关于 docker-compose 问题

• 今天刚学习 docker-compose，我使用 docker-compose+Dockerfile。只创建了容器了，没有运行容器，直接退出了，不知道是什么原因。
• 下面是配置文件和启动命令

[root@localhost compose]# cat docker-compose.yml 
version: '3'
services:
  web:
    build: .
    ports:
      - "8888:80"
[root@localhost compose]# cat Dockerfile 
FROM centos:7
MAINTAINER xy
RUN yum install -y httpd php php-gd php-mysql;systemctl enable httpd.service
RUN echo "<?php phpinfo()?>" > /var/www/html/index.php
EXPOSE 80

[root@localhost compose]# docker-compose up
 ---> d45344adbd48
Step 6/6 : EXPOSE 80
 ---> Running in 8ba263e41682
Removing intermediate container 8ba263e41682
 ---> b826f2af0a7c
Successfully built b826f2af0a7c
Successfully tagged compose_web:latest
WARNING: Image for service web was built because it did not already exist. To rebuild this image you must use `docker-compose build` or `docker-compose up --build`.
Creating compose_web_1 ... 
Creating compose_web_1 ... done
Attaching to compose_web_1
compose_web_1 exited with code 0

[root@localhost compose]# docker ps
CONTAINER ID        IMAGE               COMMAND             CREATED             STATUS              PORTS               NAMES

[root@localhost compose]# docker ps -a
CONTAINER ID        IMAGE               COMMAND                  CREATED             STATUS                      PORTS               NAMES
69675d705d29        compose_web         "/bin/bash"              14 seconds ago      Exited (0) 14 seconds ago                       compose_web_1
54794397b730        6d53ff0be550        "/bin/sh -c 'yum ins …"   2 hours ago         Exited (1) 2 hours ago    

[root@localhost compose]# docker-compose ps
    Name         Command    State    Ports 
------------------------------------------
compose_web_1   /bin/bash   Exit 0