When a new version of Python (or a new version of Debian) is released, the :latest tag will point at the newer image. So which version of Python did you get? And which base operating system? In this case, the :latest tag currently points at version 3 of a container with Debian 9 installed. We cover this more in the Running Containers chapters in the book. Good or bad, this is the default behavior in Docker. Note that you didn’t specify the :latest tag, but that is what you got. The output you may see is Unable to find image 'python:latest' locally. If you have Docker installed run something like docker run python. The exact sha256 digest of an image (for example, look a bit at each option, and discuss why you may want to use one tagging strategy over another.Specify a tagged version number (for example, python:3, or python:3.7, or python:3.7.3).None (just use :latest, for example, just FROM python).When writing your own applications, you will need to decide which version of the base image(s) you will use in the FROM statement(s) of your Dockerfile(s). Currently that happens to be 3.7.3, but tomorrow that could be 3.7.4 if a new version is released. In a similar way, the python:3.7 image would be the latest available security patch of Python 3.7. Whenever 3.9 is released, that tag will get updated and the python:3 image will then contain version 3.9 instead. Today the python:3 container image specifically uses Python version 3.8. Some use a different base operating system images (Alpine VS Debian VS “slimmed-down” Debian), and they also indicate the specific versions of whatever language is installed in the image. Each of these tags represents different variations of an install of Python. Most of the popular languages use a similar tagging pattern in their official images on Docker Hub. There are several other version tags of python also available, such as: The name of the container is python, and 3 is the version tag. For example, the container python:3 is a container hosted on Docker Hub at. We’ll also explore some different strategies you will want to consider when using image version tags in your own Dockerfiles.ĭocker container names are split into 2 parts: the name of the container image, and the version tag of the container image. In this post we're going to talk about how versioning works in Docker container images. Other authors use latest for their development builds, while some won't publish a latest tag at all.This is a guest post by Justin Domingus, co-author with John of the Cloud Native DevOps with Kubernetes book. This imbues the tag with extra importance that Docker didn't intend. Many image creators do tag their newest releases with latest. This creates a lot of confusion within the Docker ecosystem. If you wanted my-image:v1 to also become the latest image, you'd need to manually tag and push it in a separate operation. The v1 tag is completely independent of latest, so building the third image has no effect on the existing two. If you now ran docker run my-image:latest, you'd be using the second image to be built. Here's an example of the resulting problem: That's the only time it'll be used - it doesn't automatically refer to the newest image you've built. In reality, latest is used as the default tag when you haven't specified anything else. The semantics of the latest tag seem to suggest some special meaning beyond what actually exists.
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