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理解Docker(1):Docker安装和基础用法详细介绍

原作者: [db:作者] 来自: [db:来源] 收藏 邀请

Docker是一个用了一种新颖方式实现的超轻量虚拟机,在实现的原理和应用上还是和VM有巨大差别,专业的叫法是应用容器(Application Container)。(我个人还是喜欢称虚拟机)

1. 安装

1.1 在 Ubuntu 14.04 上安装 Docker

前提要求:

内核版本必须是3.10或者以上

依次执行下面的步骤:

sudo apt-get update
sudo apt-get install apt-transport-https ca-certificates
sudo apt-key adv --keyserver hkp://p80.pool.sks-keyservers.net:80 --recv-keys 58118E89F3A912897C070ADBF76221572C52609D
编辑 /etc/apt/sources.list.d/docker.list 文件,添加 deb https://apt.dockerproject.org/repo ubuntu-trusty main
sudo apt-get update
sudo apt-get purge lxc-docker
apt-cache policy docker-engine
apt-get upgrade
sudo apt-get install linux-image-extra-$(uname -r) linux-image-extra-virtual
sudo apt-get install docker-engine

至此,安装过程完成。

运行 sudo service docker start 启动 Docker 守护进程。

运行 docker version 查看 Docker 版本

root@devstack:/home/sammy# docker --version
Docker version 1.12.1, build 23cf638

启动第一个容器:

启动第一个Docker 容器 docker run hello-world

root@devstack:/home/sammy# docker run hello-world

Hello from Docker!
This message shows that your installation appears to be working correctly.

它的运行成功也表明前面的安装步骤都运行正确了。

以上内容参考自 Docker 官网:https://docs.docker.com/engine/installation/linux/ubuntulinux/

1.2 Docker 到目前(2016/09/16)为止的版本历史

2. Docker 的基本操作

2.1 Docker 容器的状态机

一个容器在某个时刻可能处于以下几种状态之一:

  • created:已经被创建 (使用 docker ps -a 命令可以列出)但是还没有被启动 (使用 docker ps 命令还无法列出)
  • running:运行中
  • paused:容器的进程被暂停了
  • restarting:容器的进程正在重启过程中
  • exited:上图中的 stopped 状态,表示容器之前运行过但是现在处于停止状态(要区别于 created 状态,它是指一个新创出的尚未运行过的容器)。可以通过 start 命令使其重新进入 running 状态
  • destroyed:容器被删除了,再也不存在了

你可以在 docker inspect 命令的输出中查看其详细状态:

"State": {
   "Status": "running",
   "Running": true,
   "Paused": false,
   "Restarting": false,
   "OOMKilled": false,
   "Dead": false,
   "Pid": 4597,
   "ExitCode": 0,
   "Error": "",
   "StartedAt": "2016-09-16T08:09:34.53403504Z",
   "FinishedAt": "2016-09-16T08:06:44.365106765Z"
  }

2.2 Docker 命令概述

我们可以把Docker 的命令大概地分类如下:

镜像操作:
 build  Build an image from a Dockerfile
 commit Create a new image from a container's changes
 images List images
 load  Load an image from a tar archive or STDIN
 pull  Pull an image or a repository from a registry
 push  Push an image or a repository to a registry
 rmi  Remove one or more images
 search Search the Docker Hub for images
 tag  Tag an image into a repository
 save  Save one or more images to a tar archive (streamed to STDOUT by default)
 history 显示某镜像的历史
 inspect 获取镜像的详细信息

 容器及其中应用的生命周期操作:
 create Create a new container (创建一个容器)  
 kill  Kill one or more running containers
 inspect Return low-level information on a container, image or task
 pause  Pause all processes within one or more containers
 ps  List containers
 rm  Remove one or more containers (删除一个或者多个容器)
 rename Rename a container
 restart Restart a container
 run  Run a command in a new container (创建并启动一个容器)
 start  Start one or more stopped containers (启动一个处于停止状态的容器)
 stats  Display a live stream of container(s) resource usage statistics (显示容器实时的资源消耗信息)
 stop  Stop one or more running containers (停止一个处于运行状态的容器)
 top  Display the running processes of a container
 unpause Unpause all processes within one or more containers
 update Update configuration of one or more containers
 wait  Block until a container stops, then print its exit code
 attach Attach to a running container
 exec  Run a command in a running container
 port  List port mappings or a specific mapping for the container
 logs  获取容器的日志 
 
 容器文件系统操作:
 cp  Copy files/folders between a container and the local filesystem
 diff  Inspect changes on a container's filesystem
 export Export a container's filesystem as a tar archive
 import Import the contents from a tarball to create a filesystem image
 
 Docker registry 操作:
 login  Log in to a Docker registry.
 logout Log out from a Docker registry.
 
