layout: post title: LinuxKit date: 2017-04-19 11:09:53

tags: [docker]

LinuxKit是Docker最新发布的一个用于为容器构建安全、便携、可移植操作系统的工具包。它根据用户编写的yaml(指定kernel和基于docker image的一些列服务)自动构建一个常见虚拟化平台或云平台的虚拟机镜像,并自动运行起来。主要特性包括

安装

git clone https://github.com/linuxkit/linuxkit $GOPATH/src/github.com/linuxkit/linuxkit
make && make install

原理

编写yaml

LinuxKit需要编写一个yaml文件,来配置所需要的服务。可选的配置包括

比如一个简单的nginx服务为

kernel:
  image: "mobylinux/kernel:4.9.x"
  cmdline: "console=ttyS0 console=tty0 page_poison=1"
init:
  - linuxkit/init:42fe8cb1508b3afed39eb89821906e3cc7a70551
  - mobylinux/runc:b0fb122e10dbb7e4e45115177a61a3f8d68c19a9
  - linuxkit/containerd:60e2486a74c665ba4df57e561729aec20758daed
  - mobylinux/ca-certificates:eabc5a6e59f05aa91529d80e9a595b85b046f935
onboot:
  - name: sysctl
    image: "mobylinux/sysctl:2cf2f9d5b4d314ba1bfc22b2fe931924af666d8c"
    net: host
    pid: host
    ipc: host
    capabilities:
     - CAP_SYS_ADMIN
    readonly: true
  - name: binfmt
    image: "linuxkit/binfmt:8881283ac627be1542811bd25c85e7782aebc692"
    binds:
     - /proc/sys/fs/binfmt_misc:/binfmt_misc
    readonly: true
  - name: dhcpcd
    image: "linuxkit/dhcpcd:48e249ebef6a521eed886b3bce032db69fbb4afa"
    binds:
     - /var:/var
     - /tmp/etc:/etc
    capabilities:
     - CAP_NET_ADMIN
     - CAP_NET_BIND_SERVICE
     - CAP_NET_RAW
    net: host
    command: ["/sbin/dhcpcd", "--nobackground", "-f", "/dhcpcd.conf", "-1"]
services:
  - name: rngd
    image: "mobylinux/rngd:3dad6dd43270fa632ac031e99d1947f20b22eec9"
    capabilities:
     - CAP_SYS_ADMIN
    oomScoreAdj: -800
    readonly: true
  - name: nginx
    image: "nginx:alpine"
    capabilities:
     - CAP_NET_BIND_SERVICE
     - CAP_CHOWN
     - CAP_SETUID
     - CAP_SETGID
     - CAP_DAC_OVERRIDE
    net: host
files:
  - path: etc/docker/daemon.json
    contents: '{"debug": true}'
trust:
  image:
    - mobylinux/kernel
outputs:
  - format: kernel+initrd
  - format: iso-bios
  - format: iso-efi

构建

$ moby build linuxkit.yml
Extract kernel image: mobylinux/kernel:4.9.x
Add init containers:
Process init image: linuxkit/init:42fe8cb1508b3afed39eb89821906e3cc7a70551
Process init image: mobylinux/runc:b0fb122e10dbb7e4e45115177a61a3f8d68c19a9
Process init image: linuxkit/containerd:60e2486a74c665ba4df57e561729aec20758daed
Process init image: mobylinux/ca-certificates:eabc5a6e59f05aa91529d80e9a595b85b046f935
Add onboot containers:
  Create OCI config for mobylinux/sysctl:2cf2f9d5b4d314ba1bfc22b2fe931924af666d8c
  Create OCI config for linuxkit/binfmt:8881283ac627be1542811bd25c85e7782aebc692
  Create OCI config for linuxkit/dhcpcd:48e249ebef6a521eed886b3bce032db69fbb4afa
Add service containers:
  Create OCI config for mobylinux/rngd:3dad6dd43270fa632ac031e99d1947f20b22eec9
  Create OCI config for nginx:alpine
Add files:
  etc/docker/daemon.json
Create outputs:
  linuxkit-bzImage linuxkit-initrd.img linuxkit-cmdline
  linuxkit.iso
  linuxkit-efi.iso

编译完成后的文件大约58M。

$ ls -lh linuxkit*
-rw-r--r-- 1 root root 6.7M Apr 19 02:39 linuxkit-bzImage
-rw-r--r-- 1 root root   40 Apr 19 02:39 linuxkit-cmdline
-rw-r--r-- 1 root root  58M Apr 19 02:40 linuxkit-efi.iso
-rw-r--r-- 1 root root  50M Apr 19 02:39 linuxkit-initrd.img
-rw-r--r-- 1 root root  57M Apr 19 02:39 linuxkit.iso
-rw-r--r-- 1 root root 1.6K Apr 19 02:19 linuxkit.yml

运行

LinuxKit目前支持在gcp/hyperkit/qemu/vmware/packet/Hyper-V等多个平台上运行。比如用qemu的方式运行:

$ moby run qemu linuxkit
....

默认运行后会自动进入VM的console:

/ # pstree
init-+-containerd---containerd-shim---nginx---nginx
     |-containers---ctr
     |-sh---pstree
     `-sh

参考文档

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