Docker hands-on
2 likes743 views
This document provides an overview of Docker terminology and hands-on Docker activities. It defines that layers in Docker are read-only file systems that images are built from, with images never changing. A Dockerfile automates building images by containing build commands. Hands-on steps demonstrate creating a container, committing it to an image, and using a Dockerfile to build an image running a Django app. The document also briefly explains using nsenter to debug containers.
Docker hands-on
- 3. Agenda Talk ➔ Understanding the Docker terminology ➔ What is a layer? ➔ What are Docker images? Hands-on ➔ Creating a container ➔ Creating a docker image ➔ Dockerfile ➔ Using nsenter
- 4. What is a Layer? ➔ In traditional Linux, kernel mounts the root file system as read-only and later switches to read-write mode ➔ When Docker mounts the root, it starts read-only ➔ Later, instead of turning to read-write mode, it adds read-write file system over the read-only file system ➔ There could be multiple read-only file systems stacked on top of each other ➔ Each of this file system is called as layer
- 5. What is a layer (contd..) ➔ Any time a process creates a file, this happens in top layer. ➔ If some file from lower layer needs to be updated, it first gets copied to top layer. ➔ Changes go into the copy ➔ Version of file on lower layer remains unchanged but cannot be seen by applications ➔ Union File System - union of read-write and all read-only layers
- 6. What is a Layer? (contd.)
- 7. What are Docker images? ➔ In Docker, a read-only layer is called in Image ➔ An image never changes ➔ Each image depends on one more image which forms the layer beneath it ➔ This lower image is sometimes referred to as Parent Image ➔ An image that has no parent image is called Base Image
- 8. What are Docker images? (contd.)
- 9. What are Docker images? (contd.)
- 10. Creating a container $ sudo docker pull ubuntu:14.10 $ sudo docker run -ti ubuntu:14.10 /bin/bash $ ip a $ hostname $ uname -a
- 11. Creating an image ➔ We will create a minimal image from the container we created in previous step $ sudo docker ps $ sudo docker ps -a $ man docker-commit $ sudo docker commit <container-id> -t <repository>/<tag> $ sudo docker tag <image> <tag>
- 12. What is a Dockerfile? ➔ Automates building images ➔ A text document that contains commands to build an image ➔ Parsed by command docker buildto start image creation process ➔ Clone below repo: $ git clone https://github.com/dharmit/docker_ahmedabad_meetup_2/ ➔ Examine the Dockerfile
- 13. What is a Dockerfile? (contd..) ➔ FROM python:3.4 ➔ WORKDIR /code ➔ ADD django_code /code ➔ RUN pip3 install -r requirements.txt ➔ CMD python3 manage.py runserver 0.0.0.0:8000
- 14. Let’s build! ➔ $ sudo docker build -t docker_ahmedabad . ➔ $ sudo docker images ➔ $ sudo docker run -d -p 80:8000 docker_ahmedabad ➔ $ sudo docker ps ➔ In the browser, navigate to 127.0.0.1
- 15. If it didn’t work for you
- 16. nsenter ➔ Data backup ➔ Check logs ➔ Restart a service ➔ Edit configuration ➔ Debugging SSH
- 17. nsenter (contd..) ➔ Provided by your distro’s util-linux package ➔ How to use it: $ PID=$(sudo docker inspect --format {{.State.Pid}} <container_name_or_ID>) $ nsenter --target $PID --mount --uts --ipc --net --pid /bin/bash ➔ Specify /bin/bash if you’re using a different shell
- 18. Image and content credits ➔ http://docker.com ➔ http://redhat.com ➔ http://auberginesolutions.com
- 19. Questions?