Docker in everyday development

Docker in everyday
development
What every dev should know.

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/

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

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

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

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

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.

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

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

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

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

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

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

Docker + Vagrant
Containers on VMs

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

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

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

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

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

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

https://www.flickr.com/photos/pasukaru76/9824401426/in/photolist-9DE7Wa-cd6Wxf-dLkpKN-bW4iP-6TfKoP-okpdNP-
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Containers everywhere
$ docker rmi
$ docker rm

Time for a better tool
Docker Compose

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

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

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

redis:
image: redis
volumes:
- /var/docker/redis:data
ports:
- “6379”

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

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

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/

All is rainbows and unicorns now,
right?

Compose - good for running
containers
But missing dependencies.

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

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

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

Automate everything.
Use smart technologies.
Use Make.

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

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

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

Docker in everyday development

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