An Introduction to Docker using Examples

Gerard Keating


Docker is an open-source project that automates the deployment of Linux applications inside software containers.

Docker is an open-source project that automates the deployment of Linux applications inside software containers.

Software containers are Operating-system-level virtualization which is a computer virtualization method in which the kernel of an operating system allows the existence of multiple isolated user-space instances.

This presentation:

  • Where I use docker?
  • A Simple example
  • Docker Compose
  • An Example Project
  • Tips
  • To Research Further

Where I use docker?

  • CCPE's graphite system and grafana board 
  • Experimenting with new technologies, currently looking into Sonar Qube
  • Rapid prototyping new systems like "An Example Project"
  • Learning a new programming language
  • This presentation (before being moved to

A Simple example: Overview


A Simple example

A Python Flask "Hello World!" application

from flask import Flask
app = Flask(__name__)

def hello():
    return "Docker presentation"

if __name__ == "__main__":'', 80, debug=True)

Folder Structure

├── Dockerfile
└── src

A Simple example: Dockerfile

FROM python:2.7
MAINTAINER Gerard Keating <>
COPY src/ /app
RUN pip install flask
CMD python
docker build -t docker_example1:latest .
docker images

$ docker build -t docker_example1:latest .
Sending build context to Docker daemon 4.608 kB
Step 1 : FROM python:2.7
 ---> 6b494b5f019c
Step 2 : MAINTAINER Gerard Keating <>
 ---> Using cache
 ---> 8c96ad4ecd7c
Step 3 : COPY src/ /app
 ---> Using cache
 ---> 1068fdb21dd8
Step 4 : WORKDIR /app
 ---> Using cache
 ---> c482c92f1d29
Step 5 : RUN pip install flask
 ---> Using cache
 ---> 8014d50a37a4
Step 6 : CMD python
 ---> Using cache
 ---> 44b55fc47d09
Successfully built 44b55fc47d09

$ docker images
REPOSITORY      IMAGE ID        CREATED             SIZE             TAG
docker_example1 44b55fc47d09    About an hour ago   682.4 MB         latest

A Simple example: running the instance

docker run -p 3000:80 --name docker_example1_inst docker_example1
docker ps

Docker Compose

Compose is a tool for defining and running multi-container Docker applications
Basically a wrapper for docker
Note: Not recommended for production nor for managing 10+ containers

Also useful for running just one container

  • Deals with names of containers
  • Deals with deleting, keeping and building containers and images
  • Don't need to remember all the docker arguments or write a bash script

Docker Compose

For docker compose to work you need a yaml(docker-compose.yml) file
Here's an example

version: '2'
        build: .
            - 3000:80

Then similiar to before

docker-compose build
docker-compose up


An Example Project: Requirements

  • Get information from a sql server
  • Run something on that data and store data in mongo db for later analysis


New Compose File

version: '2'

    image: mongo
      - ./mongodb_data:/data/db
      - "27017:27017"

    build: .
     - ./src:/app
      - secure.env


FROM ubuntu:xenial
# Update the sources list
RUN apt-get update

# Install Python and Basic Python Tools
RUN apt-get install -y python python-dev python-distribute python-pip
RUN pip install --upgrade pip
# mssql connect stuff
RUN apt-get install -y freetds-bin freetds-common freetds-dev unixodbc unixodbc-dev tdsodbc
RUN apt-get install -y libcurl3
ADD requirements.txt /
RUN pip install -r /requirements.txt

ADD odbcinst.ini /etc/odbcinst.ini

# Copy the application folder inside the container
ADD src /app

WORKDIR "/app"

CMD python

docker creates it's own network with dns so to connect to the mongo db from python is just

client = pymongo.MongoClient("db")

$ docker-compose build
db uses an image, skipping
Building monitor
Step 1/12 : FROM ubuntu:xenial
 ---> 0ef2e08ed3fa
Step 2/12 : RUN apt-get update
 ---> Using cache
 ---> 8d6511968ecd
$ docker-compose up
Creating sixsmonitor_db_1
Creating sixsmonitor_monitor_1
Attaching to sixsmonitor_db_1, sixsmonitor_monitor_1
db_1       | 2017-05-31T09:24:59.086+0000 I CONTROL  [initandlisten] MongoDB starting : pid=1 port=27017 dbpath=/data/db 64-bit host=d191ae6b54cf
db_1       | 2017-05-31T09:24:59.086+0000 I CONTROL  [initandlisten] db version v3.4.3
db_1       | 2017-05-31T09:24:59.086+0000 I CONTROL  [initandlisten] git version: f07437fb5a6cca07c10bafa78365456eb1d6d5e1
db_1       | 2017-05-31T09:24:59.086+0000 I CONTROL  [initandlisten] OpenSSL version: OpenSSL 1.0.1t  3 May 2016
db_1       | 2017-05-31T09:24:59.086+0000 I CONTROL  [initandlisten] allocator: tcmalloc
db_1       | 2017-05-31T09:24:59.086+0000 I CONTROL  [initandlisten] modules: none
db_1       | 2017-05-31T09:24:59.086+0000 I CONTROL  [initandlisten] build environment:
db_1       | 2017-05-31T09:24:59.086+0000 I CONTROL  [initandlisten]     distmod: debian81
db_1       | 2017-05-31T09:24:59.086+0000 I CONTROL  [initandlisten]     distarch: x86_64
db_1       | 2017-05-31T09:24:59.086+0000 I CONTROL  [initandlisten]     target_arch: x86_64
db_1       | 2017-05-31T09:24:59.086+0000 I CONTROL  [initandlisten] options: {}
db_1       | 2017-05-31T09:24:59.088+0000 W -        [initandlisten] Detected unclean shutdown - /data/db/mongod.lock is not empty.
db_1       | 2017-05-31T09:24:59.095+0000 I -        [initandlisten] Detected data files in /data/db created by the 'wiredTiger' storage engine, so setting the active storage engine to 'wiredTiger'.
db_1       | 2017-05-31T09:24:59.098+0000 W STORAGE  [initandlisten] Recovering data from the last clean checkpoint.
db_1       | 2017-05-31T09:24:59.099+0000 I STORAGE  [initandlisten] wiredtiger_open config: create,cache_size=487M,session_max=20000,eviction=(threads_min=4,threads_max=4),config_base=false,statistics=(fast),log=(enabled=true,archive=true,path=journal,compressor=snappy),file_manager=(close_idle_time=100000),checkpoint=(wait=60,log_size=2GB),statistics_log=(wait=0),
monitor_1  | 2017-05-31 09:24:59,336 monitor:213 INFO:Script started
monitor_1  | 2017-05-31 09:24:59,337 monitor:25 DEBUG:Connecting to cdm
monitor_1  | 2017-05-31 09:24:59,618 monitor:27 DEBUG:Connected to cdm


  • Try and keep each docker container doing only one thing
  • Keep your build times short by putting frequently changed things near the end of your docker file
  • docker technology is still moving fast, good news bugs fixed fast, bad news things are constantly changing

To Research Further

  • Windows running in a docker container: looked into it before but found alot of new licenses needed
  • Container orchestration: i.e. how to manage 100s of containers with technologies like kubernetes and docker swarm
  • docker security: how easy is it to escape a docker container? docker diff and docker readonly filesystems, Scanning docker images for CVES (docker supply a service for this called Docker Security Scanning)



Anymore questions please e-mail me at

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By gerardk

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An quick introduction to docker using a flask python example

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