Image Size Audit

Intermediate10 min

Analyze Docker image layers to understand what is taking up space and identify optimization opportunities.

Prerequisites

-Docker installed

Steps

List images sorted by size

See all images and their sizes, largest first.

$ docker images --format '{{.Size}}\t{{.Repository}}:{{.Tag}}' | sort -hr | head -20

Inspect image layer sizes

Break down an image into its constituent layers to see what each adds.

$ docker history myapp:latest --format 'table {{.Size}}\t{{.CreatedBy}}' --no-trunc

Use dive for interactive layer analysis

Run dive to explore each layer's filesystem changes interactively.

$ docker run --rm -it -v /var/run/docker.sock:/var/run/docker.sock wagoodman/dive myapp:latest

Dive shows wasted space, efficiency scores, and lets you browse each layer's file tree.

Find dangling images consuming space

Identify untagged images that are using disk space.

$ docker images -f 'dangling=true' --format 'table {{.ID}}\t{{.Size}}\t{{.CreatedSince}}'

Check total Docker disk usage

See a summary of disk space used by images, containers, volumes, and build cache.

$ docker system df -v

Full Script

full-script.sh

#!/bin/bash
# Image Size Audit
set -euo pipefail

echo "=== Docker Disk Usage Summary ==="
docker system df

echo ""
echo "=== Top 10 Largest Images ==="
docker images --format '{{.Size}}\t{{.Repository}}:{{.Tag}}' | sort -hr | head -10

echo ""
echo "=== Dangling Images ==="
docker images -f 'dangling=true' --format '{{.ID}}\t{{.Size}}' | head -10 || echo "None"

echo ""
echo "=== Optimization Tips ==="
echo "1. Use multi-stage builds"
echo "2. Choose smaller base images (alpine, slim, distroless)"
echo "3. Combine RUN commands with &&"
echo "4. Clean package caches in the same layer: rm -rf /var/cache/apt/*"
echo "5. Use .dockerignore to exclude build artifacts"

FAQ

Discussion

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#!/bin/bash # Image Size Audit set -euo pipefail echo "=== Docker Disk Usage Summary ===" docker system df echo "" echo "=== Top 10 Largest Images ===" docker images --format '{{.Size}}\t{{.Repository}}:{{.Tag}}' | sort -hr | head -10 echo "" echo "=== Dangling Images ===" docker images -f 'dangling=true' --format '{{.ID}}\t{{.Size}}' | head -10 || echo "None" echo "" echo "=== Optimization Tips ===" echo "1. Use multi-stage builds" echo "2. Choose smaller base images (alpine, slim, distroless)" echo "3. Combine RUN commands with &&" echo "4. Clean package caches in the same layer: rm -rf /var/cache/apt/*" echo "5. Use .dockerignore to exclude build artifacts"