Getting started with Docker Compose

Table of contents

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Prerequisite

1) Install Docker (Link – Docker setup)
2) Install Docker Compose (Link – Docker compose setup)

Lets gear up with the basics of Docker.

What is docker?

Docker is a tool designed to make it easier to create, deploy, and run applications by using containers. Containers allow a developer to package up an application with all of the parts it needs, such as libraries and other dependencies, and ship it all out as one package. By doing so, thanks to the container, the developer can rest assured that the application will run on any other Linux machine regardless of any customized settings that machine might have that could differ from the machine used for writing and testing the code.

In a way, Docker is a bit like a virtual machine. But unlike a virtual machine, rather than creating a whole virtual operating system, Docker allows applications to use the same Linux kernel as the system that they’re running on and only requires applications be shipped with things not already running on the host computer. This gives a significant performance boost and reduces the size of the application.

And importantly, Docker is open source. This means that anyone can contribute to Docker and extend it to meet their own needs if they need additional features that aren’t available out of the box.

Who is Docker for?

Docker is a tool that is designed to benefit both developers and system administrators, making it a part of many DevOps (developers + operations) toolchains. For developers, it means that they can focus on writing code without worrying about the system that it will ultimately be running on. It also allows them to get a head start by using one of thousands of programs already designed to run in a Docker container as a part of their application. For operations staff, Docker gives flexibility and potentially reduces the number of systems needed because of its small footprint and lower overhead.

I have cleared the basics of docker here and you can explore more from Docker Doc

What is docker Compose?

Compose is a tool for defining and running multi-container Docker applications. With Compose, you use a Compose file to configure your application’s services. Then, using a single command, you create and start all the services from your configuration.

Steps for implementing docker compose

1) Create your Dockerfiles for each services

2) Define services to run your application in docker-compose.yml file.

3) Start and run your entire application with the help of docker-compose.yml file.

1) Create a Dockerfile

Dockerfile is a text document where we specify all the commands which are required to run a service. Name it as Dockerfile and put this in the project directory.

Sample Dockerfile

#
# Scala and sbt Dockerfile
#
# https://github.com/hseeberger/scala-sbt
#

# Pull base image
FROM openjdk:8

ENV SCALA_VERSION 2.12.1
ENV SBT_VERSION 0.13.15

# Scala expects this file
RUN touch /usr/lib/jvm/java-8-openjdk-amd64/release

# Install Scala
## Piping curl directly in tar
RUN \
curl -fsL http://downloads.typesafe.com/scala/$SCALA_VERSION/scala-$SCALA_VERSION.tgz | tar xfz – -C /root/ && \
echo >> /root/.bashrc && \
echo ‘export PATH=~/scala-$SCALA_VERSION/bin:$PATH’ >> /root/.bashrc

# Install sbt
RUN \
curl -L -o sbt-$SBT_VERSION.deb http://dl.bintray.com/sbt/debian/sbt-$SBT_VERSION.deb && \
dpkg -i sbt-$SBT_VERSION.deb && \
rm sbt-$SBT_VERSION.deb && \
apt-get update && \
apt-get install sbt && \
sbt sbtVersion

# Define working directory
WORKDIR /root

2) Create docker-compose.yml file

Create a file named docker-compose.yml in your project directory.

Sample docker-compose.yml file

zookeeper:
image: zookeeper:3.4
ports:
– 2181:2181
kafka:
image: ches/kafka:latest
ports:
– 9092:9092
links:
– zookeeper:3.4
myElastic:
image: elasticsearch:2.4.0
ports:
– 9200:9200

This means you have specified all your services that you require to run the complete application. With these services you have to specify the image name, port which is to be run, links where we specify the dependencies of a particular service over any other service. So to start all the service in order to run the application we just need to up the docker-compose file and done. The application will be up and running.

3) Run docker-compose.yml file

Now we need to just up the docker-compose.yml file which will pull the images for the services specified(if not present in the local system).Command to up the container is docker-compose up and to stop is docker-compose stop. Note that you need to tranverse to the directory where the docker-compose.yml file is present and then you can explore the following commands.

Commands

You can check all the docker compose commands by typing docker-compose –help command on your terminal.

build Build or rebuild services
bundle Generate a Docker bundle from the Compose file
config Validate and view the compose file
create Create services
down Stop and remove containers, networks, images, and volumes
events Receive real time events from containers
exec Execute a command in a running container
help Get help on a command
images List images
kill Kill containers
logs View output from containers
pause Pause services
port Print the public port for a port binding
ps List containers
pull Pull service images
push Push service images
restart Restart services
rm Remove stopped containers
run Run a one-off command
scale Set number of containers for a service
start Start services
stop Stop services
top Display the running processes
unpause Unpause services
up Create and start containers
version Show the Docker-Compose version information