anchor.diff:  
   [source]
   ----
  -8-jdk: Pulling from library/openjdk
  +openjdk:8-jdk: Pulling from library/openjdk
   
   386a066cd84a: Already exists
   75ea84187083: Already exists
  
positive.code: # Docker starter kit part 2: Anatomy of an Image and a Container, data management
  
  In the https://pierrebtz.github.io/2016/11/27/Docker-starter-kit-part-1-Getting-Started-Containers-lifecycle.html[first part] of this blog series on Docker, you had the opportunity to follow a Docker basic tutorial and to have an overview of the lifecycle of a Docker container.
  
  In this post, we will have an overview on what makes a Docker image and a container.
  Then we will check how we can manage data with Docker.
  We will then finish by an hands on to see an interesting usage of what we saw.
  
  ## Anatomy of an image
  
  
negative.code: 
  [quote, Docker Official Documentation]
  Union file systems, or UnionFS, are file systems that operate by creating layers, making them very lightweight and fast. Docker uses union file systems to provide the building blocks for containers.
  
  We will see next how those UnionFS are exploited in Docker.
  
  ### UnionFS and Docker Images
  
  A Docker image is made of several layers.
  Each layer represents a filesystem difference with the layer below it.
  The stack of all the layers makes up the filesystem of an image.
  Each layer is *read only* and shared between the images (and the containers, as we will see in the next part).
  
  As you may have guessed, all of this means that you need to be very careful when building new image to maximize the reuse of layers.
  We will discuss this in details in another blog post of this series.
  
  ### Hands On!
  
  Let us take a concrete example.
  Let us pull a maven image:
  