Master Building Docker WordPress Images and Understanding ENTRYPOINT vs CMD

Docker Practical Preparation

Four steps: log in to OSChina Git, fork the docker‑training repository, connect to the server via SSH, and clone the repository.

Build csphere/wordpress:4.2 Image

# cd docker-training/wordpress/
# ls -a
.              license.txt           wp-config-sample.php  wp-login.php
..             readme.html           wp-content            wp-mail.php
Dockerfile     wp-activate.php       wp-cron.php           wp-settings.php
.dockerignore  wp-admin              wp-includes           wp-signup.php
index.php      wp-blog-header.php    wp-links-opml.php     wp-trackback.php
init.sh        wp-comments-post.php  wp-load.php           xmlrpc.php

# cat Dockerfile 
from csphere/php-fpm:5.4

add init.sh /init.sh

entrypoint ["/init.sh", "/usr/bin/supervisord", "-n", "-c", "/etc/supervisord.conf"]

Use a .dockerignore file to exclude files that should not be packaged.

Base image is csphere/php-fpm:5.4.

The ONBUILD instruction copies the code into the web root. init.sh configures the WordPress MySQL connection, so the database is ready when the container starts.

Build the image: docker build -t csphere/wordpress:4.2 . List local images: docker images Find the host IP address: ifconfig eth0 Run the WordPress container:

docker run -d -p 80:80 --name wordpress -e WORDPRESS_DB_HOST=192.168.1.20 -e WORDPRESS_DB_USER=admin -e WORDPRESS_DB_PASSWORD=csphere2015 csphere/wordpress:4.2

-d

runs the container in the background. -p 80:80 maps host port 80 to container port 80. --name wordpress names the container. -e WORDPRESS_DB_HOST=192.168.1.20 sets the database host IP. -e WORDPRESS_DB_USER=admin sets the database user. -e WORDPRESS_DB_PASSWORD=csphere2015 sets the database password.

The image csphere/wordpress:4.2 creates the container.

Access http://your_ip, choose a language, and complete the WordPress setup.

ENTRYPOINT vs CMD

ENTRYPOINT configures a container to run as an executable. Preferred exec form: ENTRYPOINT ["executable", "param1", "param2"] Shell form: ENTRYPOINT command param1 param2 CMD provides default parameters to ENTRYPOINT or runs a command. Preferred exec form: CMD ["executable", "param1", "param2"] It can also supply parameters to ENTRYPOINT: CMD ["param1", "param2"] Or use the shell form:

CMD command param1 param2

Practical test of CMD

vim Dockerfile
FROM centos:centos7.1.1503

CMD ["/bin/echo", "This is test cmd"]

docker build -t csphere/cmd:0.1 .

docker run -it --rm csphere/cmd:0.1
# Output: This is test cmd

Providing a new command at docker run overrides the CMD:

docker run -it csphere/cmd:0.1 /bin/bash
# You get a shell

Practical test of ENTRYPOINT

FROM centos:centos7.1.1503

ENTRYPOINT ["/bin/echo", "This is test entrypoint"]

docker build -t csphere/ent:0.1 .

docker run -it csphere/ent:0.1
# Output: This is test entrypoint

By default, ENTRYPOINT cannot be overridden, but it can be replaced using the --entrypoint option:

docker run -it --entrypoint=/bin/bash csphere/ent:0.1
# You get a shell

This demonstrates that ENTRYPOINT is fixed unless explicitly changed at run time, while CMD is more flexible.