How Docker Works

• Linux Container is used to isolate processes. This process isolation will contain all the code, dependencies, binaries and settings required to run the process.
• Docker containers when they started used to create linux containers. Linux releases where impacting docker containers, so they have written their own container creation library (runc)
• Refer Here for understanding docker internals
• Inside the container (process isolations), it has its own process tree and it has its own filesystem.
• CPU and memory are also allocated to the container
• This isolated process has its own ip address
• Container is getting whatever is needed to run the application. But How?
  • Namespaces
  • CGroups
• Process Isolation: Each container runs with its own kernel namespaces for the following
  • Processes
  • Networks
  • Users
  • Mount
  • IPC
  • UTS

Docker Image

• First Responsibility of DevOps Engineer: Containerize your applications. This means creating docker images for your applications.
• Docker image is collection of layers.
• Lets build a docker image for an application gameoflife
  • Installation:
    • tomcat with Java 8 installed
    • copy the gameoflife.war file into webapps folder of tomcat
  • To make this work we have taken an existing image with java and tomcat installed and copied our package into the folder and then application started working
  • Doing this on running container is not sensible, it would be better if we can have some way of creating images.
  • Steps:
    • Take existing image
    • Copy the necessary files/configurations
    • Create an image with this.
• To Create images docker has Dockerfile , we will be using that from our next class. Refer Here for docker file reference.