Dockerizing a Simple Python Flask Application

Dockerizing a simple python flask application is a simple and easy task to understand the basics of docker file and also to grab the concept of python-flask. For this task we will be using a basic hello world flask application

EXPLANATION OF DOCKER FILE

Here is the complete docker file to setup the docker image for the application.

FROM python:alpine3.7
MAINTAINER Syed Saad Ahmed, syedsaadahmed2094.sa@gmail.com
COPY . /app
WORKDIR /app
RUN pip install -r requirements.txt
EXPOSE 5000
CMD python ./index.py

FROM python:alpine3.7

The FROM command is used to state what OS you intend to use as the base image. In this line we are inheriting our image from alpine 3.7 python image, As we will deploy a python app, so we have used alpine python image.

MAINTAINER Syed Saad Ahmed, syedsaadahmed2094.sa@gmail.com

The name or other info of the person who is the maintainer of particular docker file.

COPY . /app

To copy files from your Docker host to a Docker image, you can use the COPY command. We are copying all the files from our directory to docker images at /app

WORKDIR /app

WORKDIR allows you change directory while Docker builds the image, and the new directory remains the current directory for the rest of the build instructions.

RUN pip install -r requirements.txt

While building a Docker image, you may need to run commands for reasons such as installing applications and packages to be part of the image.

EXPOSE 5000

You’ll use the EXPOSE command to choose what ports should be available to communicate with a container. When running Docker containers, you can pass in the -p argument known as publish, which is similar to the EXPOSE command.

CMD python ./index.py

Docker can run only one CMD command. Therefore, if you insert two or more CMD instructions, Docker would only run the last one i.e. the most recent one. ENTRYPOINT is similar to CMD, however, you can run commands while launching and it wouldn’t override the instructions you’ve defined at ENTRYPOINT.

EXECUTING THE APPLICATION

Building the docker image first

docker build -t sample_image .

Here, sample_image is the name of the Docker image. You can give it another name. The dot (.) at the end of the command indicates that the files you’re working with are in the current directory.

Running the docker container

docker run -itd --name python-app -p 5000:5000 sample_image

Here, python-app is the name of your container that will be started, docker run has multiple flags like -i, -t, -d. you can explore them in docker official docs here, -p flag is used to publish/expose the port of container to the host.

Here is the Output

https://localhost:5000/

Checking the logs of your application

docker logs <container_id>

Furthermore here is the URL for the github repository for this complete application and setup.
https://github.com/syedsaadahmed/Dockerizing_Python_App