Docker教程通俗理解1 -- Docker理解與配置

1. Docker是什麼

    Docker 是一個開源的應用容器引擎，基於 Go 語言 並遵從Apache2.0協議開源。Docker 可以讓開發者打包他們的應用以及依賴包到一個輕量級、可移植的容器中，然後發佈到任何流行的 Linux 機器上，也可以實現虛擬化。容器是完全使用沙箱機制，相互之間不會有任何接口（類似 iPhone 的 app）,容器性能開銷極低。

    特點：像虛擬機但是更加依賴host machine，比之開銷更低，移植性更好

    用Docker的logo來通俗解釋：鯨魚（或者是貨輪）是操作系統，應用程序看作是貨物，原本要將各種各樣形狀、尺寸不同的貨物放到大鯨魚上，你得爲每件貨物考慮怎麼安放（就是應用程序配套的環境），還得考慮貨物和貨物是否能疊起來（應用程序依賴的環境是否會衝突）。現在使用了集裝箱（容器）把每件貨物都放到集裝箱裏，這樣大鯨魚可以用同樣地方式安放、堆疊集裝了，省事省力。

２. Docker的Ubuntu配置

    一個很好的教程 https://www.digitalocean.com/community/tutorials/how-to-install-and-use-docker-on-ubuntu-16-04

需求：64bit Ubuntu + 內核>3.10 (用 uname -r 檢查) + non-root user + sudo 特權

安裝步驟：

        1. add the GPG key for the official Docker repository to the system: 關於gpgkey教程： http://www.ruanyifeng.com/blog/2013/07/gpg.html

 curl -fsSL https://download.docker.com/linux/ubuntu/gpg | sudo apt-key add -

        2.  Add the Docker repository to APT sources list :

sudo add-apt-repository "deb [arch=amd64] https://download.docker.com/linux/ubuntu $(lsb_release -cs) stable"

        3. update the package database with the Docker packages from the newly added repo:

sudo apt-get update

        4. Make sure you are about to install from the Docker repo instead of the default Ubuntu 16.04 repo: 

apt-cache policy docker-ce

        得到類似下圖的輸出

docker-ce:
  Installed: (none)
  Candidate: 17.03.1~ce-0~ubuntu-xenial
  Version table:
     17.03.1~ce-0~ubuntu-xenial 500
        500 https://download.docker.com/linux/ubuntu xenial/stable amd64 Packages
     17.03.0~ce-0~ubuntu-xenial 500
        500 https://download.docker.com/linux/ubuntu xenial/stable amd64 Packages

        5. install 安裝docker社區版本（CE）

sudo apt-get install -y docker-ce

        Docker should now be installed, the daemon started, and the process enabled to start on boot. Check that it's running:
        6. 檢測是否成功運行 查看docker的服務是否啓動

sudo systemctl status docker

        得到類似下圖的輸出

Output
● docker.service - Docker Application Container Engine
   Loaded: loaded (/lib/systemd/system/docker.service; enabled; vendor preset: enabled)
   Active: active (running) since Sun 2016-05-01 06:53:52 CDT; 1 weeks 3 days ago
     Docs: https://docs.docker.com
 Main PID: 749 (docker)
Installing Docker now gives you not just the Docker service (daemon) but also the docker command line utility, or the Docker client. We'll explore how to use the docker command later in this tutorial.   

        如果未啓動服務則使用以下代碼:

$ sudo systemctl enable docker
$ sudo systemctl start docker

        查看是否安裝成功

$ docker run hello-world

3. 避免sudo前綴

     默認情況下， docker 命令會使用 Unix socket 與 Docker 引擎通訊。而只有 root 用戶和docker 組的用戶纔可以訪問 Docker 引擎的 Unix socket。出於安全考慮，一般 Linux 系統上不會直接使用 root 用戶。因此，更好地做法是將需要使用 docker 的用戶加入 docker用戶組。

    0. 創建用戶組(此處爲docker)

    $ sudo groupadd docker

    1. add your username to the docker group:

sudo usermod -aG docker ${USER}

    To apply the new group membership, you can log out of the server and back in, or you can type the following:

su - ${USER}

    You will be prompted to enter your user's password to continue. Afterwards, you can confirm that your user is now added to the docker group by typing:

id -nG

Output
sammy sudo docker
    If you need to add a user to the docker group that you're not logged in as, declare that username explicitly using:

sudo usermod -aG docker username

    The rest of this article assumes you are running the docker command as a user in the docker user group. If you choose not to, please prepend the commands with sudo.

