|
|
@@ -261,9 +261,23 @@ some features (like local-only tar extraction and remote URL support) that are
|
|
|
not immediately obvious. Consequently, the best use for `ADD` is local tar file
|
|
|
auto-extraction into the image, as in `ADD rootfs.tar.xz /`.
|
|
|
|
|
|
+If you have multiple `Dockerfile` steps 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.
|
|
|
+
|
|
|
+For example:
|
|
|
+
|
|
|
+ COPY requirements.txt /tmp/
|
|
|
+ RUN pip install /tmp/requirements.txt
|
|
|
+ COPY . /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 `curl` or `wget` instead. That way you can
|
|
|
-delete the files you no longer need after they’ve been extracted and you won't
|
|
|
+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:
|
|
|
|
Fred Lifton