2. Docker for Application Packaging

Note

Make sure you have prepared the environment for this task.

Solution 2.1 - Create Dockerfile

1. Create Dockerfile: touch Dockerfile

2. Open the Dockerfile.

3. Create layers due to task:

# syntax=docker/dockerfile:1

FROM golang:1.16-alpine

WORKDIR /go/src/app

ADD . .

RUN go mod init

RUN go build -o go-helloworld

EXPOSE 8080

CMD ["./go-helloworld"]

4. Save changes

Solution 2.2 - Build a Docker Image

1. Make sure you are in the /exercises/go-helloworld/ directory.

2. Build a Docker image using the prompt command:

docker build -t go-helloworld .

Solution 2.3 - Push a Docker Container to Docker Hub

Note

To push a Docker container to Docker Hub, you need to have a Docker Hub account

Follow these steps to push a Docker container to Docker Hub:

1. Run a Docker image as a container: docker run -p 8080:8080 --name go_moriarty -d go-helloworld

2. Verify if the application at: http://127.0.0.1:8080/

3. Login to the Docker Hub: docker login -u "YOUR_DOCKERHUB_USERNAME" -p "YOUR_DOCKERHUB_PASSWORD" docker.io

4. Tag the image: docker tag go-helloworld YOUR_DOCKERHUB_USERNAME/go-helloworld:v1.0.0

5. Push the image to the DockerHub repo: docker push YOUR_DOCKERHUB_USERNAME/go-helloworld:v1.0.0

Feel free to check the video Docker for Application Packaging

2.4 Pull Image From the Docker Hub

Remove all builds and images:

• Explore the processes: docker ps -a

• Stop the container: docker stop go_moriarty

• Remove the container: docker rm go_moriarty

• Explore the images: docker images

• Remove the image from local machine: docker rmi YOUR_DOCKERHUB_USERNAME/go-helloworld:v1.0.0

Pull container from your Docker Hub repository:

• Pull the image: docker pull YOUR_DOCKERHUB_USERNAME/go-helloworld:v1.0.0

• Run the image as a container: docker run -p 8080:8080 --name go_pulled -d YOUR_DOCKERHUB_USERNAME/go-helloworld:v1.0.0

• Verify go-helloworld application at: http://127.0.0.1:8080/

Useful Docker Commands

• Get container name: docker ps -a

• Stop the container: docker stop CONTAINER_NAME

• Remove the container: docker rm CONTAINER_NAME

• Stop all the processes: docker kill $(docker ps -q)

• Remove all the processes: docker rm $(docker ps -a -q)

• Remove all the images: docker rmi $(docker images -q)

Find out more helpful commands in the Docker Cheat Sheet.

Solution 2.5 - Dockerize Python Flask Application

In this step, we have gained a basic understanding of containerizing applications with Docker. So let’s take a look at the process of dockerizing a Pyhton Flask application.

Use this recipe to put your Python Flask application in a Docker container and push it to the Docker Hub:

1. Install Docker if not have it yet: sudo apt-get install docker.io

2. Activate Python virtual environment: source venv/bin/activate

3. Change working directory: cd exercise/python-helloworld

4. Create a Dockerfile:

# syntax=docker/dockerfile:1

FROM python:3.8

WORKDIR /app

COPY . /app

RUN pip install -r requirements.txt

EXPOSE 5000

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

3. Run the Docker image: docker run -p 5000:5000 --name monty_python -d python-helloworld

4. Verify if the application is available and work properly at: http://127.0.0.1:5000/

5. Build a Docker image: docker build -t python-helloworld .

6. Tag application: docker tag python-helloworld YOUR_DOCKERHUB_USERNAME/python-helloworld:v1.0.0

7. Login to Docker Hub: docker login

8. Push the application to Docker Hub: docker push YOUR_DOCKERHUB_USERNAME/python-helloworld:v1.0.0

Common Errors & How to Fix Them

Permission Denied Error

Error

Got permission denied while trying to connect to the Docker daemon socket at unix:///var/run/docker.sock: Post http://%2Fvar%2Frun%2Fdocker.sock/v1.24/build?buildargs=%7B%7D&cachefrom=%5B%5D&cgroupparent=&cpuperiod=0&cpuquota=0&cpusetcpus=&cpusetmems=&cpushares=0&dockerfile=Dockerfile&labels=%7B%7D&memory=0&memswap=0&networkmode=default&rm=1&shmsize=0&t=go-helloworld&target=&ulimits=null&version=1: dial unix /var/run/docker.sock: connect: permission denied`

To fix Permission Denied Error, follow the next steps:

1. Create the docker group: sudo groupadd docker

2. Add your user to the docker group: sudo usermod -aG docker ${USER}

3. Set the superuser: su -s ${USER}

4. Check if Docker work correctly: docker ps -a

5. Build Docker image: docker build -t go-helloworld .

Follow the link to learn more about how to fix Permission Denied Error.

File Not Found Error

Error

go: go.mod file not found in current directory or any parent directory; see 'go help modules'

This error refers to building a Docker image for the Golang application and means you need to init go.mod file. To fix File Not Found Error, follow these steps:

1. Open the Dockerfile of your Go application.

2. Add RUN go mod init layer before the RUN go build -o helloworld layer.

3. Save the changes.

4. Build Docker image using docker build -t go-helloworld . command.

After these manipulations, the Dockerfile should look like this:

FROM golang:alpine

WORKDIR /go/src/app

ADD . .

RUN go mod init

RUN go build -o helloworld

EXPOSE 8080

CMD ["./helloworld"]