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Add a best practice to reduce cache invalidations 

inspired by https://github.com/docker-training/docker-fundamentals/pull/206

Signed-off-by: Sven Dowideit <SvenDowideit@home.org.au>
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Sven Dowideit 2014-10-08 11:23:54 +10:00 committed by Sven Dowideit
parent c2428ff865
commit a36ba19cca
1 changed files with 15 additions and 1 deletions
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16
docs/sources/articles/dockerfile_best-practices.md
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@ -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: