Images

• You cannot sum the size of the images to understand the total amount of space that docker is using - docker is even more space efficient than the listed number (usually)

Tags (Versioning)

We can have the same image with multiple TAGS by specifying a tag (which is usually a version) when committing. Say we have a container with the ID af407c0ef7c8 that we would like to create an image from. We can do this with docker commit:

$ docker commit af407c0ef7c8 myimage

This has created an image myimage from the container af407c0ef7c8. But what if the app from the container has changed, but we dont want to rename the next image entirely? Surely, theres a way to retain the myimage name but only change the tag. We can do this by:

$ docker commit af407c0ef7c8:v2.1 myimage

Now, when we run docker images we’ll have:

REPOSITORY          TAG                 IMAGE ID            CREATED             SIZE
myimage             v2.0                1442b904b529        3 seconds ago       223MB
myimage             latest              e0381948613c        12 seconds ago      223MB

So we see that both images have the name myimage, but with different tags. We can access these images by:

Removing Images

Docker images can accumulate quickly, and take up a lot of space. The docker command docker rmi image:tag removes the image image with tag tag.

Building Images (Dockerfiles)

Dockerfiles are small programs which describe to docker how to build an image.

$ docker build -t <DESIRED-NAME> .

In this example, the current directory ./ is the location of the dockerfile. Each line of a dockerfile takes in the state of the previous image and creates a new one - it does not delete the existing image. Thus, each step of running a dockerfile is cached. If the dockerfile is unchanged and a container has already been created, the