Dockerfile Best Practices

Question

What is the difference between a Docker image and a container? What are some Dockerfile best practices?

Answer

An image is a read-only template containing the application and dependencies. A container is a running instance of an image. Best practices include: use official base images, minimize layers by combining RUN commands, use multi-stage builds to reduce image size, don't run as root, use specific version tags instead of latest, and order instructions from least to most frequently changing to leverage layer caching.

Why This Matters

Container optimization directly impacts deployment speed, security, and costs. Smaller images deploy faster, have fewer vulnerabilities, and cost less to store. Understanding these concepts helps DevOps engineers build efficient CI/CD pipelines.

Code Examples

Optimized multi-stage Dockerfile

dockerfile

Common Mistakes

Using 'latest' tag in production
Running containers as root
Not using .dockerignore to exclude unnecessary files

Follow-up Questions

Interviewers often ask these as follow-up questions

What is the difference between COPY and ADD?
How does layer caching work in Docker builds?
What is the difference between CMD and ENTRYPOINT?