 Volume 操作
 volume Manage Docker volumes
 
 网络操作
 network Manage Docker networks
 
 Swarm 相关操作
 swarm  Manage Docker Swarm
 service Manage Docker services
 node  Manage Docker Swarm nodes  
 
 系统操作: 
 version Show the Docker version information
 events Get real time events from the server (持续返回docker 事件)
 info  Display system-wide information (显示Docker 主机系统范围内的信息)

比较有意思的几个命令:

(1)容器从生到死整个生命周期

root@devstack:/home/sammy# docker create --name web31 training/webapp python app.py #创建名字为 web31 的容器
7465f4cb7c49555af32929bd1bc4213f5e72643c0116450e495b71c7ec128502
root@devstack:/home/sammy# docker inspect --format='{{.State.Status}}' web31 #其状态为 created
created
root@devstack:/home/sammy# docker start web31 #启动容器
web31
root@devstack:/home/sammy# docker inspect --format='{{.State.Status}}' web31 #其状态为 running
running
root@devstack:/home/sammy# docker pause web31 #暂停容器
web31
root@devstack:/home/sammy# docker inspect --format='{{.State.Status}}' web31
paused
root@devstack:/home/sammy# docker unpause web31 #继续容器
web31
root@devstack:/home/sammy# docker inspect --format='{{.State.Status}}' web31
running
root@devstack:/home/sammy# docker rename web31 newweb31 #重命名
root@devstack:/home/sammy# docker inspect --format='{{.State.Status}}' newweb31
running
root@devstack:/home/sammy# docker top newweb31 #在容器中运行 top 命令
UID     PID     PPID    C     STIME    TTY     TIME    CMD
root    5009    4979    0     16:28    ?     00:00:00   python app.py
root@devstack:/home/sammy# docker logs newweb31 #获取容器的日志
 * Running on http://0.0.0.0:5000/ (Press CTRL+C to quit)
root@devstack:/home/sammy# docker stop newweb31 #停止容器
newweb31
root@devstack:/home/sammy# docker inspect --format='{{.State.Status}}' newweb31
exited
root@devstack:/home/sammy# docker rm newweb31 #删除容器
newweb31
root@devstack:/home/sammy# docker inspect --format='{{.State.Status}}' newweb31
Error: No such image, container or task: newweb31

(2) docker stop 和 docker kill

在docker stop 命令执行的时候,会先向容器中PID为1的进程发送系统信号 SIGTERM,然后等待容器中的应用程序终止执行,如果等待时间达到设定的超时时间(默认为 10秒,用户可以指定特定超时时长),会继续发送SIGKILL的系统信号强行kill掉进程。在容器中的应用程序,可以选择忽略和不处理SIGTERM信号,不过一旦达到超时时间,程序就会被系统强行kill掉,因为SIGKILL信号是直接发往系统内核的,应用程序没有机会去处理它。

比如运行 docker stop web5 -t 20 命令后:

2016-09-16T16:01:18.206540853+08:00 container kill b3256ef1400a7f6a6f242e377a77af5e25d3b12237c4ee7c2e9b31a5f6437868 (image=training/webapp, name=web5, signal=15)
2016-09-16T16:01:38.212352224+08:00 container kill b3256ef1400a7f6a6f242e377a77af5e25d3b12237c4ee7c2e9b31a5f6437868 (image=training/webapp, name=web5, signal=9)
2016-09-16T16:01:38.235021315+08:00 container die b3256ef1400a7f6a6f242e377a77af5e25d3b12237c4ee7c2e9b31a5f6437868 (exitCode=137, image=training/webapp, name=web5)

能看到:

