(Day 14) Task : Docker Port Expose :-

• Exposing and publishing ports in Docker is essential for enabling communication between your containerized applications and the external world. This guide breaks down the concepts and provides simple, step-by-step instructions to help you manage Docker ports effectively.

• In this session we’ll learn how will the user access the content of a container through internet.

• Container doesn’t have any ip and to access anything using internet ip is required.

• Internet Access Port : 80.

• Since , there is a mapping b/w ec2 instance & container when a user runs that instance using public ip in its device remotely then it’ll go to the ec2 instance & since mapping is there user will be able to see content of container that may be website or anything.

Understanding Docker Ports

• EXPOSE: A Dockerfile instruction that documents which ports the container listens on. It doesn't publish the port to the host machine.

• -p / --publish: A Docker run command option that maps a container's port to a port on the host, making it accessible externally.

• -P / --publish-all: Automatically maps all exposed ports to random ports on the host.

How to Expose and Publish Ports

Difference between docker attach and docker exec :-

Docker attach :

• Functionality: Attaches your terminal to the container's main process, allowing you to interact as if you were directly connected to it.

• Behavior:

  • Input and output are shared; what you type is sent to the container, and its output is displayed in your terminal.

  • If the container was started with -i (interactive), your inputs are directed to its stdin.

  • Exiting the attach session (e.g., via CTRL+C) can stop the container if the main process terminates as a result.

Docker exec :

• Functionality: Executes a new command in a running container, creating a separate process from the main application.

• Behavior:

  • Each exec session is independent, allowing multiple concurrent sessions.

  • Does not interfere with the main process; exiting the exec session leaves the container running.

  • Supports running commands as different users within the container.

Difference between Expose and Publish(-p) :-

Basically we have Four Options:

1. Neither Specify Expose nor publish(-p) :

   The service in the container will only be accessible from inside container only.

2. Only Specify Expose :

   In this , Service won’t be accessible from outside Docker , but from inside other Docker Containers Can.

3. Specify Expose and publish(-p):

   The Service can be accessible from anywhere , even outside Docker.

4. Only Specify publish(-p) :

   Docker does an implicit expose. This is because , if a port is open to public , it’s also open to other docker containers hence , -p includes expose.