Docker + Java
Elek Márton
@anzix
2015 March
DPC Consulting

Docker+Java

What is docker
● Lightweight virtualization
– Container
● Repository of virtual images
– 100 official image
– ~45000 public images
● Versioning support
– To upgrade a container
● Only for linux
– Just a filesystem, the kernel of the host system is used
– Windows out of scope
● Similar to
– BSD jails, Linux LXC, Solaris zones

Docker run

Docker run

Docker run

Two main use case
Start a predefined
container
docker run jenkins
Start a command in a
well defined env
docker run ubuntu
uname -a
docker run ubuntu
bash

Volumes
● Every container is a one time container.
– All of the files will be deleted together with the container
● What about persisted data?
– Solution: volumes
docker run -v /root/jenkins:/var/jenkins_home
jenkins

● How to access?
– By default docker containers use internal unique IP
– An additional process forwards ports
● Port forwards should be defined
docker run -v /root/jenkins:/var/jenkins_home
-p 4567:8080 jenkins
Port forward

Create a docker container
● Snapshot an existing container
– Easy but non reproducible
– docker commit
● Create step-by-step from an existing container
– docker build .
FROM java:8
ADD build/version /app/version
WORKDIR /app
CMD ["bin/start.sh"]

● Usually one process
“In almost all cases, you should only run a single
process in a single container.
Decoupling applications into multiple containers makes
it much easier to scale horizontally and reuse
containers. If that service depends on another service,
make use of container linking.”
Docker best practices
What is inside a container

Docker ps

Upload to a repository
● docker push/pull
● Very similar to the git concept
– Versions
– Tagging
docker images
docker tag 8dbd9e392a dpc.hu:5000/backend
docker push dpc.hu:5000/ubuntu
Repository servers:
● docker
● artifactory

Docker definition
“Docker is an open platform for developers and
sysadmins to build, ship, and run distributed
applications.
Consisting of Docker Engine, a portable,
● lightweight runtime and
● packaging tool, and
● Docker Hub, a cloud service for sharing
applications and automating workflows”

Docker definition
“… Docker enables apps
to be quickly assembled from components
● and eliminates the friction between
● development, QA, and production
environments.”
“As a result, IT can ship faster and run the same app,
unchanged, on laptops, data center VMs, and any
cloud.”

What is missing
● How to create an alias for a complex command line
– Docker compose (was fig)
– Crane
● How to manage multiple machines all
together/schedule containers
– Kubernetes, OpenShift
● Hande logical group of containers together
– Kubernetes, OpenShift

Docker is ecosystem
● ContainerOS
– CoreOS, Project Atomic, Boot2Docker
● Open source PaaS
– Flynn, Dokuu, Deis
● Scheduler/Orchestration/Management
– Kubernetes, Crane, Docker Compose(fig)
● Continuous Integration
– Jennkins plugins, …
See also https://www.mindmeister.com/389671722/docker-ecosystem

(Without) Docker compose
docker run --name mysqldb
-e MYSQL_USER=mysql
-e MYSQL_PASSWORD=mysql
-e MYSQL_DATABASE=sample
-e MYSQL_ROOT_PASSWORD=supersecret
-d mysql
docker run --name mywildfly --link mysqldb:db
-p 8080:8080
-d arungupta/wildfly-mysql-javaee7

Docker compose
mysqldb:
image: mysql:latest
environment:
MYSQL_DATABASE: sample
MYSQL_USER: mysql
MYSQL_PASSWORD: mysql
MYSQL_ROOT_PASSWORD: supersecret
mywildfly:
image: arungupta/wildfly-mysql-javaee7
links:
- mysqldb:db
ports:
- 8080:8080

Use it from Windows/OSX/...
● Boot2docker
– Minimal virtual container (Virtualbox)
– Tools to run containers in the Virtualbox
● Docker Machine installer
– Windows/Linux/OSX

Who uses it?
● All of the big players:
● Amazon Beanstalk
– Dedicated container based hosting
● Google Cloud Platform
– Containers on Google Cloud Platform powered by
kubernetes
● RedHat OpenShift v3
– The new version is based on kubernetes/docker
● HP
– Operations Orchestration
And others...

Docker+Java

Example standalone app
Dockerfile
FROM java:8
WORKDIR /myapp
CMD ["bin/myproj"]
COPY build/install/myproj /myapp
mvn install/gradle package
docker build .
//upload to the repository with docker push
docker pull dpc.hu:5000/backend
docker run dpc.hu:5000/backend

Example J2EE application
FROM jboss/wildfly
RUN add-user.sh admin Admin#70365 --silent
CMD ["/opt/jboss/wildfly/bin/standalone.sh", "-b",
"0.0.0.0", "-bmanagement", "0.0.0.0"]
COPY target/helloworld.war
/opt/jboss/wildfly/standalone/deployments/

Recipes
● Arun Gupta:
9 Docker recipes for Java EE
Applications
– Use Docker Machine
– Link local mysql and wildfly together
– Link remote containers
– Deploy Java EE Application from Eclipse

Maven/SBT/Gradle
docker plugin

Artifactory

Continuous Deployment
See: Delivery pipline and zero downtime

Arquilian Cube (1.0.0 Alpha4)
“With this extension you can start a Docker container with a server installed,
deploy the required deployable file within it and execute Arquillian tests.
The key point here is that if Docker is used as deployable platform in
production, your tests are executed in a the same container as it will be in
production, so your tests are even more real than before.
But it also lets you start a container with every required service like database,
mail server, … and instead of stubbing or using fake objects your tests can use
real servers.”
https://github.com/arquillian/arquillian-cube

Summary
● Container technology is the present
– lightweight virtualization
– packaging
– repository
● Reusable components
– Continuous delivery
– Use exactly the same environment
– limit resources
– Easy to create test containers
● Growing ecosystem
– Supported solutions from the biggest vendors to the
smallest startup