Docker Images

#docker

Docker image is collection of filesystems in simple.
Docker images contains the ROOTFS (root file system), USERFS (user file system), APPFS (application file systems for OPENJDK,TOMCAT and CUSTOMAPPS).
ROOTFS and USERFS together called as basic layer of an image.
APPFS (for example: openjdk, tomcat, custom app) together called as application layer of an image.
to fine the storage driver used by docker server, run docker info and see the storage driver output.
overlay2 is one of the storage driver used in docker to store docker images.
overlay2 directory is located inside of DOCKER-ROOT directory, whenever we pull images from other repository (like docker hub), that image layers will be stored in overlay2 directory as image layer sub directories.
when we create docker runtime, all layers of that image will be merged as single layer and attached to container as single mount (MNT) file system.
whenever we make changes (like writing file/updating file), that changes will get updated in both merged layer and image layer.
Docker uses sha2-256bit algorithm for encryption of docker images.