Walkthrough containerizing application

Table of Contents

• 1. Running the app in traditional way
  • 1.1. Start redis server
  • 1.2. Start flask server
  • 1.3. Check if app is running
• 2. Running app in container
  • 2.1. Containerize flask app
  • 2.2. Multi-container app definition
  • 2.3. Bring up the application
  • 2.4. Check if the app is running

1. Running the app in traditional way

1.1. Start redis server

• Install redis

$ sudo dnf -y install git redis python2-virtualenv python-pip python-devel

• Start redis server

$ sudo systemctl start redis

1.2. Start flask server

• Clone this repository

$ git clone https://github.com/container-workbook/docker-workshop/
$ cd docker-workshop/pyconapp/

• Create a python virtualenv

$ virtualenv venv
$ . venv/bin/activate
(venv) $

• Install all the requirements

(venv) $ pip install -r requirements.txt

• Start flask app

(venv) $ export REDIS_HOST=127.0.0.1
(venv) $ python app.py

1.3. Check if app is running

$ curl 127.0.0.1:5000
<h3>Hello Pythonistas</h3> <br/><h2>Number of Hits:</2> 1<br/>

2. Running app in container

2.1. Containerize flask app

• Create Dockerfile that looks like this:

$ cat Dockerfile
FROM fedora:24

RUN dnf update -y && \
    dnf install -y python-pip python-devel

ADD https://raw.githubusercontent.com/vishnubob/wait-for-it/master/wait-for-it.sh /usr/local/bin/wait-for-it.sh

RUN chmod +x /usr/local/bin/wait-for-it.sh && mkdir -p /app

WORKDIR /app
COPY . /app

RUN pip install -r requirements.txt

EXPOSE 5000

ENTRYPOINT /app/entrypoint.sh

• Create an entrypoint.sh file which looks like this:

$ cat entrypoint.sh
#!/bin/bash

/usr/local/bin/wait-for-it.sh REDIS_HOST:6379

cd /app
python app.py

• Add permissions to entrypoint.sh

$ chmod +x entrypoint.sh

2.2. Multi-container app definition

• Create a docker-compose.yml file that defines multi-container application

$ cat docker-compose.yml
version: '2'

services:
  redis:
    image: redis:latest
    ports:
      - "6379"

  app:
    build: .
    ports:
      - "5000"
    environment:
      - REDIS_HOST=redis

2.3. Bring up the application

$ docker-compose up

2.4. Check if the app is running

• Find out the port flask app is exposed on:

$ docker ps | grep pyconapp_app

• curl on it:

$ curl 127.0.0.1:32774
<h3>Hello Pythonistas</h3> <br/><h2>Number of Hits:</2> 1<br/>

So that’s how you can migrate an app that is monolithic and containerize it.