Linking Containers in Docker

Tested Infrastructure

Platform	Number of Instance	Reading Time
Mac OS	1	5 min

Pre-requisite

A linux system (here we have used macbook)
Docker installed

In order to connect together multiple docker containers or services running inside docker container, ‘–link’ flag can be used in order to securely connect and provide a channel to transfer information from one container to another. A simple application of using a Wordpress container linked to MySQL container, can explain this well

Pull the latest MySql container

$ docker pull mysql:latest
latest: Pulling from library/mysql
a5a6f2f73cd8: Already exists
936836019e67: Pull complete
283fa4c95fb4: Pull complete
1f212fb371f9: Pull complete
e2ae0d063e89: Pull complete
5ed0ae805b65: Pull complete
0283dc49ef4e: Pull complete
a7e1170b4fdb: Pull complete
88918a9e4742: Pull complete
241282fa67c2: Pull complete
b0fecf619210: Pull complete
bebf9f901dcc: Pull complete
Digest: sha256:b7f7479f0a2e7a3f4ce008329572f3497075dc000d8b89bac3134b0fb0288de8
Status: Downloaded newer image for mysql:latest

Run MySql Container in detach mode (MySQL 8 changed the password authentication method. We’re looking for the mysql_native_password plugin, hence “–default-authentication-plugin=mysql_native_password” option require)

$ docker run --name mysql01 -e MYSQL_ROOT_PASSWORD=Password1234 -d mysql --default-authentication-plugin=mysql_native_password
fdabd410a66e4b65ec959677c932ccad79542ee9081d86ad2cbd0e2fe0265f1d

Pull Wordpress docker container

$ docker pull wordpress:latest
latest: Pulling from library/wordpress
a5a6f2f73cd8: Already exists
633e0d1cd2a3: Pull complete
fcdfdf7118ba: Pull complete
4e7dc76b1769: Pull complete
c425447c8835: Pull complete
75780b7b9977: Pull complete
33ed51bc30e8: Pull complete
7c4215700bc4: Pull complete
d4f613c1e621: Pull complete
de5465a3fde0: Pull complete
6d373ffaf200: Pull complete
991bff14f001: Pull complete
d0a8c1ecf326: Pull complete
aa3627a535bb: Pull complete
a36be75bb622: Pull complete
98ebddb8e6ca: Pull complete
ed6e19b74de1: Pull complete
18b9cc4a2286: Pull complete
dfe625c958ac: Pull complete
Digest: sha256:f431a0681072aff336acf7a3736a85266fe7b46de116f29a2ea767ff55ad8f54
Status: Downloaded newer image for wordpress:latest

Run the wordpress container linking it to MySQL Container (will run the database container with name “mysql-wordpress” and will set root password for MySQL container)

$ docker run --name wordpress01 --link mysql01 -p 8080:80 -e WORDPRESS_DB_HOST=mysql01:3306 -e WORDPRESS_DB_USER=root -e WORDPRESS_DB_PASSWORD=Password1234 -e WORDPRESS_DB_NAME=wordpress -e WORDPRESS_TABLE_PREFIX=wp_ -d wordpress
83b1f3215b01e7640246eb945977052bbf64f500a5b7fa18bd5a27841b01289b

Check the status of the Containers

$ docker ps
CONTAINER ID        IMAGE               COMMAND                  CREATED              STATUS              PORTS                  NAMES
83b1f3215b01        wordpress           "docker-entrypoint.s…"   33 seconds ago       Up 32 seconds       0.0.0.0:8080->80/tcp   wordpress01
fdabd410a66e        mysql               "docker-entrypoint.s…"   About a minute ago   Up About a minute   3306/tcp, 33060/tcp    mysql01

As, we have linked both the container now wordpress container can be accessed from browser using the address http://localhost:8080 and setup of wordpress can be done easily.

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