Exposing ports to host in Docker - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does it mean to expose a port in Docker?

Exposing a port means making a port inside the Docker container accessible from the host machine or other containers. It allows communication between the container and the outside world.

beginner

Which Docker command option is used to expose a container port to the host?

The -p or --publish option is used with docker run to map a container port to a host port, like -p 8080:80.

beginner

Explain the syntax -p 8080:80 in Docker port mapping.

It means map port 80 inside the container to port 8080 on the host. So, accessing localhost:8080 on the host reaches port 80 in the container.

intermediate

What is the difference between EXPOSE in Dockerfile and -p in docker run?

EXPOSE in Dockerfile is a hint that the container listens on a port but does not publish it. -p in docker run actually maps the port to the host.

beginner

Can you expose multiple ports from a container to the host? How?

Yes, by using multiple -p options in docker run, for example: -p 8080:80 -p 8443:443 to expose HTTP and HTTPS ports.

Which Docker command option exposes a container port to the host?

A -p

B -e

C -v

D -d

The -p option maps container ports to host ports, exposing them.

What does -p 3000:3000 do in docker run?

A Maps container port 3000 to host port 80

B Runs container in detached mode

C Exposes port 80 inside the container

D Maps host port 3000 to container port 3000

It maps port 3000 on the host to port 3000 inside the container.

What is the purpose of the EXPOSE instruction in a Dockerfile?

A To publish ports to the host

B To document which ports the container listens on

C To start the container

D To set environment variables

EXPOSE is a documentation hint and does not publish ports.

How do you expose multiple ports from a container?

A Use -e option multiple times

B Use multiple EXPOSE lines in Dockerfile only

C Use multiple -p options in docker run

D Use -d option multiple times

Multiple -p options map multiple ports to the host.

If you run docker run -p 8080:80, how do you access the container's service?

A By visiting localhost:8080 on the host

B By visiting localhost:80 on the host

C By visiting container IP:8080

D By visiting container IP:80

Port 80 in the container is mapped to port 8080 on the host.

Describe how to expose a container port to the host using Docker commands.

Think about how to connect container ports to your computer ports.

Explain the difference between EXPOSE in Dockerfile and the -p option in docker run.

One is for documentation, the other for actual port access.