9. Linking frontend and backend

Now it is time to link your frontend and backend together.

Linking containers

If you have properly worked through all the previous labs you now have the following setup:

docker ps

CONTAINER ID        IMAGE               COMMAND                  CREATED             STATUS              PORTS                NAMES
6b0721fa6103        php:8-apache        "docker-php-entryp..."   25 minutes ago      Up 25 minutes       0.0.0.0:8080->80/tcp   apache-php
50197361e87b        mariadb             "docker-entrypoint..."   2 hours ago         Up 2 hours          3306/tcp             mariadb-container-with-existing-external-volume
6f08ac657320        mariadb             "docker-entrypoint..."   5 hours ago         Up 3 hours          3306/tcp             mariadb-container

We will put the containers into a new, dedicated network. But first get rid of the currently running ones:

docker stop apache-php mariadb-container mariadb-container-with-existing-external-volume
docker rm apache-php mariadb-container mariadb-container-with-existing-external-volume

To enable communication between containers, use docker network. By default, Docker provides three networks. Verify this is the case:

docker network ls

Will output the following:

NETWORK ID          NAME                DRIVER              SCOPE
9233283df4a6        bridge              bridge              local
640877f8aec4        host                host                local
72f9a9996909        none                null                local

For this exercise create a new network with:

docker network create container-basics-training

If you rerun the list command for Docker networks now, container-basics-training will show up.

To make the backend accessible from the frontend run both containers with the --network option:

Linux/Webshell:

docker run -d --network container-basics-training --name apache-php -v $(pwd)/php-app:/var/www/html -p 8080:80 php:8-apache
docker run -d --network container-basics-training --name mariadb-container-with-existing-external-volume -v volume-mariadb:/var/lib/mysql -e MARIADB_ROOT_PASSWORD=my-secret-pw mariadb

Windows (Git Bash):

MSYS_NO_PATHCONV=1 docker run -d --network container-basics-training --name apache-php -v $(pwd)/php-app:/var/www/html -p 8080:80 php:8-apache
docker run -d --network container-basics-training --name mariadb-container-with-existing-external-volume -v volume-mariadb:/var/lib/mysql -e MARIADB_ROOT_PASSWORD=my-secret-pw mariadb

If you access either container, you should be able to resolve the other container’s address with its container name.

Execute an interactive bash shell on the mariadb container.

docker exec -it mariadb-container-with-existing-external-volume bash

You are now in the Bash session of the mariadb container and the prompt will look like root@6f08ac657320:/#

Get the address of the apache-php container.

getent hosts apache-php

The two containers are now able to talk to each other. But let’s check this:

If you type http://localhost:8080/db.php in your browser or use curl http://localhost:8080/db.php in the webshell you get… an error! This is because the mysqli extension is not installed in the container.

Obviously, we will not install it in the running container but build a new image. More on that in the next lab.