Backup and restore strategies in Docker - Commands & Configuration

Introduction

Backing up data means saving a copy of important information so you don't lose it. Restoring means putting that saved data back if something goes wrong. In Docker, this helps protect your app's data stored in containers or volumes.

When you want to save your database data before updating your app container

When you need to move your app data from one server to another

When you want to protect your files stored in Docker volumes from accidental deletion

When you want to create a snapshot of your app's state before testing new features

When you want to recover your app data after a container crash or failure

Commands

This command creates a backup of the /data directory inside the 'my-app-container' container. It uses a temporary busybox container to access the volume and saves the backup.tar file to your current folder.

Terminal

docker run --rm --volumes-from my-app-container -v $(pwd):/backup busybox tar cvf /backup/backup.tar /data

Expected Output

data/

data/file1.txt

data/file2.txt

→

--volumes-from - Mounts volumes from the specified container

→

-v - Binds a host directory to the container for saving the backup

→

--rm - Removes the temporary container after the command finishes

This command restores the backup.tar file from your current folder into the Docker volume named 'my-app-data'. It uses a temporary busybox container to extract the files into the volume.

Terminal

docker run --rm -v $(pwd):/backup -v my-app-data:/data busybox tar xvf /backup/backup.tar -C /data

Expected Output

data/

data/file1.txt

data/file2.txt

→

-v - Binds host folder and Docker volume to the container

→

--rm - Removes the temporary container after restoring

Lists all Docker volumes on your system to verify that the volume 'my-app-data' exists before restoring data.

Terminal

docker volume ls

Expected Output

DRIVER    VOLUME NAME

local     my-app-data

Shows all containers to check if your app container is running or stopped before backup or restore.

Terminal

docker ps -a

Expected Output

CONTAINER ID   IMAGE          COMMAND                  CREATED          STATUS                      PORTS     NAMES

abc123def456   my-app-image   "/bin/sh -c 'npm start'" 10 minutes ago   Up 10 minutes                         my-app-container

Key Concept

If you remember nothing else from this pattern, remember: use a temporary container with volume mounts to safely backup and restore Docker volumes.

Common Mistakes

Trying to copy files directly from a running container without using volume mounts

This can miss data stored in volumes or cause inconsistent backups

Use a temporary container with --volumes-from or mount the volume directly to access all data

Not removing the temporary container after backup or restore

Leads to leftover containers cluttering your system

Use the --rm flag to automatically clean up temporary containers

Restoring backup files to the wrong volume or directory

Data will not be restored correctly and app may fail

Double-check volume names and paths before running restore commands

Summary

Use a temporary container with volume mounts to create a backup archive of your app data.

Verify your Docker volumes and containers before backup and restore operations.

Restore data by extracting the backup archive into the correct Docker volume using a temporary container.

Practice

1. What is the main purpose of backing up Docker volumes?

easy

A. To update Docker to the latest version

B. To speed up container startup time

C. To reduce the size of Docker images

D. To save important data so it can be restored later

Solution

1. Step 1: Understand backup purpose

   Backing up means saving data safely so it is not lost.

2. Step 2: Relate to Docker volumes

   Docker volumes store important data outside containers, so backing them up protects that data.

3. Final Answer:

   To save important data so it can be restored later -> Option D

4. Quick Check:

   Backup = Save data safely [OK]

Hint: Backup means saving data to prevent loss [OK]

Common Mistakes:

• Confusing backup with speeding up containers
• Thinking backup reduces image size
• Assuming backup updates Docker itself

2. Which of the following commands correctly creates a backup of a Docker volume named mydata using tar?

easy

A. docker save mydata > /backup/mydata.tar

B. docker run --rm -v mydata:/data -v /backup:/backup busybox tar cvf /backup/mydata.tar /data

C. docker volume backup mydata /backup/mydata.tar

D. docker run --rm -v mydata:/data busybox tar xvf /backup/mydata.tar /data

Solution

1. Step 1: Identify backup command syntax

   Backing up a volume uses tar cvf to create an archive of the volume data.

2. Step 2: Check each option

   docker run --rm -v mydata:/data -v /backup:/backup busybox tar cvf /backup/mydata.tar /data runs a container mounting the volume and backup directory and uses tar cvf to save data. docker run --rm -v mydata:/data busybox tar xvf /backup/mydata.tar /data extracts instead of creating. docker volume backup mydata /backup/mydata.tar is invalid Docker syntax. docker save mydata > /backup/mydata.tar saves an image, not a volume.

