Effectively immutable tags taken from mutable ones

[bjaglin]

I find it very inconvenient that once an image such as debian:jessie (which is by nature a mutable reference) gets updated, there is no way to refer to the previous version, at least not without doing some introspection & local tagging when some images based on the previous one are still around on some machine.

It's probably an anti-pattern to inherit from such a mutable tag, at least if repeatability is a requirement. For the use cases where an image requires a certain snapshot of an image which is not semantically tagged, couldn't we provide date-suffixed tags, such as jessie_20140723, the date being the time of generation of the image?

I am aware this would introduce complexity when maintaining images (that date would need to be manually bumped to trigger the rebuild, and the previous one would just be laying in the registry), but how does it currently work anyway when an image needs to be rebuilt, even though the Dockerfile itself didn't change?

See boot2docker/boot2docker#440 for a symptom of this problem. I had similar issue when pulling by accident ubuntu:precise, and realizing that the latest LTS release brought changes that broke the flow downstream (actually, in that case, there is actually a semantic versioning, ubuntu:12.04.4 so that would be the easy way out).

[tianon]

You can use debian:7.5, debian:7.6 etc too - the actual stable releases of Debian don't have nearly as much flow as the current jessie (or testing in general) or sid do, since they're literally the development testing grounds for the next version of the OS, so using "jessie" for anything that needs to be consistently stable and repeatable before the jessie freeze in Nov is definitely an antipattern in itself. :)