Docker was built to make sure that code can run on any device without any issues of missing libraries, wrong versions, etc.

However if you use the "latest" tag instead of a fixed version number, then you actually don't know on beforehand with which version of the image you'll end up. Perhaps your code is at the time of writing compatible with the "latest" version but not in the future. Is it then a bad practice to use this tag? Is it a better practice to use a fixed version number?

CodePudding user response：

Usually, probably, for the reasons you state, you likely want to avoid ...:latest tags here.

For databases in particular, there can be differences in the binary interfaces, and there definitely are differences in the on-disk storage. If you were expecting MySQL 5.7 but actually got MySQL 8.0 you might get some surprising behavior. If a MySQL 9.0 comes out and you get an automatic upgrade then your local installation might break.

A generic reason to avoid ...:latest is that Docker will use a local copy of an image with the right tag, without checking Docker Hub or another repository. So again in the hypothetical case where MySQL 9.0 comes out, but system A has an old mysql:latest that's actually 8.0, docker run mysql on an otherwise clean system B will get a different image, and that inconsistency can be problematic.

You will probably find Docker image tags for every specific patch release of the database, but in general only the most recent build gets security updates. I'd suggest that pinning to a minor version mysql:8.0 is a good generic approach; you may want the more specific version mysql:8.0.29 in your production environment if you need to be extremely conscious of the upgrades.

Some other software is less picky this way. I'd point at the Redis in-memory data store and the Nginx HTTP server as two things where their network interfaces and configuration have remained very stable. Probably nothing will go wrong if you use nginx:latest or redis:latest, even if different systems do wind up with different versions of the image.