilities) Get(capp string) *Capability

type Capability

type Capability struct {
	Key   string         `json:"key,omitempty"`
	Value capability.Cap `json:"value,omitempty"`
}

func GetCapability

func GetCapability(key string) *Capability

func (*Capability) String

func (c *Capability) String() string

type Container

type Container struct {
	// Hostname optionally sets the container's hostname if provided
	Hostname string `json:"hostname,omitempty"`

	// ReadonlyFs will remount the container's rootfs as readonly where only externally mounted
	// bind mounts are writtable
	ReadonlyFs bool `json:"readonly_fs,omitempty"`

	// NoPivotRoot will use MS_MOVE and a chroot to jail the process into the container's rootfs
	// This is a common option when the container is running in ramdisk
	NoPivotRoot bool `json:"no_pivot_root,omitempty"`

	// User will set the uid and gid of the executing process running inside the container
	User string `json:"user,omitempty"`

	// WorkingDir will change the processes current working directory inside the container's rootfs
	WorkingDir string `json:"working_dir,omitempty"`

	// Env will populate the processes environment with the provided values
	// Any values from the parent processes will be cleared before the values
	// provided in Env are provided to the process
	Env []string `json:"environment,omitempty"`

	// Tty when true will allocate a pty slave on the host for access by the container's process
	// and ensure that it is mounted inside the container's rootfs
	Tty bool `json:"tty,omitempty"`

	// Namespaces specifies the container's namespaces that it should setup when cloning the init process
	// If a namespace is not provided that namespace is shared from the container's parent process
	Namespaces map[string]bool `json:"namespaces,omitempty"`

	// Capabilities specify the capabilities to keep when executing the process inside the container
	// All capbilities not specified will be dropped from the processes capability mask
	Capabilities []string `json:"capabilities,omitempty"`

	// Networks specifies the container's network setup to be created
	Networks []*Network `json:"networks,omitempty"`

	// Routes can be specified to create entries in the route table as the container is started
	Routes []*Route `json:"routes,omitempty"`

	// Cgroups specifies specific cgroup settings for the various subsystems that the container is
	// placed into to limit the resources the container has available
	Cgroups *cgroups.Cgroup `json:"cgroups,omitempty"`

	// Context is a generic key value format that allows for additional settings to be passed
	// on the container's creation
	// This is commonly used to specify apparmor profiles, selinux labels, and different restrictions
	// placed on the container's processes
	Context Context `json:"context,omitempty"`

	// Mounts specify additional source and destination paths that will be mounted inside the container's
	// rootfs and mount namespace if specified
	Mounts Mounts `json:"mounts,omitempty"`

	// The device nodes that should be automatically created within the container upon container start.  Note, make sure that the node is marked as allowed in the cgroup as well!
	DeviceNodes []*devices.Device `json:"device_nodes,omitempty"`
}

Container defines configuration options for executing a process inside a contained environment

type Context

type Context map[string]string

Context is a generic key value pair that allows arbatrary data to be sent

type Mount

type Mount struct {
	Type        string `json:"type,omitempty"`
	Source      string `json:"source,omitempty"`      // Source path, in the host namespace
	Destination string `json:"destination,omitempty"` // Destination path, in the container
	Writable    bool   `json:"writable,omitempty"`
	Private     bool   `json:"private,omitempty"`
}

type Mounts

type Mounts []Mount

func (Mounts) OfType

func (s Mounts) OfType(t string) Mounts

type Namespace

type Namespace struct {
	Key   string `json:"key,omitempty"`
	Value int    `json:"value,omitempty"`
	File  string `json:"file,omitempty"`
}

func GetNamespace

func GetNamespace(key string) *Namespace

func (*Namespace) String

func (ns *Namespace) String() string

type Namespaces

type Namespaces []*Namespace

func (Namespaces) Contains

func (n Namespaces) Contains(ns string) bool

Contains returns true if the specified Namespace is in the slice

func (Namespaces) Get

func (n Namespaces) Get(ns string) *Namespace

type Network

type Network struct {
	// Type sets the networks type, commonly veth and loopback
	Type string `json:"type,omitempty"`

	// Context is a generic key value format for setting additional options that are specific to
	// the network type
	Context Context `json:"context,omitempty"`

	// Address contains the IP and mask to set on the network interface
	Address string `json:"address,omitempty"`

	// Gateway sets the gateway address that is used as the default for the interface
	Gateway string `json:"gateway,omitempty"`

	// Mtu sets the mtu value for the interface and will be mirrored on both the host and
	// container's interfaces if a pair is created, specifically in the case of type veth
	Mtu int `json:"mtu,omitempty"`
}

Network defines configuration for a container's networking stack

The network configuration can be omited from a container causing the container to be setup with the host's networking stack

type Route

type Route struct {
	// Sets the destination and mask, should be a CIDR.  Accepts IPv4 and IPv6
	Destination string `json:"destination,omitempty"`

	// Sets the source and mask, should be a CIDR.  Accepts IPv4 and IPv6
	Source string `json:"source,omitempty"`

	// Sets the gateway.  Accepts IPv4 and IPv6
	Gateway string `json:"gateway,omitempty"`

	// The device to set this route up for, for example: eth0
	InterfaceName string `json:"interface_name,omitempty"`
}

Routes can be specified to create entries in the route table as the container is started

All of destination, source, and gateway should be either IPv4 or IPv6. One of the three options must be present, and ommitted entries will use their IP family default for the route table. For IPv4 for example, setting the gateway to 1.2.3.4 and the interface to eth0 will set up a standard destination of 0.0.0.0(or *) when viewed in the route table.