This directory includes scripts and tools for setting up Flutter's continuous integration environments.
Flutter's Linux tasks run on a custom Docker image. The Dockerfile for this image can be found at /dev/ci/docker_linux/Dockerfile. On each new change to this Dockerfile, Cirrus will build a new version of the Docker image as a dependency to any Linux tests. It is no longer necessary to manually build and push the Docker image locally.
There are some factors external to the actual Dockerfile that would necessitate rebuilding the Docker image, such as upstream code changes, (Linux distribution) repository updates or a file that gets COPYied into the image changing. In this case, a trivial Dockerfile change (such as a comment) would invalidate the cache and trigger a rebuild.