CoreOS是一种专门为运行类docker容器而生的linux发行版。与其他通用linux发行版(ubuntudebianredhat)相 比,它具有体型最小,消耗最小,支持滚动更新等特点。除此之外CoreOS内置的分布式系统服务组件也给开发者和运维者组建分布式集群、部署分布式服务应 用带来了极大便利。

CoreOS与知名容器Docker脚前脚后诞生,到目前为止已经较为成熟,国外主流云平台提供商如Amazon EC2Google Compute EngineMicrosoft AzureDigtial Ocean等均提供了CoreOS image,通过这些服务,你可以一键建立一个CoreOS实例,这似乎也是CoreOS官方推荐的主流install方式(最Easy)。

CoreOS当然支持其他方式的安装,比如支持虚拟机安装(vagrant+virtualbox)、PXE(preboot execute environment)安装以及iso install to 物理disk方式。如果仅仅是做一些实验,虚拟机安装是最简单也是最安全的方式。不过由于CoreOS的官方下载站在大陆无法直接访问(大陆程序员们好悲 催啊),因此这一最简单的虚拟机安装CoreOS的过程也就不那么简单了。

通过core-vagrant安装的直接结果是CoreOS被安装到一个VirtualBox虚拟机中,之后我们利用Vagrant命令来进行 CoreOS虚拟机的启停。CoreOS以及Vagrant都在持续演进,尤其是CoreOS目前在active dev中,版本号变化很快,这也是CoreOS滚动升级的必然结果。因此在安装操作演示前,我们有必要明确一下这个安装过程使用的软件版本:

    物理机OS:
        Ubuntu 12.04 3.8.0-42-generic x86_64
    VirtualBox:
        Oracle VM VirtualBox Manager 4.2.10
    Vagrant:
        Vagrant 1.7.3

    CoreOS:
        stable 717.3.0

    coreos-vagrant source:
        commit b9ed7e2182ff08b72419ab3e89f4a5652bc75082

一、原理

如果没有Wall,CoreOS的coreos-vagrant安装将非常简单:

1、git clone https://github.com/coreos/coreos-vagrant
2、编辑配置文件
3、vagrant up
4、vagrant ssh

但是现在有了Wall,步骤3:vagrant up会报错:无法连接到http://stable.release.core-os.net/amd64-usr/717.3.0/xx这个url,导致安装失败。

我大致分析了一下vagrant up的执行过程:

1、设置配置默认值

    $num_instances = 1
    $instance_name_prefix = "core"
    $update_channel = "alpha"
    $image_version = "current"
    $enable_serial_logging = false
    $share_home = false
    $vm_gui = false
    $vm_memory = 1024
    $vm_cpus = 1
    $shared_folders = {}
    $forwarded_ports = {}

2、判断是否存在config.rb这个配置,如果有,则加载。
3、设置config.vm.url,并获取对应的json文件:

{
  "name": "coreos-stable",
  "description": "CoreOS stable",
  "versions": [{
    "version": "717.3.0",
    "providers": [{
      "name": "virtualbox",
      "url": "http://stable.release.core-os.net/amd64-usr/717.3.0/coreos_production_vagrant.box",
      "checksum_type": "sha256",
      "checksum": "99dcd74c7cae8b1d90f108f8819f92b17bfbd34f4f141325bd0400fe4def55b6"
    }]
  }]
}

4、根据config.vm.provider(是virtualbox还是vmvare等)来决定采用哪种虚拟机创建逻辑。

这里我们看到,整个过程只需要从core-os.net下载两个文件:coreos_production_vagrant.boxcoreos_production_vagrant.json。如果我们提前将这两个文件下载到本地,并放在一个临时的http server下,修改Vagrantfile和coreos_production_vagrant.json这两个文件,就应该可以通过coreos-vagrant安装了。

二、coreos-vagrant安装single instance CoreOS

好了,根据上述原理,我们首先要下载coreos_production_vagrant.boxcoreos_production_vagrant.json这两个文件,根据我们的channel和版本选择,两个文件的下载地址分别为:

 http://stable.release.core-os.net/amd64-usr/717.3.0/coreos_production_vagrant.box
 http://stable.release.core-os.net/amd64-usr/717.3.0/coreos_production_vagrant.json

接下来就是不管你用什么梯子,只要把这两个文件下载到本地,并放到一个目录下就好了。

我们需要修改一下coreos_production_vagrant.json,将其中的url改为:
   
    "url": "http://localhost:8080/coreos_production_vagrant.box"

我们要将这两个文件放到一个local file server中,后续供core-vagrant访问。最简单的方法就是使用:

    python -m SimpleHTTPServer 8080

当然使用Go实现一个简单的http file server也是非常简单的:

