How Containers work?

• Refer Here for the docker internals.

Trails

• Every docker container has a command that gets executed when the container is created/started. As long as that command is running the container will be in running state, if that command has finished execution container will be stopped or exited

Lets create a docker container and install our application in it

• to run the container in the background mode (detached mode) we use -d
• The application which i want to run is apache server

sudo apt update
sudo apt install apache2 -y

• Apache runs on port 80
• Create a docker contianer with ubuntu image. Run it in the interactive mode.
• Ensure port forwarding is set

docker container run -p 8081:80 -it ubuntu:22.04 /bin/bash
# apt update
# apt install apache2 -y
# service apache2 start

• Now access the http://<ip of docker host>:8081
  
• This might run the application but is not a good way as i need to do installation for every container created.

Lets create a docker image by manually installing softwares in container

• Lets install a nginx in some container and create a image out of it
• lets create a container in a interactive mode

docker container run -p 8082:80 -it ubuntu:22.04 /bin/bash
# apt update
# apt install nginx -y
# service nginx start

• Now lets create a docker image from running container
• In the docker host

docker commit <container-name/id>

* Now lets create an image and tag based the image id

* This approach creates images but no history of changes are available.

Dockerfile approach

• Dockerfile approach is all about using instrcutions to inform docker what needs to be done when creating the image, starting the contianer. What are the metadata about your image
• Dockerfile has instructions to containerize the application.
• Dockerfile can be written in any text file, but file a name Dockerfile is most commonly used
• Lets take a very simple Dockerfile

FROM alpine:latest
CMD ["echo", "Welcome to container world"]

• Now lets try to build
• Create a new folder and create a file with name Dockerfile with the above content
  
• Now check images
  
• Lets run the container from the image