docker中 镜像 容器区别 关系

来源:互联网 发布:芜湖淘宝招聘网 编辑:程序博客网 时间:2024/04/29 21:02

参考文章:https://segmentfault.com/q/1010000004611666 感谢作者分享

镜像是文件, 容器是进程。 容器是基于镜像创建的, 即容器中的进程依赖于镜像中的文件, 这里的文件包括进程运行所需要的可执行文件, 依赖软件, 库文件, 配置文件等等...

不妨通过一个实例来获得更直观的认识。假设你需要把nginx(web服务器)运行在Docker容器中, 则第一步需要下载nginx镜像:

sudo docker pull nginx

下载nginx镜像之后可以查看Docker镜像:

sudo docker imagesREPOSITORY          TAG                 IMAGE ID            CREATED             SIZEnginx               latest              0d409d33b27e        2 weeks ago         182.7 MB

  • 可知, nginx镜像的大小为182.7MB。

  • 事实上, nginx镜像并非一个单独的文件,而是具有层级结构

sudo docker history nginxIMAGE               CREATED             CREATED BY                                      SIZE                COMMENT0d409d33b27e        2 weeks ago         /bin/sh -c #(nop) CMD ["nginx" "-g" "daemon o   0 B                 <missing>           2 weeks ago         /bin/sh -c #(nop) EXPOSE 443/tcp 80/tcp         0 B                 <missing>           2 weeks ago         /bin/sh -c ln -sf /dev/stdout /var/log/nginx/   0 B                 <missing>           2 weeks ago         /bin/sh -c apt-key adv --keyserver hkp://pgp.   57.67 MB            <missing>           2 weeks ago         /bin/sh -c #(nop) ENV NGINX_VERSION=1.11.1-1~   0 B                 <missing>           3 weeks ago         /bin/sh -c #(nop) MAINTAINER NGINX Docker Mai   0 B                 <missing>           3 weeks ago         /bin/sh -c #(nop) CMD ["/bin/bash"]             0 B                 <missing>           3 weeks ago         /bin/sh -c #(nop) ADD file:5d8521419ad6cfb695   125.1 MB 
可知, nginix镜像一共有8层, 其中, 第1层为125.1MB, 第5层为57.67MB, 其他层的大小可以忽略。
将nginx运行在Docker容器中:
sudo docker run -itd \                -p 80:80 \                --name=nginx \                nginx 
查看nginx容器
sudo docker psCONTAINER ID        IMAGE               COMMAND                  CREATED             STATUS              PORTS                         NAMES263e88fc53d3        nginx               "nginx -g 'daemon off"   3 seconds ago       Up 2 seconds        0.0.0.0:80->80/tcp, 443/tcp   nginx
可知, nginx容器运行成功。

查看nginx容器中的进程

sudo docker exec nginx ps aux | grep -v psUSER       PID %CPU %MEM    VSZ   RSS TTY      STAT START   TIME COMMANDroot         1  0.0  0.0  31680  2872 ?        Ss+  05:18   0:00 nginx: master process nginx -g daemon off;nginx        5  0.0  0.0  32072  1696 ?        S+   05:18   0:00 nginx: worker process


可知, nginx容器中一共运行了两个进程, 分别是nginx的master和worker进程。
容器中进程的COMMAND为"nginx -g daemon off", 但是, 主机上并未安装nginx, nginx安装在Docker镜像中。

不妨再次查看nginx镜像的各个层,这时使用"--no-trunc"显示详细内容:

docker history --no-trunc nginxIMAGE                                                                     CREATED             CREATED BY                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   SIZE                COMMENTsha256:0d409d33b27e47423b049f7f863faa08655a8c901749c2b25b93ca67d01a470d   2 weeks ago         /bin/sh -c #(nop) CMD ["nginx" "-g" "daemon off;"]                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           0 B                 <missing>                                                                 2 weeks ago         /bin/sh -c #(nop) EXPOSE 443/tcp 80/tcp                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      0 B                 <missing>                                                                 2 weeks ago         /bin/sh -c ln -sf /dev/stdout /var/log/nginx/access.log  && ln -sf /dev/stderr /var/log/nginx/error.log                                                                                                                                                                                                                                                                                                                                                                                                                                      0 B                 <missing>                                                                 2 weeks ago         /bin/sh -c apt-key adv --keyserver hkp://pgp.mit.edu:80 --recv-keys 573BFD6B3D8FBC641079A6ABABF5BD827BD9BF62  && echo "deb http://nginx.org/packages/mainline/debian/ jessie nginx" >> /etc/apt/sources.list  && apt-get update  && apt-get install --no-install-recommends --no-install-suggests -y       ca-certificates       nginx=${NGINX_VERSION}       nginx-module-xslt       nginx-module-geoip       nginx-module-image-filter       nginx-module-perl       nginx-module-njs       gettext-base  && rm -rf /var/lib/apt/lists/*   57.67 MB            <missing>                                                                 2 weeks ago         /bin/sh -c #(nop) ENV NGINX_VERSION=1.11.1-1~jessie                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          0 B                 <missing>                                                                 3 weeks ago         /bin/sh -c #(nop) MAINTAINER NGINX Docker Maintainers "docker-maint@nginx.com"                                                                                                                                                                                                                                                                                                                                                                                                                                                               0 B                 <missing>                                                                 3 weeks ago         /bin/sh -c #(nop) CMD ["/bin/bash"]                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          0 B                 <missing>                                                                 3 weeks ago         /bin/sh -c #(nop) ADD file:5d8521419ad6cfb6956ed26ab70a44422d512f82462046ba8e68b7dcb8283f7e in /                                                                                                                                                                                                                                                                                                                                                                                                                                             125.1 MB  

其中, 第5层为57.67MB, 它的CREATED BY是这样的(把连接符号&&换为换行符):

apt-key adv --keyserver hkp://pgp.mit.edu:80 --recv-keys 573BFD6B3D8FBC641079A6ABABF5BD827BD9BF62  echo "deb http://nginx.org/packages/mainline/debian/ jessie nginx" >> /etc/apt/sources.list  apt-get updateapt-get install --no-install-recommends --no-install-suggests -y ca-certificates nginx=${NGINX_VERSION} nginx-module-xslt nginx-module-geoip nginx-module-image-filter nginx-module-perl nginx-module-njs gettext-baserm -rf /var/lib/apt/lists/*


可知, nginx镜像的第5层安装了nginx