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I know that an image consists of many layers. for example, if u run "docker history [Image]", u can get a sequence of ids, and the ID on the top is the same as the image id, the rest IDs are layer ID.
in this case, are these rest layer IDs correspond to some other images? if it is true, can I view a layer as an image?
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Layers are what compose the file system for both Docker images and Docker containers. It is thanks to layers that when you pull a image, you eventually don't have to download all of its filesystem. If you already have another image that has some of the layers of the image you pull, only the missing layers are actually downloaded.
Docker Image is an executable package of software that includes everything needed to run an application. This image informs how a container should instantiate, determining which software components will run and how. Docker Container is a virtual environment that bundles application code with all the dependencies required to run the application.
A Docker image consists of several layers. Each layer corresponds to certain instructions in your Dockerfile. The following instructions create a layer: RUN, COPY, ADD. The other instructions will create intermediate layers and do not influence the size of your image. Let’s take a look at an example.
The Dockerfile instructions that modiy the image filesystem namely are ADD, COPY and RUN. Furthermore, a Docker image merely is a configuration object stored in JSON format. Such a JSON object contains, besides to image metadata like the CMD instruction, an ordered list of layers. Running docker image inspect will print those layers.
Layers are what compose the file system for both Docker images and Docker containers.
It is thanks to layers that when you pull a image, you eventually don't have to download all of its filesystem. If you already have another image that has some of the layers of the image you pull, only the missing layers are actually downloaded.
are these rest layer IDs correspond to some other images?
yes, they are just like images, but without any tag to identify them.
can I view a layer as an image?
yes
docker pull busybox
docker history busybox
IMAGE CREATED CREATED BY SIZE COMMENT d7057cb02084 39 hours ago /bin/sh -c #(nop) CMD ["sh"] 0 B cfa753dfea5e 39 hours ago /bin/sh -c #(nop) ADD file:6cccb5f0a3b3947116 1.096 MB
Now create a new container from layer cfa753dfea5e as if it was an image:
docker run -it cfa753dfea5e sh -c "ls /"
bin dev etc home proc root sys tmp usr var
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