Too Long; Didn't Read
Dockerfile developers copy files and directories from the host machine into the Docker image during image build. The COPY instruction is "the same as ADD, but without the tar and URL handling" COPY can extract and copy local tar archives and it can also download files from URLs. The best practice is to use a COPY instead of ADD to unpack local archives and download URLs. If Docker does not recognize the archive format during the build, it will copy the archive as it is into the image without warning.