Backup and restore strategies in Docker - Step-by-Step Execution

Process Flow - Backup and restore strategies

Identify data to backup

↓

Choose backup method

↓

Execute backup command

↓

Store backup safely

↓

When needed, execute restore command

↓

Verify data restored correctly

↓

END

This flow shows the steps to backup Docker data and restore it when needed, ensuring data safety.

Execution Sample

Docker

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

docker run --rm --volumes-from mycontainer -v $(pwd):/backup busybox tar xvf /backup/backup.tar -C /data

This code backs up a Docker container's data volume to a tar file and restores it from that file.

Process Table

Step	Action	Command	Result
1	Identify data volume to backup	mycontainer volume /data	Volume /data identified
2	Run backup container to create tar	docker run --rm --volumes-from mycontainer -v $(pwd):/backup busybox tar cvf /backup/backup.tar /data	backup.tar created in current directory
3	Store backup file safely	backup.tar saved locally	Backup file ready for restore
4	Run restore container to extract tar	docker run --rm --volumes-from mycontainer -v $(pwd):/backup busybox tar xvf /backup/backup.tar -C /	Data restored into /data volume
5	Verify restored data	Check container data	Data matches backup
6	Exit	No further commands	Backup and restore complete

💡 Backup and restore process ends after data verification

Status Tracker

Variable	Start	After Backup	After Restore	Final
backup.tar	Not present	Created with container data	Used to restore data	Exists as backup file
/data volume	Has original data	Data unchanged	Replaced with restored data	Data restored successfully

Key Moments - 3 Insights

Why do we use a separate container with --volumes-from to backup data?

Because the data lives inside the container volume, the backup container accesses it via --volumes-from to copy data without stopping the original container (see execution_table step 2).

What happens if we restore data to a wrong volume path?

The restore command extracts files to the specified path. If wrong, data won't be restored correctly, causing mismatch during verification (see execution_table step 4 and 5).

Why do we mount the current directory to /backup in the container?

Mounting $(pwd) to /backup lets the container write the backup.tar file to the host machine, making it accessible outside the container (see execution_table steps 2 and 4).

Visual Quiz - 3 Questions

Look at the execution table, at which step is the backup.tar file created?

A Step 1

B Step 2

C Step 4

D Step 5

💡 Hint

Check the 'Result' column for the step where backup.tar is created.

According to the variable tracker, what is the state of /data volume after restore?

A Replaced with restored data

B Has original data

C Data unchanged

D Data lost

💡 Hint

Look at the 'After Restore' column for /data volume in variable_tracker.

If we skip mounting $(pwd) to /backup, what happens to the backup file?

A Backup fails with error

B It is saved on the host machine

C It is saved inside the container and lost after it exits

D Backup file is saved in /data volume

💡 Hint

Refer to key_moments about mounting current directory for backup file accessibility.

Concept Snapshot

Backup and restore Docker volumes:
- Use 'docker run --volumes-from' to access container volumes
- Mount host dir to container to save backup files
- Use tar to archive and extract volume data
- Verify data after restore
- Keep backups safe and test restores regularly

Full Transcript

This lesson shows how to backup and restore Docker container data volumes. First, identify the volume to backup. Then run a temporary container with --volumes-from to access the volume and mount the current directory to save the backup tar file. Use tar commands inside the container to create and extract backups. After restoring, verify the data matches the original. This method keeps data safe and allows recovery if needed.

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