//fileserver.go
package main

import "net/http"
import "log"

func main() {
    log.Fatal(http.ListenAndServe(":8080", http.FileServer(http.Dir("./"))))
}

接下来我们就可以按照正常步骤,下载coreos-vagrant并up了:

$git clone https://github.com/coreos/coreos-vagrant

修改Vagrantfile:

$ diff Vagrantfile Vagrantfile.bak
14,15c14,15
< $update_channel = "stable"
< $image_version = "717.3.0"

> $update_channel = "alpha"
> $image_version = "current"
55c55
<   config.vm.box_url = "http://localhost:8080/coreos_production_vagrant.json"

>   config.vm.box_url = "http://%s.release.core-os.net/amd64-usr/%s/coreos_production_vagrant.json" % [$update_channel, $image_version]

将user-data.sample改名为user-data,并编辑user-data,在etcd2下面增加一行:

      etcd2:
    name: core-01

将units:下面对于etcd2的注释去掉,以enable etcd2服务。(将etcd服务注释掉)

万事俱备,只需vagrant up。

$ vagrant up
Bringing machine 'core-01' up with 'virtualbox' provider…
==> core-01: Box 'coreos-stable' could not be found. Attempting to find and install…
    core-01: Box Provider: virtualbox
    core-01: Box Version: 717.3.0
==> core-01: Loading metadata for box 'http://localhost:8080/coreos_production_vagrant.json'
    core-01: URL: http://localhost:8080/coreos_production_vagrant.json
==> core-01: Adding box 'coreos-stable' (v717.3.0) for provider: virtualbox
    core-01: Downloading: http://localhost:8080/coreos_production_vagrant.box
    core-01: Calculating and comparing box checksum…
==> core-01: Successfully added box 'coreos-stable' (v717.3.0) for 'virtualbox'!
==> core-01: Importing base box 'coreos-stable'…
==> core-01: Matching MAC address for NAT networking…
==> core-01: Checking if box 'coreos-stable' is up to date…
==> core-01: Setting the name of the VM: coreos-vagrant_core-01_1437121834188_89503
==> core-01: Clearing any previously set network interfaces…
==> core-01: Preparing network interfaces based on configuration…
    core-01: Adapter 1: nat
    core-01: Adapter 2: hostonly
==> core-01: Forwarding ports…
    core-01: 22 => 2222 (adapter 1)
==> core-01: Running 'pre-boot' VM customizations…
==> core-01: Booting VM…
==> core-01: Waiting for machine to boot. This may take a few minutes…
    core-01: SSH address: 127.0.0.1:2222
    core-01: SSH username: core
    core-01: SSH auth method: private key
    core-01: Warning: Connection timeout. Retrying…
==> core-01: Machine booted and ready!
==> core-01: Setting hostname…
==> core-01: Configuring and enabling network interfaces…
==> core-01: Running provisioner: file…
==> core-01: Running provisioner: shell…
    core-01: Running: inline script

登入你的coreos实例:
$ vagrant ssh
CoreOS stable (717.3.0)
core@core-01 ~ $

在vagrant up时,你可能会遇到如下两个错误:

错误1:

Progress state: VBOX_E_FILE_ERROR
VBoxManage: error: Could not open the medium storage unit '/home1/tonybai/.vagrant.d/boxes/coreos-stable/717.3.0/virtualbox/coreos_production_vagrant_image.vmdk'.
VBoxManage: error: VMDK: inconsistent references to grain directory in '/home1/tonybai/.vagrant.d/boxes/coreos-stable/717.3.0/virtualbox/coreos_production_vagrant_image.vmdk'  (VERR_VD_VMDK_INVALID_HEADER).

这个问题的原因很可能是你的Virtualbox版本不对,比如版本太低,与coreos_production_vagrant.box格式不兼容。可尝试安装一下高版本virtualbox来解决。

错误2:

core-01: SSH address: 127.0.0.1:2222
core-01: SSH username: core
core-01: SSH auth method: private key
core-01: Warning: Connection timeout. Retrying…
core-01: Warning: Connection timeout. Retrying…
core-01: Warning: Connection timeout. Retrying…

coreos虚拟机创建后,似乎一直无法连接上。在coreos的github issue中,有人遇到了这个问题,目前给出的原因是因为cpu的支持虚拟化技术的vt开关没有打开,需要在bios中将其开启。这主要在安装64bit box时才会发生。

