Container disk usage management in Docker - Practice Problems & Coding Challenges

Challenge - 5 Problems

💻 Command Output

intermediate

Check disk space used by Docker images

What is the output of the command docker system df -v regarding image sizes?

Docker

docker system df -v

A Shows Docker daemon logs related to disk usage

B Only lists running containers with their disk usage

C Displays network usage statistics for Docker containers

D Shows detailed disk usage including images, containers, volumes, and build cache with sizes

💡 Hint

Think about which command gives a detailed summary of disk usage for all Docker objects.

The docker system df -v command provides a verbose summary of disk usage by images, containers, volumes, and build cache. It helps identify which objects consume the most space.

❓ Troubleshoot

intermediate

Identify cause of disk space not freeing after container removal

You removed a Docker container but disk space did not increase. What is the most likely reason?

A The container was not actually stopped before removal

B Docker daemon needs to be restarted to free space

C The container's volumes are still present and consuming space

D Docker images are automatically deleted with container removal

💡 Hint

Think about what Docker volumes do when containers are deleted.

Removing a container does not delete its associated volumes by default. Volumes store persistent data and remain on disk, consuming space until explicitly removed.

❓ Configuration

advanced

Configure Docker to limit container log size

Which Docker daemon configuration snippet correctly limits container log files to 10MB with 3 rotated files?

A

{
  "log-driver": "json-file",
  "log-opts": {
    "max-size": "100m",
    "max-file": "1"
  }
}

B

{
  "log-driver": "json-file",
  "log-opts": {
    "max-size": "10m",
    "max-file": "3"
  }
}

C

{
  "log-driver": "syslog",
  "log-opts": {
    "max-size": "10m",
    "max-file": "3"
  }
}

D

{
  "log-driver": "journald",
  "log-opts": {
    "max-size": "10m",
    "max-file": "3"
  }
}

💡 Hint

The default log driver that supports size and file rotation is json-file.

The json-file log driver supports max-size and max-file options to limit log file size and number of rotated files. Other drivers like syslog or journald do not support these options.

🔀 Workflow

advanced

Steps to safely clean up unused Docker resources

Which option lists the correct sequence of commands to safely clean up unused containers, images, volumes, and build cache?

A docker container prune → docker image prune → docker volume prune → docker builder prune

B docker volume prune → docker container prune → docker builder prune → docker image prune

C docker system prune -a → docker container prune → docker volume prune → docker builder prune

D docker builder prune → docker image prune → docker container prune → docker volume prune

💡 Hint

Start by removing stopped containers, then images, volumes, and finally build cache.

The recommended order is to prune stopped containers first, then unused images, followed by unused volumes, and finally the build cache. This order avoids dependency conflicts and safely frees disk space.

✅ Best Practice

expert

Prevent excessive disk usage by containers in production

Which practice best prevents excessive disk usage by Docker containers in a production environment?

A Use read-only root filesystem for containers and mount writable volumes only where needed

B Disable Docker logging to prevent log files from growing

C Run containers with unlimited disk quota to avoid failures

D Avoid using volumes and store all data inside containers

💡 Hint

Think about controlling where data is written to limit disk growth.

Using a read-only root filesystem limits container writes to only designated volumes. This prevents unexpected disk usage growth inside containers. Unlimited disk quota or disabling logs can cause issues. Avoiding volumes leads to data loss and harder management.