update best practices #22169
update best practices #22169
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| something like `wget` and `tar`, because it ensures a more precise build cache. | ||
| `ADD` also has built-in support for checksum validation of the remote | ||
| resources, and a protocol for parsing branches, tags, and subdirectories from | ||
| [Git URLs](/reference/cli/docker/buildx/build.md#git-repositories). | ||
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| > [!NOTE] | ||
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| > `ADD` redownloads the file every time the image is built to verify the checksum |
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This is not correct for servers that support etags. Only HEAD request is needed to know the file has not changed if there is local cache.
| If the file being downloaded is supposed to be part of the image and is okay to be redownloaded on each build (to verify changes), using `ADD` as part of the image build is more suitable. | ||
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| If the file is an archive being extracted, or not supposed to be part of the final image, using `ADD` by itself would add an additional layer and subsequently removing it using `RUN rm` will not decrease the image size. In this case, look at the below example to use a multi stage build with a `scratch` image to download the file using `ADD` and bind mounting it where needed in the final image. |
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I don't see how "supposed to be part of final image" matters in here. Layers in the target stage end up in the exported image, and RUN rm does not release data from the parent layers. This is true for all instructions and nothing specific about ADD or RUN.
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It was to clarify that always using ADD in your image build process is not the recommendation, since it adds a layer when you might not want one, which is how saying ADD is always better than curl/wget in the best practice reads to me. Is there a better way to phrase that using ADD without a multi stage build to bring it in when the artifact is not needed in the final image is not a best practice?
Description
Update the
ADDrecommendation to be clear on the behavior overRUN curland counterparts.Related issues or tickets
Closes #22168
Related to #18582
Reviews
Initially changed as a result of discussion in moby/buildkit#4125