Learning Docker - Second Edition

The FROM instruction

The FROM instruction is the most important one and is the first valid instruction of a Dockerfile. It sets the base image for the build process. Subsequent instructions will use this base image and build on top of it. The Docker build system lets you flexibly use the images built by anyone. You can also extend them by adding more precise and practical features. By default, the Docker build system looks for the images in the Docker host. However, if the image is not found in the Docker host, then the Docker build system will pull the image from the publicly available Docker Hub Registry. The Docker build system will return an error if it cannot find the specified image in the Docker host and the Docker Hub Registry.