If I delete a file in a later layer, does the image size decrease?

No! This is a massive gotcha. If you download a 1GB file in Layer 2, and then use `RUN rm file.zip` in Layer 3, the final image size is STILL 1GB. The deleted file is merely 'hidden' in the final Union File System, but the 1GB data still exists in the immutable Layer 2. You must download and delete the file in the exact same `RUN` command.

How can I force Docker to ignore the cache entirely?

Sometimes you need a fresh build (e.g., if you are running `apt-get update` and want the latest security patches). You can pass the `--no-cache` flag to the `docker build` command.

Does `WORKDIR` create a layer?

Yes. Almost every command in a Dockerfile creates a layer. While `WORKDIR` or `ENV` layers are tiny (a few bytes), it is generally good practice to chain `RUN` commands together using `&&` to minimize the total number of layers.

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Layer Optimization & Caching

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