![]() In the output, you'll see each of the running commands happen in a temporary container that we now keep instead of automatically deleting. Lets build the image with an extra flag to save the temporary containers: docker image build -rm=false. # and now this cleans up that downloaded source codeĮach of those dd commands outputs a 1M file to the disk. RUN dd if=/dev/zero bs=1024 count=1024 of=/data/two RUN dd if=/dev/zero bs=1024 count=1024 of=/data/one # imagine this is downloading source code Lets take a contrived example Dockerfile: FROM busybox Examining layers of your own build with docker diff They make the most sense to me with an example. Because layers are intermediate images, if you make a change to your Dockerfile, docker will rebuild only the layer that was changed and the ones after that. The concept of layers comes in handy at the time of building images. Then, we tell docker to run bundle exec puma (which boots up the rails server). We add another layer on top of our starting image, setting the environment variable RAILS_ENV with the ENV command. You can think of it as staging changes when you're using git: You add a file's change, then another one, then another one.Ĭonsider the following Dockerfile: FROM rails:onbuildįirst, we choose a starting image: rails:onbuild, which in turn has many layers. Every command you specify ( FROM, RUN, COPY, etc.) in your Dockerfile causes the previous image to change, thus creating a new layer. ![]() ![]() I might be late, but here's my 10 cents (complementing ashishjain's answer):īasically, a layer, or image layer is a change on an image, or an intermediate image. ![]()
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