Optimize Docker Images

Analyze Docker image layers and apply optimizations for size and build performance.

Analysis Steps

1. Check Current Image

docker images {image_name} --format "table {{.Repository}}\t{{.Tag}}\t{{.Size}}"

2. Analyze Layers

docker history {image_name}:{tag} --no-trunc --format "table {{.Size}}\t{{.CreatedBy}}"

3. Read Dockerfile

Glob: Dockerfile, Dockerfile.*

Read and analyze the current Dockerfile structure.

Optimization Checks

Size Optimizations

Check	Optimization
Base image	Switch to alpine/slim/distroless
Multi-stage	Convert single-stage to multi-stage
Dev deps in runtime	Remove build tools from final stage
Package cache	Clean apt/apk cache in same RUN layer
Unnecessary files	Add to .dockerignore
Layer count	Combine related RUN commands

Build Speed Optimizations

Check	Optimization
Layer ordering	Move frequently changing layers last
Cache mounts	Add --mount=type=cache for package managers
Dependency caching	Copy lock files before source code
BuildKit features	Enable DOCKER_BUILDKIT=1

Caching Optimizations

Check	Optimization
Lock file first	COPY package.json before COPY .
Source last	Application code copied last
Build cache	Use --mount=type=cache

Workflow

1. Analyze Current State

Gather image size, layer count, and Dockerfile content.

2. Identify Optimizations

Compare against checklist and identify applicable improvements.

3. Present Findings

Show before/after comparison for each optimization with estimated impact.

4. Ask User

Via AskUserQuestion:

• "Apply all optimizations" - Rewrite Dockerfile
• "Apply selected" - Choose which to apply
• "Report only" - No changes

5. Apply Changes

If requested, rewrite Dockerfile with optimizations applied.

6. Generate Report

Use optimization-report.md template.

Common Optimizations

Multi-stage Conversion

Before:

FROM python:3.12
COPY . .
RUN pip install -r requirements.txt
CMD ["python", "main.py"]

After:

FROM python:3.12-slim AS builder
COPY requirements.txt .
RUN pip install --no-cache-dir -r requirements.txt

FROM python:3.12-slim
COPY --from=builder /usr/local/lib/python3.12/site-packages /usr/local/lib/python3.12/site-packages
COPY . .
CMD ["python", "main.py"]

Cache Mount Addition

Before:

RUN pip install -r requirements.txt

After:

RUN --mount=type=cache,target=/root/.cache/pip \
    pip install -r requirements.txt

Base Image Switch

From	To	Savings
python:3.12	python:3.12-slim	~700MB
node:20	node:20-slim	~600MB
ubuntu:22.04	debian:bookworm-slim	~50MB