Summary - Port mapping

Combine port mapping options to publish a web server.

Summary: port mapping

In this group:

Container ports don't open to the outside by themselves; they are published with -p host:container.
The left side is the host, the right side the container; a host port can be published to only one place.
Several -p flags, ranges and /udp are supported.
-p 80 and -P pick a random host port; docker port shows the chosen one.
127.0.0.1: opens it only to local access; ports that aren't needed are not published at all.

docker run -d -p 80:80 -p 443:443 nginx
docker run -d -p 127.0.0.1:5432:5432 postgres:16

Exercise Web and a local database

Write two commands: start a container named web from nginx in the background, publishing ports 80 and 443 with the same numbers; start a container named db from postgres:16 in the background with POSTGRES_PASSWORD=gizli, publishing 5432 only on 127.0.0.1.

Show example solution

docker run -d --name web -p 80:80 -p 443:443 nginx
docker run -d --name db -e POSTGRES_PASSWORD=gizli -p 127.0.0.1:5432:5432 postgres:16

Test yourself

In docker run -p 8080:3000 img, which port must the application listen on inside the container?
- Both
- 3000
- 8080
- 80
Show answer

3000 — The right side is the container port.

Publish all EXPOSEd ports.

docker run -d ____ api:1.0

Show answer

docker run -d -P api:1.0

Match.

-p 8080:80

Fixed mapping
-P

Random, all EXPOSE
127.0.0.1:

Local binding
docker port

Show mappings

Next lesson: Data persistence

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