How to Share Data Between Docker Containers

There are two main ways to share data:

1. A Docker volume. Docker manages the storage, and the data stays after containers are removed.
2. A host directory (bind mount). You mount a folder of the host into the containers.

Method 1: Share data with an independent volume

Step 1: Create the volume

docker volume create shared_vol

Look at its details:

docker volume inspect shared_vol

Step 2: Start the first container

docker run -it --name cont1 -v shared_vol:/shared_vol ubuntu

Step 3: Create a file in the shared volume (inside cont1)

echo "Creating shared file" >> /shared_vol/file.txt

Leave the container with exit.

Step 4: Start the second container

docker run -it --name cont2 -v shared_vol:/shared_vol ubuntu

Step 5: Check the data

cat /shared_vol/file.txt

The second container sees the file made by the first one.

Method 2: The data stays after containers are removed

Step 1: Remove the containers

docker rm cont1

docker rm cont2

Step 2: Start a new container with the same volume

docker run -it --name cont3 -v shared_vol:/shared_vol ubuntu

Run cat /shared_vol/file.txt. The file is still there, because the volume is separate from the containers.

Method 3: Share a host directory

Step 1: Create a folder on the host

mkdir shared_dir

Step 2: Start a container that mounts it

On Linux or macOS use the full path:

docker run -it --name cont-1 -v "$(pwd)/shared_dir":/shared_dir ubuntu

On Windows use a path like this:

docker run -it --name cont-1 -v C:/Users/YourName/Documents/shared_dir:/shared_dir ubuntu

Step 3: Create a file in the container

echo "file is created in the shared directory" >> /shared_dir/file.txt

Step 4: Check it on the host

Open the shared_dir folder on the host. The file file.txt is there.

Step 5: Start a second container with the same folder

docker run -it --name cont-2 -v "$(pwd)/shared_dir":/shared_dir ubuntu

Both containers now read and write the same host folder.

Read-only sharing

Add :ro to give a container read-only access:

docker run -it -v shared_vol:/shared_vol:ro ubuntu

Docker Compose

services:
  app1:
    image: ubuntu
    command: sleep infinity
    volumes:
      - shared_vol:/shared_vol
  app2:
    image: ubuntu
    command: sleep infinity
    volumes:
      - shared_vol:/shared_vol

volumes:
  shared_vol:

Which method to use

• Volume: best for app data, managed by Docker, works on every platform.
• Host directory: best when you want to edit files from the host, for example source code.

Quick recap

• docker volume create and -v volume:/path for volumes.
• -v /host/path:/path for a host folder.