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Pin versions in apt-get install.

Problematic code:

FROM busybox
RUN apt-get install python

Correct code:

FROM busybox
RUN apt-get install python=2.7.*

Rationale:

https://docs.docker.com/develop/develop-images/instructions/#apt-get

Version pinning forces the build to retrieve a particular version regardless of what’s in the cache. This technique can also reduce failures due to unanticipated changes in required packages.

Additionally, software like Renovatebot can be used to keep pinned dependencies up to date. See e.g. https://docs.renovatebot.com/modules/datasource/deb/#usage-example