  1. 首先 docker 向容器发出 SIGTERM 信号(signal=15)
  2. 等待20秒 (01:18 到 01:38)
  3. 再发送 SIGKILL 系统信号 (signal = 9)
  4. 然后容器被杀掉了 (die)

而 docker kill 命令会直接发出SIGKILL的系统信号,以强行终止容器中程序的运行。运行 docker kill web5 命令后:

2016-09-16T16:06:44.351086471+08:00 container kill b3256ef1400a7f6a6f242e377a77af5e25d3b12237c4ee7c2e9b31a5f6437868 (image=training/webapp, name=web5, signal=9)
2016-09-16T16:06:44.365116100+08:00 container die b3256ef1400a7f6a6f242e377a77af5e25d3b12237c4ee7c2e9b31a5f6437868 (exitCode=137, image=training/webapp, name=web5)
可见直接发出的是 SIGKILL 信号,容器立马就被杀掉了。

(3)使用 docker cp 在 host 和 container 之间拷贝文件或者目录

root@devstack:/home/sammy# docker cp /home/sammy/mydockerbuild/Dockerfile web5:/webapp #从 host 拷贝文件到 container 里面
root@devstack:/home/sammy#
root@devstack:/home/sammy# docker cp web5:/webapp/Dockerfile /home/sammy/Dockerfile #从 container 里面拷贝文件到 host 上
root@devstack:/home/sammy# ls /home/sammy
chroot devstack Dockerfile mongodbdocker mydockerbuild webapp

(4)docker export 和 import

docker export:将一个容器的文件系统打包为一个压缩文件

root@devstack:/home/sammy# docker export web5 -o ./web5
root@devstack:/home/sammy# ls
chroot devstack Dockerfile mongodbdocker mydockerbuild web5 webapp

docker import:从一个压缩文件创建一个镜像

root@devstack:/home/sammy# docker import web5 web5img -m "imported on 0916"
sha256:745bb258be0a69a517367667646148bb2f662565bb3d222b50c0c22e5274a926
root@devstack:/home/sammy# docker history web5img
IMAGE    CREATED    CREATED BY   SIZE    COMMENT
745bb258be0a  6 seconds ago       324 MB    imported on 0916

 2.3 docker run 命令

docker run 命令会创建一个容器并启动它,它也是包含很多的参数,按照用途将它们分类如下:

cgroups 和 namespace 相关:
  --blkio-weight value   Block IO (relative weight), between 10 and 1000
  --blkio-weight-device value Block IO weight (relative device weight) (default [])
  --cgroup-parent string  Optional parent cgroup for the container
  --cpu-percent int    CPU percent (Windows only)
  --cpu-period int    Limit CPU CFS (Completely Fair Scheduler) period
  --cpu-quota int    Limit CPU CFS (Completely Fair Scheduler) quota
 -c, --cpu-shares int    CPU shares (relative weight)
  --cpuset-cpus string   CPUs in which to allow execution (0-3, 0,1)
  --cpuset-mems string   MEMs in which to allow execution (0-3, 0,1)
  --device-read-bps value  Limit read rate (bytes per second) from a device (default [])
  --device-read-iops value  Limit read rate (IO per second) from a device (default [])
  --device-write-bps value  Limit write rate (bytes per second) to a device (default [])
  --device-write-iops value  Limit write rate (IO per second) to a device (default [])
  --ipc string     IPC namespace to use
 -m, --memory string    Memory limit
  --memory-reservation string Memory soft limit
  --memory-swap string   Swap limit equal to memory plus swap: '-1' to enable unlimited swap
  --memory-swappiness int  Tune container memory swappiness (0 to 100) (default -1)
  --kernel-memory string  Kernel memory limit
 -u, --user string     Username or UID (format: <name|uid>[:<group|gid>])
  --userns string    User namespace to use
  --uts string     UTS namespace to use
 -h, --hostname string    Container host name
  --pid string     PID namespace to use
  --pids-limit int    Tune container pids limit (set -1 for unlimited)
  --isolation string   Container isolation technology
  --io-maxbandwidth string  Maximum IO bandwidth limit for the system drive (Windows only)
  --io-maxiops uint    Maximum IOps limit for the system drive (Windows only)
 
 linux process capabilities 相关参数:
  --cap-add value    Add Linux capabilities (default [])
  --cap-drop value    Drop Linux capabilities (default [])
 
