04-Docker.md

Part IV: Docker

Objectives:

By the end of this module, the SRE will:

• Describe the directives from a sample dockerfile
• Explain layers and the docker cache
• Start a docker container that runs ubuntu linux
• Describe the following container concepts:
  • base image
  • single pid
  • CMD vs ENTRYPOINT
  • logs
  • volumes
  • layers and ordering
  • caching
  • build
  • push

Deliverables

Complete the project described below. Answer the questions, then schedule a time to meet with your mentor and discuss the what you've built.

Docker

1. Setup

• Install docker
• https://www.youtube.com/watch?v=JprTjTViaEA
• https://jonnylangefeld.github.io/learning/Docker/How%2Bto%2BDocker.html
• login to Fairwinds quay and dockerhub via the terminal
  • You will need to be given access to these accounts, reach out for help.
  • https://hub.docker.com/u/reactiveops/dashboard/
  • docker login
  • https://quay.io/organization/reactiveops
  • quay login information https://docs.quay.io/solution/getting-started.html

2. Create new Dockerfile from ubuntu:16.04

   • https://www.youtube.com/watch?v=6Er8MAvTWlI

3. run apt-get update and apt-get upgrade --yes on separate lines in the Dockerfile

4. Build the docker file.

   • docker build -t intro_to_docker .
   • How many steps were there?

5. Build again

   • Why doesn’t it take as long?
     • The ubuntu image is already downloaded and can be referred to by its id (5e8b97a2a082)
     • Docker cache!
       • ---> Using cache
       • ---> 1dcd45e300d7
     • Every layer checks the Docker cache
       • The docker cache are images that exist on the disk
       • http://kimh.github.io/blog/en/docker/gotchas-in-writing-dockerfile-en/

6. Use docker history <image> to see each step and its layer id

   • Count the number of lines by using | wc -l
   • docker history d57d088b85d1 | wc -l
   • 9 lines!

7. Replace the two lines with apt-get update && apt-get upgrade --yes and build again

   • How many steps were there?
   • What is &&?
   • Use wc -l here
   • Why were there fewer steps?

More with Docker

Start a docker container that runs ubuntu linux

• docker run -it <image_id> bash

1. Using the ADD and RUN directives, add one of the scripts from before to the image and build the image.

   • https://docs.docker.com/engine/reference/builder/
   • Does the first step get run again or is cache used?

2. Move the ADD directive so it is above the RUN directive and build the image

   • Is cached used this time?
   • Why not?

3. Use the CMD and ENTRYPOINT directives in turn the Dockerfile to make the script run by default

   • https://goinbigdata.com/docker-run-vs-cmd-vs-entrypoint/

4. Rewrite the Dockerfile using ADD and CMD to add the script and run the command.

• Create a container using your latest image docker run -it <image_id> bash
  • How is this different than docker run -it <image> bash?
  • Run the docker image as a daemon with sleep 3600 as the main process docker run -d <image_id> sleep 3600
  • exec into the running container and run ps -ef to view the running processes
  • docker exec -it <container_id> bash
    • What is the pid of the sleep process?
    • What happens if you kill that pid

Learning Resources:

• https://medium.com/@jessgreb01/digging-into-docker-layers-c22f948ed612
• https://blog.phusion.nl/2015/01/20/docker-and-the-pid-1-zombie-reaping-problem/
• https://hackernoon.com/my-process-became-pid-1-and-now-signals-behave-strangely-b05c52cc551c
• https://www.boynux.com/containers-fat-thin/
• https://rominirani.com/docker-tutorial-series-part-7-data-volumes-93073a1b5b72
• https://www.youtube.com/watch?v=VOK06Q4QqvE