10 Essential Docker Image Best Practices Every DevOps Engineer Should Follow

Docker image best practices are essential for building efficient, secure, and maintainable containerized applications. Whether you’re preparing for DevOps interviews or optimizing production deployments, understanding how to create optimized Docker images demonstrates professional-level container expertise.

This is a frequently asked Docker and DevOps interview question that tests your understanding of container optimization, security, and operational best practices. Interviewers want to see if you know how to build production-grade images, not just images that work.

What Interviewers Are Really Looking For

When asked about docker image best practices, interviewers want to assess:

• Your understanding of multi-stage builds and layer optimization
• Knowledge of security scanning and vulnerability management
• Experience with minimal base images and image size reduction
• Familiarity with caching strategies and build performance
• Understanding of metadata, labels, and image documentation
• Practical experience with production deployment considerations

Your answer should demonstrate that you think beyond just getting containers to run—you understand how to build images that are secure, efficient, and maintainable at scale.

Core Docker Image Best Practices Principles

Docker image best practices revolve around creating images that are small, secure, fast to build, and easy to maintain. Following docker image best practices correctly ensures your containers perform well in production environments.

Key principles include:

• Minimize image size: Smaller images deploy faster and reduce attack surface
• Optimize layer caching: Proper layer ordering speeds up builds dramatically
• Security first: Scan for vulnerabilities and use minimal base images
• Reproducible builds: Pin versions and use specific tags, never :latest
• Clear documentation: Use labels and maintain comprehensive documentation

Essential Docker Image Best Practices

1. Use Multi-Stage Builds

Multi-stage builds are fundamental to docker image best practices, allowing you to separate build dependencies from runtime requirements.

Implementation approach:

dockerfile

# Build stage
FROM node:18-alpine AS builder
WORKDIR /app
COPY package*.json ./
RUN npm ci --only=production
COPY . .
RUN npm run build

# Production stage
FROM node:18-alpine
WORKDIR /app
COPY --from=builder /app/dist ./dist
COPY --from=builder /app/node_modules ./node_modules
EXPOSE 3000
CMD ["node", "dist/index.js"]

Why this matters:

• Reduces final image size by 60-80%
• Excludes build tools and dev dependencies
• Separates concerns between build and runtime
• Improves security by minimizing attack surface

2. Choose Minimal Base Images

Selecting the right base image is critical for docker image best practices and overall security.

Base image comparison:

Base Image	Size	Use Case	Security
ubuntu:latest	~77 MB	Development, legacy apps	More vulnerabilities
alpine:latest	~5 MB	Production, microservices	Minimal attack surface
scratch	0 MB	Static binaries (Go, Rust)	Most secure
distroless	~2-20 MB	Production apps	Very secure, no shell

Best practice recommendation:

dockerfile

# For Node.js applications
FROM node:18-alpine

# For Go applications
FROM golang:1.21-alpine AS builder
# ... build steps ...
FROM scratch
COPY --from=builder /app/binary /binary

Why Alpine and distroless:

• 95% smaller than full Ubuntu images
• Fewer packages means fewer vulnerabilities
• Faster download and deployment times
• Lower storage and bandwidth costs

3. Optimize Layer Caching

Understanding Docker’s layer caching is essential for docker image best practices and build performance.

Inefficient approach (rebuilds frequently):

dockerfile

FROM node:18-alpine
WORKDIR /app
COPY . .                    # Changes frequently, invalidates cache
RUN npm install             # Reinstalls everything every time
CMD ["npm", "start"]

Optimized approach (leverages caching):

dockerfile

FROM node:18-alpine
WORKDIR /app

# Copy dependency files first (change infrequently)
COPY package*.json ./
RUN npm ci --only=production

# Copy application code last (changes frequently)
COPY . .

CMD ["npm", "start"]

Why ordering matters:

• Docker caches each layer independently
• Layers are reused if nothing below them changed
• Proper ordering can reduce build time from 5 minutes to 10 seconds
• Dependency installation is typically the slowest step

Key principle: Order Dockerfile instructions from least frequently changed to most frequently changed.