3. Final Answer:

   docker run --rm -v mydata:/data -v /backup:/backup busybox tar cvf /backup/mydata.tar /data -> Option B

4. Quick Check:

   Backup = tar cvf inside container [OK]

Hint: Use tar cvf to create backup archive inside container [OK]

Common Mistakes:

• Using tar xvf which extracts instead of backs up
• Trying non-existent docker volume backup command
• Using docker save which backs up images, not volumes

3. What will be the result of running this command?

docker run --rm -v mydata:/data -v /backup:/backup busybox tar xvf /backup/mydata.tar -C /data

medium

A. It restores the volume data from the backup archive

B. It creates a backup archive of the volume data

C. It lists the contents of the backup archive without extracting

D. It deletes the volume data

Solution

1. Step 1: Understand the tar command

   The tar xvf command extracts files from an archive.

2. Step 2: Analyze the Docker command

   The command mounts the volume mydata at /data and the backup directory at /backup and extracts the archive /backup/mydata.tar into it using -C /data.

3. Final Answer:

   It restores the volume data from the backup archive -> Option A

4. Quick Check:

   tar xvf = extract = restore [OK]

Hint: tar xvf extracts files, so it restores data [OK]

Common Mistakes:

• Confusing xvf with cvf (backup vs restore)
• Thinking it lists archive contents
• Assuming it deletes data

4. You tried to restore a Docker volume backup with this command:

docker run --rm -v mydata:/data busybox tar cvf /backup/mydata.tar /data

But the backup file is empty. What is the likely mistake?

medium

A. Using tar cvf instead of tar xvf to restore

B. Mounting the volume at the wrong path

C. Creating a backup instead of restoring

D. Not specifying the -C option to change directory

Solution

1. Step 1: Identify the command purpose

   tar cvf creates an archive (backup), not restore.

2. Step 2: Understand the mistake

   The command tries to create a backup but is used when intending to restore, so the backup file is empty or incorrect.

3. Final Answer:

   Creating a backup instead of restoring -> Option C

4. Quick Check:

   tar cvf = backup, not restore [OK]

Hint: tar cvf creates backup; use tar xvf to restore [OK]

Common Mistakes:

• Confusing backup and restore tar options
• Mounting volume incorrectly
• Forgetting to use -C option

5. You want to backup multiple Docker volumes data1 and data2 into separate tar files and then restore them later. Which sequence of commands correctly achieves this?

hard

A. docker run --rm -v data1:/data -v /backup:/backup busybox tar cvf /backup/data1.tar /datadocker run --rm -v data2:/data -v /backup:/backup busybox tar cvf /backup/data2.tar /datadocker run --rm -v data1:/data -v /backup:/backup busybox tar xvf /backup/data1.tar -C /datadocker run --rm -v data2:/data -v /backup:/backup busybox tar xvf /backup/data2.tar -C /data

B. docker volume backup data1 /backup/data1.tardocker volume backup data2 /backup/data2.tardocker volume restore data1 /backup/data1.tardocker volume restore data2 /backup/data2.tar

C. docker save data1 > /backup/data1.tardocker save data2 > /backup/data2.tardocker load < /backup/data1.tardocker load < /backup/data2.tar

D. docker export data1 > /backup/data1.tardocker export data2 > /backup/data2.tardocker import /backup/data1.tardocker import /backup/data2.tar

Solution

1. Step 1: Backup each volume separately

   Use tar cvf inside a container mounting each volume and the backup directory to create separate tar files.

2. Step 2: Restore each volume separately

   Use tar xvf with -C option inside a container mounting each volume and the backup directory to extract data back.

3. Step 3: Verify other options

   Other sequences use invalid Docker commands like docker volume backup, commands meant for images like docker save/load, or for containers like docker export/import.

4. Final Answer:

   docker run --rm -v data1:/data -v /backup:/backup busybox tar cvf /backup/data1.tar /data<br>docker run --rm -v data2:/data -v /backup:/backup busybox tar cvf /backup/data2.tar /data<br>docker run --rm -v data1:/data -v /backup:/backup busybox tar xvf /backup/data1.tar -C /data<br>docker run --rm -v data2:/data -v /backup:/backup busybox tar xvf /backup/data2.tar -C /data -> Option A

5. Quick Check:

   Backup and restore volumes with tar inside containers [OK]

Hint: Backup and restore each volume with tar inside containers [OK]

Common Mistakes:

• Using docker save/load which works for images, not volumes
• Using non-existent docker volume backup commands
• Confusing export/import with volume backup