Docker安装

$ sudo yum install -y yum-utils \
  device-mapper-persistent-data \
  lvm2
$ sudo yum-config-manager \
    --add-repo \
    https://download.docker.com/linux/centos/docker-ce.repo
$ sudo yum install docker-ce
$ sudo systemctl start docker
$ sudo systemctl enable docker

设置国内镜像仓库地址

$ sudo dockerd --registry-mirror=https://registry.docker-cn.com

拉取CentOS镜像

$ sudo docker pull centos

编写Dockerfile支持systemd基础镜像

FROM centos:7
ENV container docker
RUN (cd /lib/systemd/system/sysinit.target.wants/; for i in *; do [ $i == \
systemd-tmpfiles-setup.service ] || rm -f $i; done); \
rm -f /lib/systemd/system/multi-user.target.wants/*;\
rm -f /etc/systemd/system/*.wants/*;\
rm -f /lib/systemd/system/local-fs.target.wants/*; \
rm -f /lib/systemd/system/sockets.target.wants/*udev*; \
rm -f /lib/systemd/system/sockets.target.wants/*initctl*; \
rm -f /lib/systemd/system/basic.target.wants/*;\
rm -f /lib/systemd/system/anaconda.target.wants/*;
VOLUME [ "/sys/fs/cgroup" ]
CMD ["/usr/sbin/init"]

构建支持systemd基础镜像

$ sudo docker build --rm -t local/c7-systemd .

基于基础镜像编写httpd服务镜像

FROM local/c7-systemd
RUN yum -y install httpd; yum clean all; systemctl enable httpd.service
EXPOSE 80
CMD ["/usr/sbin/init"]

构建httpd服务镜像

$ sudo docker build --rm -t local/c7-systemd-httpd .

运行httpd服务镜像

$ sudo docker run -tid --privileged=true \
  -v /sys/fs/cgroup:/sys/fs/cgroup:ro -p 80:80 \
  local/c7-systemd-httpd

注意：–privileged=true参数，表示容器拥有root权限，官方文档没有加这个参数，我测试时镜像启动出错。

在容器中查看systemctl命令

$ sudo docker exec -it <your-container-name> bash
$ sudo systemctl status httpd

完美看到httpd运行情况：

● httpd.service - The Apache HTTP Server
   Loaded: loaded (/usr/lib/systemd/system/httpd.service; enabled; vendor preset: disabled)
   Active: active (running) since Thu 2018-09-06 08:02:56 UTC; 2min 11s ago
     Docs: man:httpd(8)
           man:apachectl(8)
 Main PID: 18 (httpd)
   Status: "Total requests: 10; Current requests/sec: 0; Current traffic:   0 B/sec"
   CGroup: /docker/7ded642bc79721ca7013a8b337b8e049ec83afe8ea9fe9b73ce40866fd8064a2/system.slice/httpd.service
           ├─18 /usr/sbin/httpd -DFOREGROUND
           ├─20 /usr/sbin/httpd -DFOREGROUND
           ├─21 /usr/sbin/httpd -DFOREGROUND
           ├─22 /usr/sbin/httpd -DFOREGROUND
           ├─23 /usr/sbin/httpd -DFOREGROUND
           ├─24 /usr/sbin/httpd -DFOREGROUND
           ├─25 /usr/sbin/httpd -DFOREGROUND
           ├─26 /usr/sbin/httpd -DFOREGROUND
           └─27 /usr/sbin/httpd -DFOREGROUND

Sep 06 08:02:56 7ded642bc797 systemd[1]: Starting The Apache HTTP Server...
Sep 06 08:02:56 7ded642bc797 httpd[18]: AH00558: httpd: Could not reliably determine the server's fully qua...ssage
Sep 06 08:02:56 7ded642bc797 systemd[1]: Started The Apache HTTP Server.
Hint: Some lines were ellipsized, use -l to show in full.

参考资料

[1] Docker安装指南: https://docs.docker.com/install/linux/docker-ce/centos/
[2] Docker Hub CentOS: https://hub.docker.com/_/centos/
[3] Docker国内镜像设置指南: https://docs.docker.com/registry/recipes/mirror/#use-case-the-china-registry-mirror