In our last post, we installed a variety of prerequisites to let us run a multi-container
application using docker-compose. In this post, we will get started with a WordPress
instance. The working directory for this step will be docker-lamp/wordpress1. Looking
in the directory, we see two files: docker-compose.yml and README.md (which contains this
text). Our docker-compose.yml is quite simple at this stage:
version: "3"
services:
wordpress:
restart: always
image: wordpress:6.1-apache
environment:
WORDPRESS_DB_HOST: 'db'
WORDPRESS_DB_USER: 'wordpress'
WORDPRESS_DB_PASSWORD: 'password1234'
WORDPRESS_DB_NAME: 'wordpress'
ports:
- 80:80
networks:
- external_network
volumes:
- ./wordpress:/var/www/html
db:
image: mysql/mysql-server:8.0
restart: always
environment:
MYSQL_DATABASE: 'wordpress'
MYSQL_USER: 'wordpress'
MYSQL_PASSWORD: 'password1234'
MYSQL_ROOT_PASSWORD: 'password'
healthcheck:
test: "mysql $$MYSQL_DATABASE -u$$MYSQL_USER -p$$MYSQL_PASSWORD -e 'SELECT 1;'"
interval: 20s
timeout: 10s
retries: 5
networks:
- external_network
volumes:
- ./mysql/wordpress:/var/lib/mysql
- ./mysql/logs:/var/log/mysql
- ./mysql/initdb:/docker-entrypoint-initdb.d
networks:
external_network:
We are going to download and start two containers, mysql/mysql-server and wordpress.
Each of these containers have multiple options – for WordPress we will download version
6.1 configured to use Apache 2, and for MySQL, we download the mysql-server version 8.0
container. Both of these containers support configuration through environment variables
which is documented on their respective pages on DockerHub
(mysql-server,
wordpress) –
the environment variables we pass into the MySQL database will auto-create the
wordpress database, and create a wordpress user with the password password1234 –
and while, in principle, the database is not accessible to the outside world, you should
probably choose a different password ;-)
One interesting feature of this first configuration file is the healthcheck section
for MySQL. As we advance in the project, it can take a few seconds before MySQL is ready
to accept connections. We add a healthcheck which runs a trivial query. It waits 20s
between checks, and in a future step, we will delay starting the wordpress containers
until the database is finished its initialization.
Inside our project, the containers will be able to talk to each other using just their
service name. That’s why, in our WordPress container, we can set the WORDPRESS_DB_HOST
environment variable to just db. As we will see when we start our application, the
containers will be started with the name $PROJECT-$SERVICE-$VERSION – the project
name is taken from the directory, and the service names are wordpress for our
WordPress container, and db for our MySQL database. If we want to refer to a
container by name from the host, we will have to use the full name wordpress1-db-1
or wordpress1-wordpress-1.
We also add all containers to a Docker bridge network we create just for our application,
called external-network and we connect port 80 of our WordPress container to port 80
of our host, so that connections to http://$IP_ADDRESS:80 are handled by the container.
To enable our data to persist after the containers are deleted, we also use some local
volumes to map some local directories in our project to locations “mounted” in our
containers. Importantly, we will create our database in the directory mysql/wordpress
and will put the WordPress installation files (which will include things like uploaded
files and plug-ins) in wordpress.
To ensure that everything works correctly, we will create the directories before we get started:
mkdir -p mysql/initdb mysql/logs mysql/wordpress
docker-compose up -d
If everything has gone well, you should see Docker pulling two containers consisting of
about 30 “layers”, creating our network, and starting the containers. We can verify that the
containers started correctly with docker-compose ps and if you now go to http://$IP_ADDRESS
(obtained from your OCI console) you should see the WordPress installation screen.
[opc@cloud-native-wordpress wordpress1]$ docker-compose ps
NAME IMAGE COMMAND SERVICE CREATED STATUS PORTS
wordpress1-db-1 mysql/mysql-server:8.0 "/entrypoint.sh mysq…" db 3 hours ago Up 3 hours (healthy) 3306/tcp, 33060-33061/tcp
wordpress1-wordpress-1 wordpress:6.1-apache "docker-entrypoint.s…" wordpress 3 hours ago Up 3 hours 0.0.0.0:80->80/tcp, :::80->80/tcp
Clicking through this, we can now name our blog, create a user ID and password, and log in to our blog to see a “Hello World” post, create our first page, and write our first blog entry – all running in containers, and started in a few minutes!
In our next step, we will augment this application by moving to an nginx proxy, and
pre-loading some content into our blog. You can now bring down your WordPress instance
with docker-compose down and move on to step 2.