🚀 Day 08: Copy Files between Host and Docker Containers 🐳

Docker Zero to Hero Series - Copying Like a Pro

Welcome to Day 08 of our Docker Zero to Hero 🐳 series!
Today we’re diving into how to copy files ⬅️ From Docker Container to Host and ➡️ From Host to Docker Container.

Let’s break it down step-by-step with examples for:

✅ Single files
✅ Multiple files and directories
✅ Using docker cp
✅ Using docker exec
✅ Exporting config from a temp container
✅ Advanced tricks & troubleshooting

🎬 Video Demonstration

🔧 Set Example Container Name

# Run Day 08 Container for demo
docker run -itd --name=day08 -p 8085:80 -v /home/user/html:/usr/share/nginx/html nginx:latest
mkdir -p day08

# Example container ID or name
container_name="day08"
or 
container_name="d40fa919ae31"

🧱 1. Copying Files using docker cp (Simple & Powerful)

📥 Copy from Container ➡️ to Host

# Inspect container path/colume/bind-mount
docker inspect $container_name | jq '.[0].Mounts[] | select(.Type == "bind" or .Type == "volume") | {Type, Source, Destination}'

# Single file
docker cp $container_name:/path/in/container/file.txt /path/on/host/file.txt

# Example:
mkdir -p /home/user/html_file
docker cp $container_name:/usr/share/nginx/html/index.html /home/user/html_file/index.html
cat /home/user/html_file/index.html

# Directory (recursively)
docker cp $container_name:/usr/share/nginx/html /home/user/html_backup
ls -alsh /home/user/html_backup

📤 Copy from Host ➡️ to Container

# Single file
docker cp /path/on/host/file.txt $container_name:/path/in/container/file.txt

# Example:
docker cp /home/user/html_file/index.html $container_name:/usr/share/nginx/html/index.html

# Directory (recursively)
docker cp /home/user/html_backup $container_name:/usr/share/nginx/html
docker exec $container_name ls -alsh /usr/share/nginx/html

🗃️ 2. Copying Multiple Files or Directories

# Copy multiple files (from host)
docker cp ./test.sh $container_name:/usr/share/nginx/html
docker cp ./Desktop $container_name:/usr/share/nginx/html
docker exec $container_name ls -alsh /usr/share/nginx/html

✅ Tip: Use . to copy all contents of a directory

docker cp ./Desktop/. $container_name:/usr/share/nginx/html

🧰 3. Backup and Restore Hidden Files (.dotfiles)

📤 Backup from Container

docker cp $container_name:/.dockerenv ./day08/.dockerenv
ls -alsh ./day08/.dockerenv

📥 Restore to Container

docker cp ./day08/.dockerenv $container_name:/.dockerenv_nedw
docker exec $container_name ls -alsh /

⚠️ Make sure to include the trailing . to copy contents, not the directory itself!

📦 4. Export Config Files from a Image

# Example: Exporting grafana.ini from Grafana container
docker run --rm -d --name temp-grafana grafana/grafana && docker cp temp-grafana:/etc/grafana/grafana.ini $PWD/day08/grafana.ini && docker stop temp-grafana
ls -alsh ./day08/

✅ 5. Safer Approach – Bind Mounts or Volumes (Recommended)

This is the safer and recommended way to interact with container files, using bind mounts or Docker volumes.

# Example of editing content via bind mount or volume
docker inspect $container_name | grep -A5 Mounts

# Modify file on HOST (affects container if using bind mount)
echo "Welcome to DevOps in Action" | sudo tee /home/user/html/index.html

# Access in browser
http://192.168.1.22:8085/

⚠️ 6. Advanced (Not Recommended) – Direct Access to Docker Filesystem

This method accesses container files directly via Docker’s internal storage (e.g., OverlayFS). Use only for advanced troubleshooting or backup purposes. It bypasses Docker’s APIs and may corrupt data or containers if misused.

# Create container
docker run -d --name test-nginx -p 8086:80 nginx

# Get container's merged directory path
CONT_PATH=$(docker inspect test-nginx --format='{{.GraphDriver.Data.MergedDir}}')

# 🔽 Copy file from container to host
sudo cp $CONT_PATH/usr/share/nginx/html/index.html $PWD/day08/index.html
cat $PWD/day08/index.html

# Access in browser
http://192.168.1.22:8086/

# 🔼 Copy file from host into container's filesystem (dangerous)
echo "Welcome to DevOps in Action" | sudo tee "$PWD/day08/index.html"
sudo cp $PWD/day08/index.html $CONT_PATH/usr/share/nginx/html/index.html 
sudo cat $CONT_PATH/usr/share/nginx/html/index.html

⚠️ Warning: Direct manipulation of container storage may cause data corruption. Always prefer Docker CLI commands or volume mounts unless absolutely necessary.

✅ Summary Table

📌 Final Tips

• Always verify file permissions after copying.

• Avoid copying into running containers' system paths (/bin, /lib) unless you know what you're doing.

• Use docker volume if frequent file sharing is needed.

🔗 Additional Resources

• 📘 Docker cp command