Overview of how the ray images are built:
Images without a "-cpu" or "-gpu" tag are built on ubuntu/focal. They are just an alias for -cpu (e.g. ray:latest is the same as ray:latest-cpu).
ubuntu/focal
└── base-deps:cpu
└── ray-deps:cpu
└── ray:cpu
└── ray-ml:cpu
nvidia/cuda
└── base-deps:gpu
└── ray-deps:gpu
└── ray:gpu
└── ray-ml:gpu