This document provides an overview of Docker for developers. It discusses why Docker is useful for building applications, including portability across machines, isolating dependencies, and creating development environments that match production. Benefits of Docker like lightweight containers, a unified build process with Dockerfiles, standardized images from Docker Hub, and fast container startup times are outlined. Some cons like only working on Linux and added complexity are noted. Using Docker with Vagrant for a portable development environment is presented. Key Docker CLI commands and Docker Compose for defining multi-container apps are covered. Tips for debugging running containers are provided.

1. Docker in everyday
development
What every dev should know.

2. Justyna Ilczuk,
Senior Software / DevOps Engineer
at
Speaker
A scalable backend that helps developers
build complex apps
with only front-end code.
http://www.syncano.com/

4. Docker - An open platform for distributed
applications for developers and sysadmins.
* Powered by Linux Containers.
Build, Ship and Run
Any App, Anywhere

5. Why?

6. Why?
Portability rocks!
App works on all machines (not only on mine!)

7. Why?
Isolate and version dependencies on both
language and OS level
- better than virtualenv (rvm)

8. Why?
Build Dev Environment than resembles
production environment
- avoid strange bugs from dev/prod mismatch

10. Why?
Installing dockerized services is trivial
- You need a Postgres in version 9.4? Or
redis, or Rabbitmq, Elastic Search?
Just pull an image and start a container.

11. Still not convinced?

12. Docker pros
Lightweight
● busybox - 2.433 MB
● debian - 85.01 MB
● nginx - 91.66 MB
● redis - 111.2 MB

13. Docker pros
Unified build process
Dockerfile
FROM debian:latest
RUN apt-get update && apt-get install tmux
CMD tmux
$ docker build -t my_image .

14. Docker pros
Docker image format, portability, hub
$ docker pull organization/image_name
$ docker run -it organization/image_name
command
$ docker push me/my_image

17. Docker pros
Fast, starting container in 0.2 s
$ time docker run --rm ubuntu /bin/echo hello world
hello world
docker run --rm ubuntu /bin/echo hello world 0,02s user 0,01s system 9% cpu
0,271 total

18. Docker pros - summing up
● lightweight containers
● unified build process (Dockerfile)
● standardized images (Docker hub)
● fast, starting container in 0.2 s
● combining containers together
● distributed apps, microservices

19. Docker cons
● works only on GNU/Linux (needs vagrant /
boot2docker)
● new tool to learn
● another layer of complexity & overhead -
vagrant + Docker vs developing natively on
your machine

20. Docker + Vagrant
Containers on VMs

21. Docker + Vagrant
● Works everywhere
● Possible to try new tech, new OSes
○ CoreOS
○ Kubernetes
○ Mesos
○ etcd
○ Consul
● Distributed apps on your laptop

22. https://www.flickr.com/photos/110382334@N05/11303036263

23. Tools
● Docker CLI
● Docker compose (aka fig)
● Good old make

24. Docker CLI - the most important command
Running containers
$ docker run --rm ubuntu echo “Hello docker”
$ docker run -d -p 8080:80 nginx
$ docker run -it -v `pwd`:/app -p 8000:8000
my_app

25. Docker CLI - checking state
Checking state of containers
$ docker ps
$ docker images
$ docker logs my_container
$ docker top my_container

26. Docker CLI
https://docs.docker.
com/reference/commandline/cli/
$ docker --help
$ man docker
37 commands (for everything and more)

27. https://www.flickr.com/photos/pasukaru76/9824401426/in/photolist-9DE7Wa-cd6Wxf-dLkpKN-bW4iP-6TfKoP-okpdNP-
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7iuh42-fMEpmV-pybGg-bF1XGL-6cyxFq-tauEV-7zWj8-eewWz-a24hkr-4EjNgb-o4yuXd-f4PmxD-9bCZC5-e69XkS-
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5256km-3NdDg2-6KipNW

28. Containers everywhere
$ docker rmi
$ docker rm

29. Time for a better tool
Docker Compose

30. Docker Compose
Compose is a tool for defining and running
complex applications with Docker.

31. Docker Compose
● Define your containers in simple yaml file.
● Compose container together.
● Manage group of containers with single tool.

32. Demo of Docker Compose

33. Docker Compose - config
docker-compose.yml
redis:
image: redis
volumes:
- /var/docker/redis:data
ports:
- "6379"
web:
build: .
ports:
- "80:8080"
links:
- redis:redis
volumes:
- .:/app
environment:
- VARIABLE=value

34. Docker Compose - config
redis:
image: redis
volumes:
- /var/docker/redis:data
ports:
- “6379”

35. Docker Compose - config
web:
build: .
ports:
- "8090:8080"
links:
- redis:redis
volumes:
- .:/app
environment:
- VARIABLE=value

36. Docker Compose - commands
$ docker-compose build
$ docker-compose up
$ docker-compose ps

37. Docker Compose
https://docs.docker.com/compose/
https://docs.docker.com/compose/yml/
https://github.com/docker/compose
Example:
http://www.syncano.com/configuring-running-
django-celery-docker-containers-pt-1/

38. All is rainbows and unicorns now,
right?

39. Compose - good for running
containers
But missing dependencies.

40. Updating images
● Developers Bob and Alice work on an App.
● They use docker-compose to run App
● Bob adds new feature that requires Dependency X to be
baked into Docker image
● He updates the requirements.txt file that is used in
Dockerfile and rebuilds his image

41. Updating images
● Cool feature is merged to trunk
● Alice pulls changes
● Alice starts docker-compose and app breaks, because
of missing dependency in the container

42. Technical of people problem?
Should Alice remember to run `docker-
compose build`, `docker-compose rm` and
`docker-compose up` after each pull?

43. Automate everything.
Use smart technologies.
Use Make.

44. Good ol’ Makefile
run : build
docker-compose up -d
build : .built
.built : requirements.txt Dockerfile
docker-compose build
touch .built
stop :
docker-compose stop
clean : stop
docker-compose rm
rm .built
test : .built
docker-compose run web ./run_tests.sh ${ARGS}
.PHONY : run build clean stop test

45. Good ol’ Makefile
run : build
docker-compose up -d
build : .built
.built : requirements.txt Dockerfile
docker-compose build
touch .built

46. Makefile
● Uses docker-compose
● Best for dependencies
● Self documenting

47. Other problems that you might
encounter

48. Ups… something went wrong.
Building image failed.
- it stops at layer that failed
- starts from the last correct layer (cache)

49. Ups… something went wrong.
App in containers behaves in a strange way:
Logs and errors
- logging to stdout
- logging to volumes
- logging straight to Centralized Logging
- logging to sentry

50. Ups… something went wrong.
https://github.com/slafs/sentry-docker <3

51. Ups… something went wrong.
Operating on a live patient -
Debugging running containers
- no need for ssh
- … no need for nsenter
- $ docker exec -it my_container bash

52. Questions?
@attilczuk