4. Minimize Layer Count and Size

Each RUN, COPY, and ADD instruction creates a new layer. Following docker image best practices means being strategic about layer creation.

Inefficient (creates unnecessary layers):

dockerfile

RUN apt-get update
RUN apt-get install -y curl
RUN apt-get install -y git
RUN apt-get clean

Optimized (combines related operations):

dockerfile

RUN apt-get update && \
    apt-get install -y --no-install-recommends \
        curl \
        git && \
    apt-get clean && \
    rm -rf /var/lib/apt/lists/*

Why this matters:

• Reduces final image size by cleaning up in the same layer
• Fewer layers means faster image pulls
• Each layer adds overhead to the image
• Cleanup in separate layers doesn’t reduce image size

5. Implement Security Scanning

Security scanning is non-negotiable in docker image best practices for production environments.

Tools for vulnerability scanning:

bash

# Using Docker Scout (built-in)
docker scout cves myapp:latest

# Using Trivy
trivy image myapp:latest

# Using Snyk
snyk container test myapp:latest

# Using Grype
grype myapp:latest

Integration into CI/CD:

yaml

# GitHub Actions example
- name: Scan Docker image
  uses: aquasecurity/trivy-action@master
  with:
    image-ref: 'myapp:${{ github.sha }}'
    severity: 'CRITICAL,HIGH'
    exit-code: '1'  # Fail build on vulnerabilities

Best practices for security:

• Scan images in CI/CD pipeline before deployment
• Fail builds on high/critical vulnerabilities
• Regularly update base images and dependencies
• Use vulnerability databases (CVE, NVD)
• Implement automated security updates

6. Use Specific Version Tags

Never rely on :latest or unpinned versions in production docker image best practices.

Bad practice (unpredictable):

dockerfile

FROM node:latest
RUN npm install express

Good practice (reproducible):

dockerfile

FROM node:18.19.0-alpine3.19
RUN npm install express@4.18.2

Why pinning matters:

• :latest tag changes over time, breaking reproducibility
• Different team members may build with different versions
• Production deployments should be deterministic
• Makes rollbacks and debugging easier
• Enables gradual, controlled upgrades

Version pinning strategy:

• Base images: Pin to specific version + OS version
• Dependencies: Use lockfiles (package-lock.json, Pipfile.lock, go.sum)
• System packages: Pin major versions where possible

7. Run as Non-Root User

Running containers as root violates fundamental docker image best practices for security.

Insecure (runs as root):

dockerfile

FROM node:18-alpine
WORKDIR /app
COPY . .
CMD ["node", "server.js"]  # Runs as root

Secure (runs as non-root user):

dockerfile

FROM node:18-alpine

# Create app user
RUN addgroup -g 1001 -S nodejs && \
    adduser -S nodejs -u 1001

WORKDIR /app

# Copy files and set ownership
COPY --chown=nodejs:nodejs . .

# Switch to non-root user
USER nodejs

CMD ["node", "server.js"]
```

**Why non-root matters:**
- Limits damage if container is compromised
- Prevents privilege escalation attacks
- Follows principle of least privilege
- Required by many Kubernetes security policies
- Industry standard for production deployments

### 8. Leverage .dockerignore

The `.dockerignore` file is essential for docker image best practices and build performance.

**Create `.dockerignore`:**
```
# Dependencies
node_modules
npm-debug.log

# Build outputs
dist
build
*.log

# Development files
.git
.gitignore
.env
.env.local
*.md
Dockerfile*
docker-compose*.yml

# IDE files
.vscode
.idea
*.swp

# Test files
coverage
test
*.test.js
*.spec.js

# CI/CD
.github
.gitlab-ci.yml

Why .dockerignore is critical:

• Reduces build context size (can save gigabytes)
• Speeds up docker build by 50-90%
• Prevents accidentally copying secrets or credentials
• Keeps images smaller by excluding unnecessary files
• Similar to .gitignore but for Docker builds

9. Add Metadata with Labels

Labels provide essential documentation and are part of docker image best practices for maintainability.

