Publishing ports
- Docker & Kubernetes course
- Beginner
- Lesson 76/82
- 4 min
Learn to publish ports on a network.
Port publishing and internal traffic
Containers on the same network reach each other directly through the container port; publishing a port is only for the host and the outside world. That is why the container port, not the host port, is used in connection addresses:
docker run -d --name db --network arka -p 15432:5432 postgres:16
# from the host: psql -h localhost -p 15432
# api on the arka network: postgresql://db:5432/app (not 15432!)The reverse proxy pattern
A common layout: only a reverse proxy (nginx, Traefik, Caddy) publishes 80/443 and forwards requests to services inside the network by service name. The application and database publish no ports:
# nginx.conf
location /api/ {
proxy_pass http://api:8000/;
}
docker run -d --name vekil --network on -p 80:80 -v "$PWD/nginx.conf":/etc/nginx/conf.d/default.conf:ro nginxPractice A proxied setup
Write two commands: start a container named api from api:1.0 in the background on the on network without publishing ports; start a container named vekil from nginx in the background on the on network, mapping 80 to 80 and mounting "$PWD/nginx.conf" read-only at /etc/nginx/conf.d/default.conf.
Starter code
# buraya yazSample solution
docker run -d --name api --network on api:1.0
docker run -d --name vekil --network on -p 80:80 -v "$PWD/nginx.conf":/etc/nginx/conf.d/default.conf:ro nginxExpected output
091a2b3c4d5e 1a2b3c4d5e6f
Questions and answers
Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.
1 If db is published with -p 15432:5432, which address should api on the same network connect to?
- db:5432 Correct answer
- db:15432
- localhost:15432
- localhost:5432
Explanation: Inside a container, localhost is the container itself.
2 Forward the request to the api service.
location /api/ {
proxy_pass http://____:8000/;
}location /api/ {
proxy_pass http://api:8000/;
}Explanation: The service name on the network is the DNS name.
3 Match.
| Term | Meaning |
|---|---|
container port |
In-network traffic |
published port |
Host and outside world |
reverse proxy |
Single entry point |
localhost (inside the container) |
The container itself |