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Build

⬅️ Back to Docker overview

Show all local images

docker images

Download a python image from Docker hub.

docker pull python

💡 Docker Desktop depicts the images as well.

Delete all images on the host

docker rmi $(docker images -aq)

Build a docker image without a Tag

docker build .
  • 💡 If you are using build . without any further options the image will only have an ID.
  • 💡 The example app can be found in the folder simple-docker-app.

Add a tag and a version

docker build . -t webapp-color:0.1
  • 💡 docker build -t username/image_name:tag_name .
  • 💡 Tags are aliases to the ID of your image.
  • 💡 Whenever an image is tagged without an explicit tag, it’s given the latest tag by default.

Run the self build image

docker run -d -p 8010:8080 webapp-color:0.1

Visit the website http://localhost:8010

Set environment variables with the option --env or -e

docker run -d --name blue-app -e APP_COLOR='blue' -p 38282:8080 webapp-color:0.1

Visit the website http://localhost:38282

  • 💡 Variables have the following format: KEY=value
  • 💡 Inside the container you can also use the echo command to print a shell variable. echo $KEY
  • 💡 The option -e can be used multiple times.
  • 💡 Not all colours are available. You can use red, green, blue, blue2 or pink.

🚧 TODO: Merge with exercise below. Differentiate between tips & exercise more cleanly

Exercise

  • 📝 Build your own image based on the given example with following image name and tag my-webapp:1.0. The source code can be found here https://github.com/kodekloudhub/webapp-color
  • 📝 Inspect the Dockerfile. Where is your application code stored inside the container and how is declared that the port inside the container is 8080?
  • 📝 Optional: Deploy a MySQL database using the mysql image and name it mysql-db. Set the database password to use db_pass123. Lookup the MySQL image on Docker Hub and identify the correct environment variable to use for setting the root password.

command vs. entrypoint

  • Containers are not meant to run an operating system. Container are meant to run a specific tasks or process. and only lives as long the process is alive.
  • A CMD defines the programs that would be run within the container when it starts. CMD for nginx or mysqld. ubuntu run bash, if it can not find a terminal it exists.
  • Immediately disappears docker run ubuntu

Replace the CMD entirely. It waits for 5 seconds and disappears.

docker run ubuntu sleep 5

Build your own Dockerfile with default 5 seconds sleep.

  • Dockerfile:
  • FROM ubuntu
  • CMD sleep 5
docker build . -t ubuntu_sleeper
docker run ubuntu_sleeper

Entrypoint, command line parameters will be appended

  • Dockerfile:
  • FROM ubuntu
  • ENTRYPOINT ["sleep"]
  • CMD ["1"]
docker build . -t ubuntu_sleeper
docker run ubuntu_sleeper 10

💡 Without no CMD and no parameter you would get the following error: sleep: missing operand 💡 The entrypoint can be overwritten with the entrypoint --entrypoint option.