What are repository and tags? Why do they a

问题:

This is what docker images shows before I run docker build.

$ docker images
REPOSITORY          TAG                 IMAGE ID            CREATED             VIRTUAL SIZE
myapp               latest              a38da0bd9e0b        6 seconds ago       523.8 MB
golang              onbuild             b4997c557048        10 days ago         517.2 MB

After I make some changes to the myapp source code, I run docker build -t myapp . and I end up with images named <none>.

$ docker images
REPOSITORY          TAG                 IMAGE ID            CREATED                      VIRTUAL SIZE
myapp               latest              a38da0bd9e0b        Less than a second ago ago   523.8 MB
<none>              <none>              e4209f97e819        10 minutes ago               523.8 MB
golang              onbuild             b4997c557048        10 days ago                  517.2 MB

I know I can remove them with docker rmi <IMAGE ID>, but why does that happen in the first place? How can I prevent that from happening? The Dockerfile I'm building looks like this.

FROM golang:onbuild
EXPOSE 8080

回答1:

If you reassign a tag or image name to another image, your image will lose its tag or name. It's really that simple. Your myapp repo image tagged latest with ID a38da0bd9e0b used to be named and tagged on image ID e4209f97e819.