Docker Legacy Builder

Docker Legacy Builder is the original build engine used in Docker before the introduction of BuildKit. It processes Dockerfiles to create Docker images by executing commands in a step-by-step manner, caching intermediate layers for efficiency. It was the default builder in Docker versions prior to 18.09 and is still available for backward compatibility.

Also known as: Docker Classic Builder, Docker Old Builder, Legacy Docker Build, Docker Build (pre-BuildKit), Dockerfile Builder

Why learn Docker Legacy Builder?

Developers should learn about Docker Legacy Builder when working with older Docker setups or maintaining legacy projects that rely on its specific behavior. It's useful for understanding Docker's evolution and troubleshooting build issues in environments where BuildKit is not enabled or compatible, such as certain CI/CD pipelines or older infrastructure.

Learning Resources

• docs: Docker Documentation: Legacy Builder
• tutorial: Docker Blog: Introducing BuildKit
• video: YouTube: Docker Build - Legacy vs BuildKit
• course: Pluralsight Course: Docker Deep Dive