Comprehensive labeling:

dockerfile

FROM node:18-alpine

LABEL org.opencontainers.image.title="My Application"
LABEL org.opencontainers.image.description="Production API service"
LABEL org.opencontainers.image.version="1.2.3"
LABEL org.opencontainers.image.authors="devops@company.com"
LABEL org.opencontainers.image.source="https://github.com/company/repo"
LABEL org.opencontainers.image.licenses="MIT"
LABEL maintainer="DevOps Team <devops@company.com>"

# Custom labels for your organization
LABEL com.company.team="platform"
LABEL com.company.environment="production"

Why labels matter:

• Enables image discovery and inventory management
• Provides version tracking and audit trails
• Supports automated tooling and dashboards
• Documents ownership and contact information
• Follows OCI (Open Container Initiative) standards

10. Optimize for Production

Production-ready docker image best practices include health checks, proper signal handling, and resource awareness.

Production-optimized Dockerfile:

dockerfile

FROM node:18-alpine

# Install dumb-init for proper signal handling
RUN apk add --no-cache dumb-init

# Create non-root user
RUN addgroup -g 1001 -S nodejs && \
    adduser -S nodejs -u 1001

WORKDIR /app

# Copy dependencies first
COPY --chown=nodejs:nodejs package*.json ./
RUN npm ci --only=production && npm cache clean --force

# Copy application
COPY --chown=nodejs:nodejs . .

USER nodejs

# Health check
HEALTHCHECK --interval=30s --timeout=3s --start-period=5s --retries=3 \
  CMD node healthcheck.js

EXPOSE 3000

# Use dumb-init to handle signals properly
ENTRYPOINT ["dumb-init", "--"]
CMD ["node", "server.js"]

Production considerations:

• Health checks: Enable Kubernetes/ECS to detect unhealthy containers
• Signal handling: Proper SIGTERM handling for graceful shutdowns
• Resource limits: Set memory and CPU limits in deployment manifests
• Logging: Log to stdout/stderr, never to files inside containers
• Configuration: Use environment variables, never hardcode configs

Docker Image Best Practices Comparison

Practice	Development	Production
Base Image	ubuntu, python	alpine, distroless
Caching	Less critical	Highly optimized
Security Scanning	Optional	Required in CI/CD
Version Pinning	:latest acceptable	Always pin versions
Multi-stage Builds	Optional	Strongly recommended
User	Root acceptable	Always non-root
Layer Count	Less important	Minimized
Health Checks	Optional	Required
Labels	Basic	Comprehensive
.dockerignore	Basic	Comprehensive

Advanced Docker Image Best Practices

Build Arguments vs Environment Variables

Understanding when to use ARG vs ENV is important for docker image best practices.

dockerfile

# ARG: Available only during build
ARG NODE_VERSION=18
FROM node:${NODE_VERSION}-alpine

# ENV: Available during build AND runtime
ENV NODE_ENV=production
ENV APP_PORT=3000

# Best practice: Use ARG for build-time values, ENV for runtime

Caching Strategies for Package Managers

Different package managers require different docker image best practices for optimal caching.

Python with pip:

dockerfile

COPY requirements.txt .
RUN pip install --no-cache-dir -r requirements.txt
COPY . .

Go with modules:

dockerfile

COPY go.mod go.sum ./
RUN go mod download
COPY . .

Node.js with npm:

dockerfile

COPY package*.json ./
RUN npm ci --only=production
COPY . .

Scanning and Fixing Vulnerabilities

Implementing docker image best practices includes continuous vulnerability management.

