Mastering Docker Compose: Networks, Volumes, and Container Communication

Table of contents

• Table of Contents

• 1. Introduction

• 2. What is Docker Compose?

• 3. Setup and Prerequisites

• 4. Building a Docker Compose File

• 5. Starting the Containers

• 6. Testing Container-to-Container Communication

• 7. Understanding Volumes (Shared Data Between Containers)

• 8. Accessing Shared Files from the Host Machine

• 9. Stop and Remove Containers

• 10. Summary

• 11. Docker Compose Cleanup Summary

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Table of Contents

1. Introduction

2. What is Docker Compose?

3. Setup and Prerequisites

4. Building a Docker Compose File

5. Starting the Containers

6. Testing Container -to- Container Communication

7. Understanding Volumes (Shared Data Between Containers)

8. Accessing Shared Files from the Host Machine

9. Stop and Remove Containers

10. Summary and Real-World Use Case

11. Docker Compose Cleanup Summary

1. Introduction

Docker Compose is one of the most powerful tools in the DevOps world — it helps you define, manage, and run multi-container applications effortlessly.

In this blog, we’ll walk through a real example where:

• We connect two containers: Nginx and MySQL

• Share data between them using volumes

• Enable communication between containers through networks

• Access that shared data from both inside and outside Docker!

By the end, you’ll have a solid understanding of how to build a production-style setup using docker-compose.

2. What is Docker Compose?

Docker Compose allows you to define and run multiple containers using a single file — docker-compose.yml.
Instead of running many docker run commands, you just define everything in YAML format and start all containers together.

3. Setup and Prerequisites

Make sure you have Docker and Docker Compose installed.

sudo apt update
sudo apt install docker.io -y
sudo apt install docker-compose -y

Check the versions:

docker --version
docker compose version

Create a working directory:

mkdir ~/compose && cd ~/compose

4. Building a Docker Compose File

Let’s create a file named docker-compose.yml:

vim docker-compose.yml

Paste this content 👇

services:

  nginx:
    image: nginx:latest
    container_name: nginx
    ports:
      - 80:80
    volumes:
      - shared-data:/shared
    networks:
      - docker-network

  mysql:
    image: mysql:latest
    container_name: mysql
    environment:
      MYSQL_ROOT_PASSWORD: root
      MYSQL_DATABASE: my_db
      MYSQL_USER: myuser
      MYSQL_PASSWORD: user
    volumes:
      - shared-data:/shared
    networks:
      - docker-network

volumes:
  shared-data:

networks:
  docker-network:

5. Starting the Containers

Now, run the following command:

docker compose up -d

Check if containers are running:

docker ps

6. Testing Container-to-Container Communication

You can test network connectivity using ping.

First, install ping inside Nginx container:

docker exec -it nginx bash
apt update && apt install -y iputils-ping   #iputils-ping is the package that contains the ping command

Then test:

ping mysql

Expected output:

PING mysql (172.18.0.3) 56(84) bytes of data.
64 bytes from mysql.compose_docker-network (172.18.0.3): icmp_seq=1 ttl=64 time=0.04 ms

This means Nginx successfully communicates with MySQL via Docker network.

7. Understanding Volumes (Shared Data Between Containers)

Both containers share the same volume named shared-data.
That means — if you create a file inside /shared in one container,
you can read it from the other!

Enter inside the Nginx container:

docker exec -it nginx bash

Create a file:

echo "Hello from Nginx!" > /shared/test.txt    # Create a File {test.txt} inside shared Folder
cat /shared/test.txt
Hello from Nginx!
Exit                           #Exit from nginx Container

Now go inside MySQL container:

docker exec -it mysql bash           #Enter inside mysql container

Read the same file:

cat /shared/test.txt                 #See the mess

You’ll see:

Hello from Nginx!

This confirms both containers share the same data.

8. Accessing Shared Files from the Host Machine

Docker stores named volumes on the host system under:

Docker volume inspect compose_shared-data       #See docker volume mountpoint path

"Mountpoint": "/var/lib/docker/volumes/compose_shared-data/_data",

Let’s locate our shared-data volume:

cd /var/lib/docker/volumes/compose_shared-data/_data 
ls
cat test.txt

You’ll see the same file and message:

hello from docker

That means — the same data is now visible:

• Inside Nginx

• Inside MySQL

• And on your Ubuntu host

9. Stop and Remove Containers

If you want to stop everything:

docker compose down

This removes containers and networks but keeps the volume (data safe).

If you want to remove volumes too:

docker compose down -v

10. Summary

You learned how to:

• Create and use Docker networks

• Create and share volumes between containers

• Connect containers and test communication

• Access data from both containers and host

11. Docker Compose Cleanup Summary

When you’re done experimenting with your containers, you’ll often need to clean things up.
Here’s what each docker compose down option does 👇

Command	What It Removes	Images Deleted?
docker compose down	Stops and removes containers and networks created by Compose	❌ No
docker compose down --volumes	Removes containers, networks, and volumes	❌ No
docker compose down --rmi local	Removes everything above plus locally built images (from build: in Compose)	⚠️ Yes (only built images)
docker compose down --rmi all	Removes containers, networks, volumes, and all images	✅ Yes (all images)