🚢 Day 09: Docker Export/Import & Save/Load Guide

Welcome to this hands-on guide for Exporting, Importing, Saving, and Loading Docker Containers and Images. Perfect for backups, sharing, or migrating environments! 🎯

🐳 Docker Image & Container Management Commands Summary

• 🛬 docker import – Creates an image from a tarball (e.g., from docker export).

• 📦 docker load – Loads an image from a tar archive (e.g., from docker save).

• 🛫 docker export – Exports a container’s filesystem as a tar archive.

• 💾 docker save – Saves one or more images to a tar archive.

• 📝 docker commit – Creates a new image from a container’s changes.

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🎬 Video Demonstration

⚖️ Comparison: docker export vs docker save vs docker commit

⚖️ Difference Between docker import vs docker load

🧠 TL;DR

• Use docker import if you have an exported **container filesystem** (export`).

• Use docker **load** if you have a saved image archive (save).

• Use docker **commit** if you want to turn a live container into a new image, preserving its current state.

🔧 Prepare Environment for the Demo

# Run Day 08 Container for demo
DAY=day09
mkdir -p $DAY && cd $DAY 
echo "Welcome to DevOps in Action" | sudo tee ./index.html
docker run -itd --name=$DAY -p 8085:80 -v /home/user/$DAY:/usr/share/nginx/html nginx:alpine
http://192.168.1.22:8085/

# Example container ID or name
container_name="day09"
or 
container_name="d40fa919ae31"

📦 1. Exporting and Importing Containers

## 🔹 Export a Running or Paused Container
# You can export a container's filesystem into a `.tar` archive.
docker export $container_name | gzip > $container_name.tgz
# 📝 This only includes the filesystem, not image layers or history.

## 🔹 Import an Exported Container
gunzip -c $container_name.tgz | docker import - mynewimage:latest
docker image history mynewimage
# > 🔁 This creates a new image from the tarball, useful for backups or transferring containers.
# Test image
docker run -itd --name=testimage -p 8090:80 mynewimage:latest
# you got error here so see above table for understanding.
# 📚 Metadata (e.g. CMD, ENV) ❌ Not preserved

## 🔹 Commit a Container to Preserve State with Metadata
docker commit -a "Ansari" $container_name preserve:v1
docker image history preserve:v1
# 📝 This creates a new image named 'preserve:v1' from the current state of the container.
#     - Includes the current filesystem state
#     - Retains metadata like CMD, ENV if the base image had it
#     - Useful for turning a modified container into a reusable image

## 🔹 Run a Container from the Committed Image
docker run -itd --name=testimage -p 8090:80 preserve:v1
docker logs testimage
http://192.168.1.22:8090/

# 🟢 This runs a container from the newly committed image.

🧊 2. Saving and Loading Docker Images

## 🔹 Save Docker Image to `.tar`
docker save -o ubuntu_latest.tar ubuntu:latest
ls -alsh ubuntu*
# Or compressed:
docker save ubuntu:latest | gzip > ubuntu_latest.tar.gz
du -sh ubuntu*

## 🔹 Load Docker Image from `.tar`
docker image remove ubuntu:latest
docker images | grep ubuntu

docker load -i ubuntu_latest.tar
docker images | grep ubuntu
# Or for `.gz`:
docker image remove ubuntu:latest
docker load < ubuntu_latest.tar.gz
docker images | grep ubuntu

docker image history ubuntu

🔍 Visual Analogy

⚙️ 3. Exporting All Stopped Containers

Let’s export all exited containers with their names and IDs.

# First clean folder
rm -rf *

# Make a stopped container
docker stop $container_name

# Run hello world
docker run hello-world

# Exporting All Stopped Containers
while read image container_id; do
  image_sanitized=$(echo "$image" | tr '/:' '_') # handles slashes and tags
  docker export "$container_id" > "${image_sanitized}-${container_id}.tar"
done < <(docker ps -a -f status=exited --format '{{.Image}} {{.ID}}')

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🚀 4. Import Containers as Versioned Images

To convert exported containers into images with version tags:

for file in *.tar; do
  base=$(basename "$file" .tar)
  # e.g., "hello-world-53af1e9021bf"
  image_name="${base%-*}"      # remove the last dash + ID
  # container_id="${base##*-}"   # extract only the container ID
  # Optional: replace underscores back to slashes/colons if needed
  # image_name=$(echo "$image_name" | tr '_' '/')
  # docker import "$file" "${image_name}:${container_id}"
  docker import "$file" "${image_name}:latest"
done

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🏷️ 5. Save All Images to .tar

Want to back up all images?

# First clean folder
rm -rf *

# Save All Images to `.tar`
docker save $(docker images | sed '1d' | awk '{print $1 ":" $2 }') -o allinone.tar

# To avoid malformed names dangling images if you have:
docker images --format "{{.Repository}}:{{.Tag}}" | grep -v "<none>" | xargs docker save -o allinone.tar

# Export it seprately
docker images --format "{{.Repository}}:{{.Tag}}" | grep -v "<none>" | while read image; do
  filename=$(echo "$image" | sed 's/[\/:]/_/g').tar
  docker save "$image" -o "$filename"
done

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📤 6. Load All Saved Images

Load every .tar file in the current directory:

# Stop all containers
docker rm -f $(docker ps -aq)

# Remove all images
docker rmi -f $(docker images -q)

# Load Saved Images
docker load -i allinone.tar

# Load All Saved Images seprately
for tarfile in *.tar; do
  echo "Loading $tarfile..."
  docker load -i "$tarfile"
done

# Verify it
docker images

# Test image
docker run -itd --name=test -p 8080:80 nginx:alpine

# Test Nginx
http://192.168.1.22:8080/

🛠️ 7. Troubleshooting

• Error: No such container:

  • Ensure the container exists (docker ps -a).

• Error: Invalid tar header:

  • Verify the tarball isn’t corrupted (tar -tvf file.tar).

• Large tarball sizes:

  • Use compression (gzip) or clean up unnecessary container data.

• Imported image not running:

  • Check if the image requires specific entrypoint/cmd (docker inspect).

💡 Best Practices & Tips

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🔗 Additional Resources

• 📘 Docker Documentation: Export

• 📘 Docker Documentation: Import

• 📘 Docker Documentation: Save

• 📘 Docker Documentation: Load

• 📘 Docker Documentation: Commit