COPY are functionally similar
ADD has some features like local-only tar extraction and remote URL support
Consequently, the best use for
ADD is local tar file auto-extraction into the image, as in
ADD rootfs.tar.xz /.
COPY only supports the basic copying of local files into the container
With multiple steps in Dockerfile, that use different files from your context -->
COPY them individually, rather than all at once. This will ensure that each step’s build cache is only invalidated (forcing the step to be re-run) if the specifically required files change.
COPY requirements.txt /tmp/RUN pip install --requirement /tmp/requirements.txtCOPY . /tmp/
Results in fewer cache invalidations for the
RUN step, than if you put the
COPY . /tmp/ before it.
Because image size matters, using
ADD to fetch packages from remote URLs is strongly discouraged; you should use
wget instead. That way you can delete the files you no longer need after they’ve been extracted and you won’t have to add another layer in your image.
For example, you should avoid doing things like:
ADD http://example.com/big.tar.xz /usr/src/things/RUN tar -xJf /usr/src/things/big.tar.xz -C /usr/src/thingsRUN make -C /usr/src/things all
And instead, do something like ⭐️ :
RUN mkdir -p /usr/src/things \&& curl -SL http://example.com/big.tar.xz \| tar -xJC /usr/src/things \&& make -C /usr/src/things all
For other items (files, directories) that do not require
ADD’s tar auto-extraction capability
You should always use