到这里,我们已经完成了一个single instance coreos虚拟机的安装。vagrant halt可以帮助你将启动的coreos虚拟机停下来。

$ vagrant halt
==> core-01: Attempting graceful shutdown of VM…

三、  CoreOS cluster

上面虽然成功的安装了coreos,然并卵。在实际应用中,CoreOS多以Cluster形式呈现,也就是说我们要启动多个CoreOS实例。

使用vagrant启动多个coreos实例很简单,只需将配置中的$num_instances从1改为n。

这里我们启用config.rb这个配置文件(将config.rb.sample改名为config.rb),并将其中的$num_instances修改为3:

# Size of the CoreOS cluster created by Vagrant
$num_instances=3

该配置文件中的数据会覆盖Vagrantfile中的默认配置。

三个instance中的etcd2要想组成集群还需要一个配置修改,那就是在etcd.io上申请一个token:

$curl https://discovery.etcd.io/new

https://discovery.etcd.io/fe81755687323aae273dc5f111eb059a

将这个token配置到user-data中的etcd2下:

  etcd2:

    #generate a new token for each unique cluster from https://discovery.etcd.io/new
    #discovery: https://discovery.etcd.io/<token>
    discovery: https://discovery.etcd.io/fe81755687323aae273dc5f111eb059a

我们再来up看看:

$ vagrant up
Bringing machine 'core-01' up with 'virtualbox' provider…
Bringing machine 'core-02' up with 'virtualbox' provider…
Bringing machine 'core-03' up with 'virtualbox' provider…
==> core-01: Checking if box 'coreos-stable' is up to date…
==> core-01: VirtualBox VM is already running.
==> core-02: Importing base box 'coreos-stable'…
==> core-02: Matching MAC address for NAT networking…
==> core-02: Checking if box 'coreos-stable' is up to date…
==> core-02: Setting the name of the VM: coreos-vagrant_core-02_1437388468647_96550
==> core-02: Fixed port collision for 22 => 2222. Now on port 2200.
==> core-02: Clearing any previously set network interfaces…
==> core-02: Preparing network interfaces based on configuration…
    core-02: Adapter 1: nat
    core-02: Adapter 2: hostonly
==> core-02: Forwarding ports…
    core-02: 22 => 2200 (adapter 1)
==> core-02: Running 'pre-boot' VM customizations…
==> core-02: Booting VM…
==> core-02: Waiting for machine to boot. This may take a few minutes…
    core-02: SSH address: 127.0.0.1:2200
    core-02: SSH username: core
    core-02: SSH auth method: private key
    core-02: Warning: Connection timeout. Retrying…
==> core-02: Machine booted and ready!
==> core-02: Setting hostname…
==> core-02: Configuring and enabling network interfaces…
==> core-02: Running provisioner: file…
==> core-02: Running provisioner: shell…
    core-02: Running: inline script
==> core-03: Importing base box 'coreos-stable'…
==> core-03: Matching MAC address for NAT networking…
==> core-03: Checking if box 'coreos-stable' is up to date…
==> core-03: Setting the name of the VM: coreos-vagrant_core-03_1437388512743_68112
==> core-03: Fixed port collision for 22 => 2222. Now on port 2201.
==> core-03: Clearing any previously set network interfaces…
==> core-03: Preparing network interfaces based on configuration…
    core-03: Adapter 1: nat
    core-03: Adapter 2: hostonly
==> core-03: Forwarding ports…
    core-03: 22 => 2201 (adapter 1)
==> core-03: Running 'pre-boot' VM customizations…
==> core-03: Booting VM…
==> core-03: Waiting for machine to boot. This may take a few minutes…
    core-03: SSH address: 127.0.0.1:2201
    core-03: SSH username: core
    core-03: SSH auth method: private key
    core-03: Warning: Connection timeout. Retrying…
==> core-03: Machine booted and ready!
==> core-03: Setting hostname…
==> core-03: Configuring and enabling network interfaces…
==> core-03: Running provisioner: file…
==> core-03: Running provisioner: shell…
    core-03: Running: inline script

$vagrant ssh core-02
CoreOS stable (717.3.0)
core@core-02 ~ $

可以看到Vagrant启动了三个coreos instance。关闭这些instance,同样用halt:

$ vagrant halt
==> core-03: Attempting graceful shutdown of VM…
==> core-02: Attempting graceful shutdown of VM…
==> core-01: Attempting graceful shutdown of VM…

四、小结

以上仅仅是CoreOS最基本的入门,虽然现在安装ok了,但CoreOS的各种服务组件的功用、配置;如何与Docker配合形成分布式服务系统;如何用Google Kubernetes管理容器集群等还需更进一步深入学习,这个后续会慢慢道来。