dockerfile-optimizer

Dockerfile Optimizer

Optimize Docker images for size, speed, and security.

Quick Start

Analyze current Dockerfile:

docker build -t myapp .
docker images myapp
# Note the size, then optimize

Instructions

Step 1: Analyze Current Dockerfile

Review for optimization opportunities:

• Base image choice
• Layer structure
• Build dependencies
• Caching strategy
• Security practices

Step 2: Optimize Base Image

Choose minimal base:

# Before: Large base
FROM ubuntu:22.04  # ~77MB

# After: Minimal base
FROM alpine:3.18   # ~7MB
# or
FROM node:18-alpine  # ~170MB vs node:18 ~990MB

Use specific tags:

# Bad: Unpredictable
FROM node:latest

# Good: Specific version
FROM node:18.17-alpine3.18

Step 3: Implement Multi-Stage Builds

For compiled languages:

# Before: Single stage
FROM golang:1.21
WORKDIR /app
COPY . .
RUN go build -o app
CMD ["./app"]
# Result: ~800MB

# After: Multi-stage
FROM golang:1.21-alpine AS builder
WORKDIR /app
COPY . .
RUN go build -o app

FROM alpine:3.18
COPY --from=builder /app/app /app
CMD ["/app"]
# Result: ~15MB

Step 4: Optimize Layer Caching

Order by change frequency:

# Bad: Code changes invalidate all layers
FROM node:18-alpine
COPY . .
RUN npm install
CMD ["node", "server.js"]

# Good: Dependencies cached separately
FROM node:18-alpine
WORKDIR /app
COPY package*.json ./
RUN npm ci --only=production
COPY . .
CMD ["node", "server.js"]

Step 5: Combine and Minimize Layers

Reduce layer count:

# Before: Multiple layers
RUN apt-get update
RUN apt-get install -y curl
RUN apt-get install -y git
RUN apt-get clean

# After: Single layer
RUN apt-get update && \
    apt-get install -y curl git && \
    apt-get clean && \
    rm -rf /var/lib/apt/lists/*

Step 6: Use .dockerignore

Create .dockerignore:

node_modules
npm-debug.log
.git
.gitignore
README.md
.env
.DS_Store
*.md
.vscode
.idea
dist
build
coverage