4. Docker的命令行

    1. docker查看所有指令

docker
As of Docker 1.11.1, the complete list of available subcommands includes:


Output


    attach    Attach to a running container
    build     Build an image from a Dockerfile
    commit    Create a new image from a container's changes
    cp        Copy files/folders between a container and the local filesystem
    create    Create a new container
    diff      Inspect changes on a container's filesystem
    events    Get real time events from the server
    exec      Run a command in a running container
    export    Export a container's filesystem as a tar archive
    history   Show the history of an image
    images    List images
    import    Import the contents from a tarball to create a filesystem image
    info      Display system-wide information
    inspect   Return low-level information on a container or image
    kill      Kill a running container
    load      Load an image from a tar archive or STDIN
    login     Log in to a Docker registry
    logout    Log out from a Docker registry
    logs      Fetch the logs of a container
    network   Manage Docker networks
    pause     Pause all processes within a container
    port      List port mappings or a specific mapping for the CONTAINER
    ps        List containers
    pull      Pull an image or a repository from a registry
    push      Push an image or a repository to a registry
    rename    Rename a container
    restart   Restart a container
    rm        Remove one or more containers
    rmi       Remove one or more images
    run       Run a command in a new container
    save      Save one or more images to a tar archive
    search    Search the Docker Hub for images
    start     Start one or more stopped containers
    stats     Display a live stream of container(s) resource usage statistics
    stop      Stop a running container
    tag       Tag an image into a repository
    top       Display the running processes of a container
    unpause   Unpause all processes within a container
    update    Update configuration of one or more containers
    version   Show the Docker version information
    volume    Manage Docker volumes
    wait      Block until a container stops, then print its exit code

0. 其他問題:

    a. 使用docker出現timeout錯誤

Unable to find image 'hello-world:latest' locally
latest: Pulling from library/hello-world
78445dd45222: Pulling fs layer
docker: error pulling image configuration: Get https://dseasb33srnrn.cloudfront.net/registry-v2/docker/registry/v2/blobs/sha256/48/48b5124b2768d2b917edcb640435044a97967015485e812545546cbed5cf0233/data?Expires=1490975964&Signature=OUmibCvoXIlDlmt-GF187GDtJySfLIHJdgfs~GTyzARgOPaVYLfU8kLKKFnS3NczD39-PtCdTxEMKmE0IigxpsmDQimidTyuqOIlac-wDGhrLPveHoKIUYZ9QP9hzzAvRyhci9wrsWJJkrsOz3ITUaNRDM3z9xHyyQi07WQGLiQ_&Key-Pair-Id=APKAJECH5M7VWIS5YZ6Q: dial tcp: lookup dseasb33srnrn.cloudfront.net on 192.168.65.1:53: read udp 192.168.65.2:55172->192.168.65.1:53: i/o timeout.
See 'docker run --help'.

    Solu: may be you are behind a firewall/proxy server. i was also behind my office firewall so i tried below steps which resolved this issue.

    For setting up proxy for docker, please do the following:
    (1). Create a systemd drop-in directory for the docker service:

        $ mkdir -p /etc/systemd/system/docker.service.d
        $ vim /etc/systemd/system/docker.service.d/http-proxy.conf

        Then add below content with proxy settings with it，注意將addr和port換成代理的host和port

        [Service]
        Environment="HTTP_PROXY=http://<allowed_proxy_ipv4_address>:<proxy_port_num>/"   

    (2). For HTTPS proxy server:

        $ vim /etc/systemd/system/docker.service.d/https-proxy.conf

        Then add below content with proxy settings with it

        [Service]
        Environment="HTTPS_PROXY=https://<allowed_proxy_ipv4_address>:<proxy_port_num>/"

    (3). Flush changes execute: $ sudo systemctl daemon-reload
    (4). Restart Docker: $ sudo systemctl restart docker

    (5). Verify that the configuration has been loaded: $ systemctl show --property=Environment docker