 容器运行模式和环境相关:
 -d, --detach      Run container in background and print container ID
 -e, --env value     Set environment variables (default [])
  --env-file value    Read in a file of environment variables (default [])
 
 DNS 相关:
  --dns value     Set custom DNS servers (default [])
  --dns-opt value    Set DNS options (default [])
  --dns-search value   Set custom DNS search domains (default [])
 
 健康检查相关:
  --health-cmd string   Command to run to check health
  --health-interval duration Time between running the check
  --health-retries int   Consecutive failures needed to report unhealthy
  --health-timeout duration  Maximum time to allow one check to run
  --no-healthcheck    Disable any container-specified HEALTHCHECK
  
 IP 和端口:
  --ip string     Container IPv4 address (e.g. 172.30.100.104)
  --ip6 string     Container IPv6 address (e.g. 2001:db8::33)
 -p, --publish value    Publish a container's port(s) to the host (default [])
 -P, --publish-all     Publish all exposed ports to random ports
  --expose value    Expose a port or a range of ports (default [])
  --mac-address string   Container MAC address (e.g. 92:d0:c6:0a:29:33)
  --add-host value    Add a custom host-to-IP mapping (host:ip) (default [])
  
 Volume 相关:
 -v, --volume value    Bind mount a volume (default [])
  --volume-driver string  Optional volume driver for the container
  --volumes-from value   Mount volumes from the specified container(s) (default [])
  --storage-opt value   Storage driver options for the container (default [])
 
 Network 有关:
  --network string    Connect a container to a network (default "default")
  --network-alias value   Add network-scoped alias for the container (default [])
  --link value     Add link to another container (default [])
  --link-local-ip value   Container IPv4/IPv6 link-local addresses (default [])
 
 日志有关:
  --log-driver string   Logging driver for the container
  --log-opt value    Log driver options (default [])
 
 交互性有关:
 -a, --attach value    Attach to STDIN, STDOUT or STDERR (default [])
 -i, --interactive     Keep STDIN open even if not attached
 
 OOM 有关: 
  --oom-kill-disable   Disable OOM Killer
  --oom-score-adj int   Tune host's OOM preferences (-1000 to 1000)
 
 其它(待更进一步分类):
  --cidfile string    Write the container ID to the file
  --detach-keys string   Override the key sequence for detaching a container
  --device value    Add a host device to the container (default [])
  --disable-content-trust  Skip image verification (default true)
  --entrypoint string   Overwrite the default ENTRYPOINT of the image
  --group-add value    Add additional groups to join (default [])
  --help      Print usage
 -l, --label value     Set meta data on a container (default [])
  --label-file value   Read in a line delimited file of labels (default [])
  --name string     Assign a name to the container
  --privileged     Give extended privileges to this container
  --read-only     Mount the container's root filesystem as read only
  --restart string    Restart policy to apply when a container exits (default "no")
  --rm       Automatically remove the container when it exits
  --runtime string    Runtime to use for this container
  --security-opt value   Security Options (default [])
  --shm-size string    Size of /dev/shm, default value is 64MB
  --sig-proxy     Proxy received signals to the process (default true)
  --stop-signal string   Signal to stop a container, SIGTERM by default (default "SIGTERM")
  --sysctl value    Sysctl options (default map[])
  --tmpfs value     Mount a tmpfs directory (default [])
 -t, --tty       Allocate a pseudo-TTY
  --ulimit value    Ulimit options (default [])
 -w, --workdir string    Working directory inside the container

具体的内容以后会有专门文件分析。

3. Doker 平台的基本构成
Docker 平台基本上由三部分组成:

  • 客户端:用户使用 Docker 提供的工具(CLI 以及 API 等)来构建,上传镜像并发布命令来创建和启动容器
  • Docker 主机:从 Docker registry 上下载镜像并启动容器
  • Docker registry:Docker 镜像仓库,用于保存镜像,并提供镜像上传和下载

后面的文章会具体分析。

以上就是本文的全部内容,希望对大家的学习有所帮助,也希望大家多多支持极客世界。


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