libcontainer

README

libcontainer - reference implementation for containers

Note on API changes:

Please bear with us while we work on making the libcontainer API stable and something that we can support long term. We are currently discussing the API with the community, therefore, if you currently depend on libcontainer please pin your dependency at a specific tag or commit id. Please join the discussion and help shape the API.

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 execution environment that shares the kernel of the host system and which is (optionally) isolated from other containers in the system.

libcontainer may be used to execute a process in a container. If a user tries to run a new process inside an existing container, the new process is added to the processes executing in the container.

Root file system

A container runs with a directory known as its root file system, or rootfs, mounted as the file system root. The rootfs is usually a full system tree.

Configuration

A container is initially configured by supplying configuration data when the container is created.

nsinit

nsinit is a cli application which demonstrates the use of libcontainer. It is able to spawn new containers or join existing containers, based on the current directory.

To use nsinit, cd into a Linux rootfs and copy a container.json file into the directory with your specified configuration. Environment, networking, and different capabilities for the container are specified in this file. The configuration is used for each process executed inside the container.

See the sample_configs folder for examples of what the container configuration should look like.

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

nsinit exec /bin/bash

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

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

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

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

Overview

Temporary API endpoint for libcontainer while the full API is finalized (api.go).

NOTE: The API is in flux and mainly not implemented. Proceed with caution until further notice.

Index

• func DeleteState(basePath string) error
• func SaveState(basePath string, state *State) error
• type Config
• type Container
• type ContainerStats
  • func GetStats(container *Config, state *State) (*ContainerStats, error)
• type Factory
• type MountConfig
• type Network
• type ProcessConfig
• type Route
• type RunState
• type State
  • func GetState(basePath string) (*State, error)

Functions

func DeleteState

func DeleteState(basePath string) error

DeleteState deletes the state.json file

func SaveState

func SaveState(basePath string, state *State) error

SaveState writes the container's runtime state to a state.json file in the specified path

Types

type Config

type Config struct {
	// Mount specific options.
	MountConfig *MountConfig `json:"mount_config,omitempty"`

	// Hostname optionally sets the container's hostname if provided
	Hostname string `json:"hostname,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"`

	// AppArmorProfile specifies the profile to apply to the process running in the container and is
	// change at the time the process is execed
	AppArmorProfile string `json:"apparmor_profile,omitempty"`

	// ProcessLabel specifies the label to apply to the process running in the container.  It is
	// commonly used by selinux
	ProcessLabel string `json:"process_label,omitempty"`

	// RestrictSys will remount /proc/sys, /sys, and mask over sysrq-trigger as well as /proc/irq and
	// /proc/bus
	RestrictSys bool `json:"restrict_sys,omitempty"`
}

Config defines configuration options for executing a process inside a contained environment.

type Container

type Container interface {
	// Returns the path to the container which contains the state
	Path() string

	// Returns the current run state of the container.
	//
	// Errors: container no longer exists,
	//         system error.
	RunState() (*RunState, error)

	// Returns the current config of the container.
	Config() *Config

	// Start a process inside the container. Returns the PID of the new process (in the caller process's namespace) and a channel that will return the exit status of the process whenever it dies.
	//
	// Errors: container no longer exists,
	//         config is invalid,
	//         container is paused,
	//         system error.
	Start(*ProcessConfig) (pid int, exitChan chan int, err error)

	// Destroys the container after killing all running processes.
	//
	// Any event registrations are removed before the container is destroyed.
	// No error is returned if the container is already destroyed.
	//
	// Errors: system error.
	Destroy() error

	// Returns the PIDs inside this container. The PIDs are in the namespace of the calling process.
	//
	// Errors: container no longer exists,
	//         system error.
	//
	// Some of the returned PIDs may no longer refer to processes in the Container, unless
	// the Container state is PAUSED in which case every PID in the slice is valid.
	Processes() ([]int, error)

	// Returns statistics for the container.
	//
	// Errors: container no longer exists,
	//         system error.
	Stats() (*ContainerStats, error)

	// If the Container state is RUNNING or PAUSING, sets the Container state to PAUSING and pauses
	// the execution of any user processes. Asynchronously, when the container finished being paused the
	// state is changed to PAUSED.
	// If the Container state is PAUSED, do nothing.
	//
	// Errors: container no longer exists,
	//         system error.
	Pause() error

	// If the Container state is PAUSED, resumes the execution of any user processes in the
	// Container before setting the Container state to RUNNING.
	// If the Container state is RUNNING, do nothing.
	//
	// Errors: container no longer exists,
	//         system error.
	Resume() error
}

A libcontainer container object.

Each container is thread-safe within the same process. Since a container can be destroyed by a separate process, any function may return that the container was not found.

type ContainerStats

type ContainerStats struct {
	NetworkStats *network.NetworkStats `json:"network_stats,omitempty"`
	CgroupStats  *cgroups.Stats        `json:"cgroup_stats,omitempty"`
}

func GetStats

func GetStats(container *Config, state *State) (*ContainerStats, error)

TODO(vmarmol): Complete Stats() in final libcontainer API and move users to that. DEPRECATED: The below portions are only to be used during the transition to the official API. Returns all available stats for the given container.

type Factory

type Factory interface {
	// Creates a new container in the given path. A unique ID is generated for the container and
	// starts the initial process inside the container.
	//
	// Returns the new container with a running process.
	//
	// Errors:
	// Path already exists
	// Config or initialConfig is invalid
	// System error
	//
	// On error, any partially created container parts are cleaned up (the operation is atomic).
	Create(path string, config *Config) (Container, error)

	// Load takes the path for an existing container and reconstructs the container
	// from the state.
	//
	// Errors:
	// Path does not exist
	// Container is stopped
	// System error
	Load(path string) (Container, error)
}

type MountConfig

type MountConfig mount.MountConfig

type Network

type Network network.Network

type ProcessConfig

type ProcessConfig struct {
	// The command to be run followed by any arguments.
	Args []string

	// Map of environment variables to their values.
	Env []string

	// Stdin is a pointer to a reader which provides the standard input stream.
	// Stdout is a pointer to a writer which receives the standard output stream.
	// Stderr is a pointer to a writer which receives the standard error stream.
	//
	// If a reader or writer is nil, the input stream is assumed to be empty and the output is
	// discarded.
	//
	// The readers and writers, if supplied, are closed when the process terminates. Their Close
	// methods should be idempotent.
	//
	// Stdout and Stderr may refer to the same writer in which case the output is interspersed.
	Stdin  io.ReadCloser
	Stdout io.WriteCloser
	Stderr io.WriteCloser
}

Configuration for a process to be run inside a container.

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.

type RunState

type RunState int

The running state of the container.

const (

	// The container exists and is running.
	Running RunState = iota

	// The container exists, it is in the process of being paused.
	Pausing

	// The container exists, but all its processes are paused.
	Paused

	// The container does not exist.
	Destroyed
)

type State

type State struct {
	// InitPid is the init process id in the parent namespace
	InitPid int `json:"init_pid,omitempty"`

	// InitStartTime is the init process start time
	InitStartTime string `json:"init_start_time,omitempty"`

	// Network runtime state.
	NetworkState network.NetworkState `json:"network_state,omitempty"`

	// Path to all the cgroups setup for a container. Key is cgroup subsystem name.
	CgroupPaths map[string]string `json:"cgroup_paths,omitempty"`
}

State represents a running container's state

func GetState

func GetState(basePath string) (*State, error)

GetState reads the state.json file for a running container