12장. Building container images

When building an image with Docker or Podman, a directory is specified to become the build context. This is true for both manual Builds and Build triggers, because the Build that is created by Quay.io is not different than running docker build or podman build on your local machine.

Quay.io Build contexts are always specified in the subdirectory from the Build setup, and fallback to the root of the Build source if a directory is not specified.

When a build is triggered, Quay.io Build workers clone the Git repository to the worker machine, and then enter the Build context before conducting a Build.

For Builds based on .tar archives, Build workers extract the archive and enter the Build context. For example:

example
├── .git
├── Dockerfile
├── file
└── subdir
    └── Dockerfile

Imagine that the Extracted Build archive is the directory structure got a Github repository called example. If no subdirectory is specified in the Build trigger setup, or when manually starting the Build, the Build operates in the example directory.

If a subdirectory is specified in the Build trigger setup, for example, subdir, only the Dockerfile within it is visible to the Build. This means that you cannot use the ADD command in the Dockerfile to add file, because it is outside of the Build context.

Unlike Docker Hub, the Dockerfile is part of the Build context on Quay.io. As a result, it must not appear in the .dockerignore file.