pkg/libcontainer
Alexander Larsson 83de20deb7 libcontainer: Use pivot_root instead of chroot
Instead of keeping all the old mounts in the container namespace and
just using subtree as root we pivot_root so that the actual root in
the namespace is the root we want, and then we unmount the previous
mounts.

This has multiple advantages:

* The namespace mount tree is smaller (in the kernel)
* If you break out of the chroot you could previously access the host
  filesystem. Now the host filesystem is fully invisible to the namespace.
* We get rid of all unrelated mounts from the parent namespace, which means
  we don't hog these. This is important if we later switch to MS_PRIVATE instead
  of MS_SLAVE as otherwise these mounts would be impossible to unmount from the
  parent namespace.

Docker-DCO-1.1-Signed-off-by: Alexander Larsson <alexl@redhat.com> (github: alexlarsson)
2014-03-04 12:44:08 +01:00
..
capabilities Better capability/namespace management 2014-02-24 21:52:29 -08:00
network Code review updates 2014-02-26 19:21:46 -08:00
nsinit libcontainer: Use pivot_root instead of chroot 2014-03-04 12:44:08 +01:00
utils Refactor and improve libcontainer and driver 2014-02-24 21:11:52 -08:00
container.go Make network a slice to support multiple types 2014-02-26 14:20:41 -08:00
container.json Make network a slice to support multiple types 2014-02-26 14:20:41 -08:00
MAINTAINERS Initial commit of libcontainer 2014-02-21 14:56:15 -08:00
README.md very minor spelling 2014-03-04 10:12:12 +10:00
TODO.md Update readme and add TODO 2014-02-21 14:56:16 -08:00
types.go Fix cross compile for make cross 2014-02-25 15:19:13 -08:00
types_linux.go Fix cross compile for make cross 2014-02-25 15:19:13 -08:00

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 convience 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 ran. Environment, networking, and different capabilities for the process are specified in this file. The configuration is used for each process executed inside the container.

Sample container.json file:

{
    "hostname": "koye",
    "tty": true,
    "environment": [
        "HOME=/",
        "PATH=PATH=$PATH:/bin:/usr/bin:/sbin:/usr/sbin",
        "container=docker",
        "TERM=xterm-256color"
    ],
    "namespaces": [
        "NEWIPC",
        "NEWNS",
        "NEWPID",
        "NEWUTS",
        "NEWNET"
    ],
    "capabilities": [
        "SETPCAP",
        "SYS_MODULE",
        "SYS_RAWIO",
        "SYS_PACCT",
        "SYS_ADMIN",
        "SYS_NICE",
        "SYS_RESOURCE",
        "SYS_TIME",
        "SYS_TTY_CONFIG",
        "MKNOD",
        "AUDIT_WRITE",
        "AUDIT_CONTROL",
        "MAC_OVERRIDE",
        "MAC_ADMIN",
        "NET_ADMIN"
    ],
    "networks": [{
            "type": "veth",
            "context": {
                "bridge": "docker0",
                "prefix": "dock"
            },
            "address": "172.17.0.100/16",
            "gateway": "172.17.42.1",
            "mtu": 1500
        }
    ],
    "cgroups": {
        "name": "docker-koye",
        "parent": "docker",
        "memory": 5248000
    }
}

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 an 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.