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Docker: Bind mounts

When we run containers, the filesystem is isolated from the host machine. This means that any changes made to the filesystem inside the container will not affect the host filesystem, and vice versa. However, there are times when you may want to share files between the host and the container. This is where bind mounts and volumes come into play.

Bind mounts​

A bind mount is a mapping between a host file or directory and a container file or directory. This allows you to share files between the host and the container, and any changes made to the files will be reflected in both places.

Step 1: Creating a directory to share​

Make sure that you have stopped the nginx container, that you have previously created.

First, we need to create a directory that we want to share with the container. Open up your terminal and run the following command:

mkdir -p tek2/nginx-example

This will create the directory tek2/nginx-example on your host machine.

Step 2: Creating a bind mount​

To create a bind mount, you can use the -v option with the docker run command:

docker run -d --name my-nginx -p 8090:80 -v ./tek2/nginx-example:/usr/share/nginx/html:ro nginx

The ./tek2/nginx-example tells that we want to map everything inside the nginx-example directory to the /usr/share/nginx/html directory inside the container. The :ro option (optional) makes the container's view of the files read-only - ie. the files cannot be modified from within the container.

Any files placed in the host directory (./tek2/nginx-example) will be accessible inside the container.

Step 3: Adding files to the shared directory​

Now that we have our bind mount set up, we can add files to the ./tek2/nginx-example directory on the host machine. These files will be automatically available inside the container at /usr/share/nginx/html.

Add an index.html file to the ./tek2/nginx-example directory with the following content:

<!DOCTYPE html>
    <html>
        <head>
            <title>My Nginx Page</title>
        </head>
        <body>
            <h1>Hello from Nginx using Docker!</h1>
    </body>
</html>

To test that the bind mount is working, you can open a web browser and navigate to http://localhost:8090. You should see the contents of the index.html file that you created earlier (if not try opening the browser in incognito mode).

Volumes​

Volumes are a more flexible way to manage data in Docker. Unlike bind mounts, which are tied to a specific host path, volumes are managed by Docker and can be easily shared between containers.

Step 1: Creating a volume​

To create a volume, you can use the docker volume create command:

docker volume create nginx-data

You can see a list of all your volumes by running the following command:

docker volume ls

Step 2: Using the volume​

Once the volume is created, you can use it with the -v option when running a container:

docker run --rm -d -p 8095:80 --name web -v nginx-data:/usr/share/nginx/html nginx

In this example, the nginx-data volume is mounted to the /usr/share/nginx/html directory inside the container.

Step 3: Adding files to the volume​

Now that we have our volume set up, we can add files to the nginx-data volume. You can do this by running a temporary container that mounts the volume and allows you to copy files into it:

docker cp ./tek2/nginx-example/index.html web:/usr/share/nginx/html/

This will add the file to the nginx-data volume.

Verify by opening a web browser and navigating to http://localhost:8095. You should see the contents of the index.html file that you created earlier (if not try opening the browser in incognito mode).

Step 4: Restarting the container​

Stop the container:

docker stop web

Now run the container again:

docker run --rm -d -p 8095:80 --name web -v nginx-data:/usr/share/nginx/html nginx

Note that the contents of the nginx-data volume will persist even if the container is stopped or removed.