Docker Tutorial For Beginners : Part 3

Abhishek Ghosh

By Abhishek Ghosh July 17, 2017 7:54 am Updated on July 17, 2017

Docker Tutorial For Beginners : Part 3

In this series, first part of guide was on how to install Docker and use commands, second part was installation of some UI to visually check what is going on. In Part 3 of Docker Tutorial For Beginners, we will learn basics about Docker File, Port, Containers, Environment, Registry and Tag. Normally if we write a Python application, we install a Python runtime on the machine. But, with Docker, we use a portable Python runtime as an image without actual installation on real machine. So achieve the goal, we need a direction file. That direction file is Dockerfile. Additionally, there will be a requirements text file listing what Python stuffs needed. Examples are given with Python because it is easy.

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Docker Tutorial For Beginners : How To Create A Docker Application & Make it Running

We talked about Dockerfile. You can create an empty directory, take that it is located at /app. Then create 3 files inside it :

touch Dockerfile
touch requirements.txt
touch app.py

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touch Dockerfile

touch requirements.txt

touch app.py

That Dockerfile will have this content :

FROM python:2.7-slim
WORKDIR /app
ADD . /app
RUN pip install -r requirements.txt
EXPOSE 80
ENV NAME World
CMD ["python", "app.py"]

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FROM python:2.7-slim

WORKDIR /app

ADD . /app

RUN pip install -r requirements.txt

EXPOSE 80

ENV NAME World

CMD ["python", "app.py"]

requirements.txt will have this content :

Flask
Redis

1 2	Flask Redis

app.py will have this content :

from flask import Flask
from redis import Redis, RedisError
import os
import socket

# Connect to Redis
redis = Redis(host="redis", db=0, socket_connect_timeout=2, socket_timeout=2)

app = Flask(__name__)

@app.route("/")
def hello():
    try:
        visits = redis.incr("counter")
    except RedisError:
        visits = "<i>cannot connect to Redis, counter disabled</i>"

    html = "<h3>Hello {name}!</h3>" \
           "<b>Hostname:</b> {hostname}<br/>" \
           "<b>Visits:</b> {visits}"
    return html.format(name=os.getenv("NAME", "world"), hostname=socket.gethostname(), visits=visits)

if __name__ == "__main__":
    app.run(host='0.0.0.0', port=80)

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from flask import Flask

from redis import Redis, RedisError

import os

import socket

# Connect to Redis

redis = Redis(host="redis", db=0, socket_connect_timeout=2, socket_timeout=2)

app = Flask(__name__)

@app.route("/")

def hello():

try:

visits = redis.incr("counter")

except RedisError:

visits = "<i>cannot connect to Redis, counter disabled</i>"

html = "<h3>Hello {name}!</h3>" \

"<b>Hostname:</b> {hostname}<br/>" \

"<b>Visits:</b> {visits}"

return html.format(name=os.getenv("NAME", "world"), hostname=socket.gethostname(), visits=visits)

if __name__ == "__main__":

app.run(host='0.0.0.0', port=80)

The above is official example. Now we need to learn how to build those 3 files to Docker app, tag it and run it. Let us run the commands :

docker build -t newexamplepython .
docker images
docker run -d -p 4000:80 newexamplepython
docker ps

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docker build -t newexamplepython .

docker images

docker run -d -p 4000:80 newexamplepython

docker ps

Now, if you point your browser to http://localhost:4000, you’ll see the Python application running.

Next steps are optional and demonstration of how to push the application to some service, in the way we push application to GitHub repo. In part 2, we talked about Docker cloud. You need an account and run :

docker login
# example tag
docker tag newexamplepython abhishekghosh/get-started:part3
docker images
docker push abhishekghosh/get-started:part3

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docker login

# example tag

docker tag newexamplepython abhishekghosh/get-started:part3

docker images

docker push abhishekghosh/get-started:part3

You can see the format of the commands used above :

docker <command> username/repository:tag

1	docker <command> username/repository:tag

Now from that “repo”, we can “pull” the image on any computer and run it exactly like normally we can do with some Node.js app from Github.

Practice these steps with applications in different programming languages, combine with different Databases and test.

Tagged With Microsoft , docker tutorials , docker voor beginners

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