07. Dockerfiles

Dockerfile pre-concepts

Dockerfiles

Dockerfiles are text files used to define Docker images. They contain commands used to define a source or parent image, copy files to the image, install software on the image, and define the application which will run when the image is invoked.

In the next video, you will walk through an example of a basic Dockerfile, with a discussion of the commands found on each line.

FSND C4 L1 A07 Dockerfile

Dockerfile Concept Summary

Recap

Dockerfiles define Docker Images. As seen in the example above, a Dockerfile typically starts with a source image upon which you can add layers to build your own custom image. For example, in the video above, the Dockerfile started with the source image python:3.7.2-slim : 

FROM python:3.7.2-slim

COPY . /app
WORKDIR /app

RUN pip install --upgrade pip
RUN pip install flask


ENTRYPOINT [“python”, “app.py”]

Additional layers in the Dockerfile can be used to install dependencies, like flask in the Dockerfile above. They can also be used to setup a working directory and define an entrypoint for your container. In the example above, the executable is app.py , which will be run when the container starts.

The image below summarizes the process of running a container starting from a Dockerfile:

Docker Container Creation

Docker files are used to build Docker Images. Docker images are run to create Docker Containers

Docker files are used to build Docker Images. Docker images are run to create Docker Containers

Dockerfile summary

Dockerfile Command Glossary

In the video example above, you were exposed to several common Dockerfile commands that can be used when creating your own Dockerfiles:

  • Dockerfile comments start with # .
  • FROM defines source image upon which the image will be based.
  • COPY copies files to the image.
  • WORKDIR defines the working directory for other commands.
  • RUN is used to run commands other than the main executable.
  • ENTRYPOINT is used to define the main executable.

Dockerfile Quizzes

Dockerfile Problem Set

Which command would you use to specify a wsgi server as the main executable?

SOLUTION: ENTRYPOINT ["gunicorn", "-b", ":8080", "main:APP"]

Dockerfile Problem Set

Which command would you use to specify python:3.7.2-slim as the source image?

SOLUTION: FROM python:3.7.2-slim

Dockerfile Problem Set

Which command would run ‘apt-get update -y’ in preparation to install dependencies on the image?

SOLUTION: RUN apt-get update -y

Summary

Summary

In this concept, you learned about Dockerfiles and how they are used to create Docker images. You saw an example of a Dockerfile built up in layers, starting with a single parent image and ending with a flask installation and an application entrypoint.

You also learned about some of the basic commands used to create Dockerfiles, including FROM , COPY , WORKDIR , RUN , and ENTRYPOINT .

In the next concept, you will create your own Docker containers starting with Dockerfiles.

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