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Docker Lab: Linking Frontend and Backend

Previously in the lab...

Question: Can I somehow link the containers together so they can talk to each other?

Answer: Yes, you can! And here's how it works.

Linking Containers

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

$ docker container ls
CONTAINER ID        IMAGE               COMMAND                  CREATED             STATUS              PORTS                NAMES
6b0721fa6103        php:7-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

Sadly before we can link the frontend and backend we have to get rid of the existing containers.

$ 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 the communication between two or more Docker containers you have to use Docker network. Per default there are three networks available:

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

For this exercise we are creating our own network with docker network create docker-techlab. If you now rerun the list command for Docker networks you should see the newly created network.

To make the backend accessable/visible to the frontend (via Container-NAMES) you have to run both containers with the --network option:

$ docker run -d --network docker-techlab --name apache-php -v /home/[path]/php-app:/var/www/html -p8080:80 php:7-apache
$ docker run -d --network docker-techlab --name mariadb-container-with-existing-external-volume -v volume-mariadb:/var/lib/mysql -e MYSQL_ROOT_PASSWORD=my-secret-pw mariadb

If you now access the containers you should be able to resolve the other's container address with its container name.

$ docker exec -it mariadb-container-with-existing-external-volume bash
root@6f08ac657320:/# getent hosts apache-php

Now the two containers can talk to each other. Let's check this:

If you now type http://localhost:8080/db.php in your browser you should get... an error! Because the mysqli extension is not found.

Question: I don't want to go to the Docker instance and install every missing extension manually. Is there a way to solve this problem?

I'm sure there is, let's check out the next lab to find out how.

← Embedding the Source Code | Building Your Own Docker Image →