Remove usage of the VOLUME instruction

[polarathene]

The VOLUME instruction should be removed from the image build.

• Containers already persist state internally until the container is destroyed (for example, an image upgraded to a new tag).
• Proper persistence externally should be explicit.

docker-library-redis/debian/Dockerfile

Lines 160 to 162 in 7109557

	RUN mkdir /data && chown redis:redis /data
	VOLUME /data
	WORKDIR /data

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Anonymous volumes are created when an image has a VOLUME instruction. They will initialize by copying any of the existing content at the mount point (unlike a bind mount volume which typically replaces content at the mount point):

• With docker run --rm ..., each container instance started will create a new anonymous volume. Without the --rm, these will accumulate pointlessly while the user may not be aware of this implicit waste on their system.
• Docker Compose behaves differently, with additional logic to preserve the same anonymous volume across instances of the container for a given compose project.

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The VOLUME instruction provides no value to an image. It only causes problems.

For detailed justification, please see below context for my previous write-up on this subject:

• fix: Dockerfile - VOLUME directive is an anti-pattern kanidm/kanidm#2948
• Dockerfile: Remove VOLUME instruction ory/hydra#3683
• Remove VOLUME instructions caddyserver/caddy-docker#118 (comment)
• Example of implicit 2GB disk usage per container instance (not applicable to images with empty VOLUME published, but clearly documents a VOLUME concern)

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Additional context (docker-library specific)

This issue is being raised across docker-library repos (with the only change the Dockerfile referenced snippet to change). It is similar to the past (stale?) docker-library issues for mongo, postgres, mysql, redis.

It is unclear why those older related issues on this topic have remained open for 6-8 years instead of resolving them. If a maintainer could clarify any pragmatic reason to keep VOLUME as a blocker, that would be appreciated. So far the only reason I recall is with Docker Compose, but that seems like a weak argument when persistence actually matters it should be explicit.

If the length (plus varying discussion chains) and age of those issues contribute to the lack of resolution, the issue I raise here hopefully condenses justification for removal into a consistent an easier to digest manner to drive this change forward.

As these are images maintained officially under the docker-library umbrella, it would help endorse VOLUME as an anti-pattern instead of encourage it's usage.