How to Mount a Host Directory as a Volume in Docker Compose

Mounting a host directory as a volume in Docker Compose allows you to share data between the host machine and a container. This is useful for persisting data, sharing configuration files, or enabling live code reloading during development. In this guide, we will explore two methods for mounting a host directory as a volume in Docker Compose.

Method 1: Using Relative Paths

1. Create a docker-compose.yaml file in your project directory. This file defines the services, networks, and volumes for your Docker Compose configuration.

2. Define the volumes section in the docker-compose.yaml file. This section specifies the volumes to be mounted in the containers. For example:

version: '3'
services:
  web:
    image: nginx:latest
    volumes:
      - ./data:/var/www/html

In the above example, we are mounting the ./data directory on the host machine to the /var/www/html directory inside the container.

3. Start the containers using the docker-compose up command. Docker Compose will create the necessary volume and mount the host directory to the specified path in the container.

4. Verify that the volume is mounted correctly by accessing the container and checking the contents of the mounted directory. For example, you can use the following command to access the container:

docker-compose exec web bash

Once inside the container, navigate to the mounted directory and verify the presence of the files from the host machine.

Related Article: How to Run a Docker Instance from a Dockerfile

Method 2: Using Absolute Paths

Alternatively, you can use absolute paths to mount a host directory as a volume in Docker Compose.

1. Determine the absolute path of the directory you want to mount on the host machine.

2. Update the volumes section in the docker-compose.yaml file to use the absolute path. For example:

version: '3'
services:
  web:
    image: nginx:latest
    volumes:
      - /path/to/host/data:/var/www/html

In the above example, replace /path/to/host/data with the absolute path of the directory on your host machine.

3. Start the containers using the docker-compose up command. Docker Compose will create the necessary volume and mount the host directory to the specified path in the container.

4. Verify that the volume is mounted correctly by accessing the container and checking the contents of the mounted directory. For example, you can use the following command to access the container:

docker-compose exec web bash

Once inside the container, navigate to the mounted directory and verify the presence of the files from the host machine.

Best Practices

Related Article: How to Use the Host Network in Docker Compose

- Use relative paths whenever possible to ensure your Docker Compose configuration is portable across different host machines.

- Avoid hardcoding absolute paths in your Docker Compose configuration, as they may not work on different host machines or when deploying to different environments.

- When using relative paths, ensure that the host directory you want to mount is located relative to the directory where the docker-compose.yaml file is located.

- Consider using environment variables or Docker secrets to dynamically configure the host directory path in your Docker Compose configuration. This allows for more flexibility and avoids hardcoding sensitive information.

- Regularly backup your host directories to prevent data loss in case of container or host machine failures.