Automated vulnerability remediation workflow:

1. Scan image: docker scout cves myapp:latest
2. Review findings: Identify high/critical vulnerabilities
3. Update base image: Use newer patch version
4. Update dependencies: Upgrade vulnerable packages
5. Rebuild and rescan: Verify vulnerabilities are resolved
6. Deploy updated image: Push to registry and deploy

Common Mistakes to Avoid

🚫 Using :latest tag: Always pin specific versions for reproducibility

🚫 Running as root user: Security risk, violates least privilege principle

🚫 No .dockerignore file: Bloats images and slows builds significantly

🚫 Installing unnecessary packages: Increases size and attack surface

🚫 Not using multi-stage builds: Results in massive production images

🚫 Ignoring layer caching: Leads to slow, inefficient builds

🚫 No security scanning: Deploys vulnerable images to production

🚫 Copying entire project first: Invalidates cache on every code change

Each of these mistakes demonstrates lack of production experience with containers.

How This Connects to Infrastructure as Code

Once you’ve mastered docker image best practices, you’ll deploy these containers using orchestration platforms like Kubernetes or ECS. Understanding how to structure a Terraform project helps you manage container infrastructure consistently.

For team collaboration, you’ll want to understand Terraform Cloud vs local Terraform for managing container deployments across environments.

When designing your infrastructure, consider AWS high availability architecture principles to ensure your containerized applications remain resilient.

Example Interview Answer

Here’s how to confidently answer “What docker image best practices do you follow?” in an interview:

“I follow several critical docker image best practices for production deployments.

First, multi-stage builds: I separate build dependencies from runtime requirements, typically reducing image size by 70%. For a Node.js app, I build in one stage and copy only production artifacts to the final stage.

Second, minimal base images: I use Alpine Linux or distroless images instead of full Ubuntu, reducing size from 500MB to under 50MB and minimizing vulnerabilities.

Third, layer optimization: I copy package manifests before application code so dependency installation is cached. This reduces build time from 5 minutes to under 30 seconds for typical code changes.

Fourth, security: I scan images with Trivy or Docker Scout in CI/CD, run containers as non-root users, and pin all versions for reproducibility.

Fifth, production readiness: I include health checks, use dumb-init for proper signal handling, and add comprehensive labels for tracking.

I also maintain a comprehensive .dockerignore file and combine RUN commands to minimize layer count. These practices ensure our images are secure, efficient, and production-ready.”

This answer demonstrates both breadth of knowledge and practical implementation experience.

Docker Image Best Practices Checklist

Build Time

• Use multi-stage builds to separate build and runtime
• Choose minimal base images (Alpine, distroless, scratch)
• Pin specific version tags, never use :latest
• Order Dockerfile instructions for optimal caching
• Combine RUN commands to minimize layers
• Use comprehensive .dockerignore file
• Add metadata with LABEL instructions

Security

• Scan images for vulnerabilities in CI/CD
• Run containers as non-root user
• Minimize installed packages and dependencies
• Update base images and dependencies regularly
• Never include secrets or credentials in images
• Use specific package versions, not ranges

Production

• Add HEALTHCHECK instruction
• Use proper init system (dumb-init, tini)
• Log to stdout/stderr, not files
• Use environment variables for configuration
• Set resource limits in orchestration platform
• Test images before production deployment

Maintenance

• Document image purpose and usage
• Tag images with version and git SHA
• Maintain consistent Dockerfile patterns across projects
• Review and update images quarterly
• Monitor image registry for outdated images

Key Takeaways

• Docker image best practices start with multi-stage builds to dramatically reduce size
• Use minimal base images like Alpine or distroless for security and efficiency
• Optimize layer caching by ordering Dockerfile instructions strategically
• Security scanning is mandatory for production deployments
• Always run as non-root user to follow least privilege principle
• Pin all versions for reproducible, deterministic builds
• Add comprehensive labels for tracking and documentation
• Test docker image best practices in CI/CD before production deployment

Additional Resources

For official Docker guidance, review:

• Docker Best Practices for Writing Dockerfiles
• Docker Security Best Practices
• Multi-stage Build Documentation

This comprehensive approach to docker image best practices will help you confidently answer interview questions and build production-grade containers.