Docker updating image along when dockerfile changes

Question

I'm playing with docker by creating a Dockerfile with some nodejs instructions. Right now, every time I make changes to the dockerfile I recreate the image by running sudo docker build -t nodejstest . in my project folder however, this creates a new image each time and swallows my ssd pretty soon.

Is there a way I can update an existing image when I change the dockerfile or I'm forced to create a new one each time I make changes to the file?

Sorry if it's a dumb question

Answer 1

Docker build support caching as long as there is no ADD instruction. If you are actively developing and changing files, only what is after the ADD will be rebuilt.

Since 0.6.2 (scheduled today), you can do docker build --rm . and it will remove the temporary containers. It will keep the images though.

In order to remove the orphan images, you can check them out with docker images, and perform a docker rmi <id> on one of them. As of now, there is an auto-prune and all untagged images (orphans, previous builds) will be removed.

Answer 2

According to this best practices guide if you keep the first lines of your dockerfile the same it'll also cache them and reuse the same images for future builds