Docker: Day 7

What Are Bind Mounts?

A bind mount is a powerful feature of Docker that allows a file or directory on the host machine to be mounted into a container. This enables seamless interaction between the host system and the Docker container. Below are some key characteristics of bind mounts:

1. Mapping Host Files to Container Files:

   • Bind mounts allow specific files or directories from the host machine to be mapped to the corresponding files or directories in the container.

2. Flexible Storage Location:

   • Unlike Docker volumes, bind mounts can be stored anywhere on the host system.

3. Direct Modifications:

   • Both Docker containers and non-Docker processes on the host machine can modify files in the bind mount at any time.

4. Unsupported in Dockerfile:

   • Bind mounts cannot be used within a Dockerfile. They are exclusively configured during the docker run command.

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Good Use Cases for Bind Mounts

Bind mounts are especially useful in the following scenarios:

1. Sharing Configuration Files:

   • Share configuration files from the host machine to one or more containers to ensure consistent application behavior.

2. Development and Testing Environments:

   • Share source code or build artifacts between a development environment on the Docker host and the container. This allows developers to edit files on the host machine and see changes reflected in real time within the container.

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Starting NGINX with a Bind Mount

To understand bind mounts in action, let’s use a practical example by starting an NGINX container with a bind mount. This will demonstrate how to map a directory from the host system to the container.

Steps to Start NGINX with a Bind Mount:

1. Run the NGINX Container: Use the following Docker command to start an NGINX container and bind mount the current directory ($(pwd)) to /app in the container:

   docker container run -d --name nginx --mount type=bind,source=$(pwd),target=/app nginx

• --name nginx: Names the container nginx.
• --mount type=bind: Specifies the type of mount as bind.
• source=$(pwd): Defines the source directory on the host machine as the current working directory.
• target=/app: Maps the source directory to /app inside the container.

1. Verify the Bind Mount:

   • Use docker inspect to confirm that the bind mount has been successfully created:

    docker inspect nginx
   

• Check the Mounts section in the output to ensure the mapping between the host and container directories.

1. Interact with the Mounted Directory:
   • Any changes made to the files in the host directory will immediately reflect inside the container under the /app directory, and vice versa.

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