How To Execute A Dockerfile | Build And Run Workflow

To execute a Dockerfile, you build a Docker image from it using docker build and then run a container from that image using docker run.

The most common mistake new Docker users make is treating a Dockerfile like a shell script. You can’t just hit “run” on it. A Dockerfile is a set of instructions for building a Docker image, and that image is what actually runs as a container. Mastering “how to execute a Dockerfile” means learning this two-step choreography: docker build then docker run.

Executing A Dockerfile: The Build And Run Workflow

A Dockerfile is a blueprint. The docker build command executes its instructions to create a portable snapshot called an image. The docker run command takes that image and spins it up as a live container. You never run the file itself — you run the output it produces.

Understanding this distinction is the gateway to containerization. The Docker Engine reads each instruction in the file line by line, creates a temporary intermediate container for each step, and saves the result as a layered image. That final image is executable. The file is not.

How To Build An Image From A Dockerfile

Here is the exact workflow to write, build, and run your first container from a Dockerfile. Follow these steps exactly to avoid the common pitfalls.

Step 1: Create a Dedicated Directory

Don’t drop a Dockerfile into your home or root directory. The build context includes every file in the current directory, and building from a messy folder will slow things down or cause errors.

mkdir ~/my-project && cd ~/my-project

Step 2: Create the Dockerfile

The filename is conventionally Dockerfile with a capital D. Use any text editor to create it.

touch Dockerfile
nano Dockerfile

Step 3: Write Your Instructions

Start with a base image using FROM. Add the commands needed to set up your application.

FROM python:3.11-slim
WORKDIR /app
COPY . /app
RUN pip install -r requirements.txt
CMD ["python", "app.py"]

Step 4: Build the Image

Run the docker build command from within your project directory. The -t flag tags the image with a name.

docker build --tag my-app .

Step 5: Run a Container from the Image

Once the build completes, spin up a container using the image name you just tagged.

docker run my-app

If your CMD was ["python", "app.py"], your application will start running in the terminal. You have just executed your Dockerfile.

Core Dockerfile Instructions Reference

These are the most frequently used building blocks for any Dockerfile. Master these, and you can containerize almost any application.

Why Can’t I Just Run The Dockerfile Directly?

There is no docker run Dockerfile command. The Dockerfile isn’t executable — it is a source file read by the Docker builder. Trying to run it directly is like trying to execute a blueprint instead of the building built from it.

The Three Most Common Mistakes

• Wrong order of operations: RUN commands execute during the build. Anything needed for the application must be installed before the final CMD sets the startup behavior.
• Not pinning your base image: Using FROM python:latest can pull a different version next month and silently break your app. Pin to a specific tag like python:3.11-slim for reproducible builds.
• Bad build context: Running docker build from $HOME sends your entire home directory to the Docker daemon. Always use a clean project folder. Docker’s official guide on building and tagging images covers these best practices in depth.

Useful docker run Flags For Real Applications

Running a basic container is just the start. These flags control how the container interacts with the host system and handle production scenarios.

How To Share Your Image On Docker Hub

Once your image works locally, you can share it or deploy it from anywhere. Log in to Docker Hub using the CLI, tag your image with your username, and push it up.

docker login
docker tag my-app your-username/my-app
docker push your-username/my-app

The Complete Dockerfile Workflow At A Glance

This is the entire cycle. Commit it to memory and every container task will follow this same shape.

1. Prepare: Create a project folder and write your Dockerfile.
2. Build: Run docker build -t your-image . to create the image.
3. Run: Run docker run your-image to start a container.
4. Share: Run docker push your-username/your-image to upload it.

You never execute the file itself. You execute the image it builds.