Can ping but not wget between Docker containers - wordpress

Question

I am using docker-compose to set up a NextJS-app that fetches data from the Wordpress REST-API running in separate containers.
Problem is, I get ECONNREFUSED when I try to fetch or WGET the wordpress-container http://wordpress:8000 from the NextJS-container. I can ping wordpress:8000 without any problems.
If I use Postman or try to fetch the REST-API from another host (i.e. not the machine running docker-compose) using the public ip, it works perfectly.
I'm suspecting some docker configuration issue, but I'm quite lost as the pinging works but not the wget.
Anyone with an idea on what the culprit could be?
My docker-compose.yml:
version: '2'
services:
db:
image: mysql:5.7
volumes:
- db_data:/var/lib/mysql
restart: always
environment:
MYSQL_ROOT_PASSWORD: ***REMOVED***
MYSQL_DATABASE: ***REMOVED***
MYSQL_USER: ***REMOVED***
MYSQL_PASSWORD: ***REMOVED***
networks:
- back
wordpress:
depends_on:
- db
image: wordpress:latest
volumes:
- ./wp-content:/var/www/html/wp-content
ports:
- "8000:80"
restart: always
environment:
WORDPRESS_DB_HOST: db:3306
WORDPRESS_DB_USER: root
WORDPRESS_DB_PASSWORD: ***REMOVED****
networks:
- back
phpmyadmin:
depends_on:
- db
image: phpmyadmin/phpmyadmin
restart: always
ports:
- 8080:80
environment:
PMA_HOST: db
MYSQL_ROOT_PASSWORD: ***REMOVED***
networks:
- back
next-app:
depends_on:
- wordpress
build:
context: ./next-app
dockerfile: Dockerfile
volumes:
- './next-app:/usr/src/app'
- '/usr/src/app/node_modules'
ports:
- '80:3000'
networks:
- back
express-server:
build:
context: ./express-server
dockerfile: Dockerfile
ports:
- '3001:3001'
networks:
back:
driver: bridge
volumes:
db_data:

Answer 1

From inside the NextJS-container you need to use port 80. Port 8000 it's from your (host) machine. So use http://wordpress:80 from inside the docker containers.
ports:
- "8000:80"
In you docker-compose file just says: "Map my local (host machine) port 8000 to containers ports 80", but inside the docker network, it's still port 80
You can ping, because ping doesn't use ports. Ports that we are talking about are TCP/UDP ports, see https://en.wikipedia.org/wiki/Port_(computer_networking). But ping uses ICMP (Internet Control Message Protocol), which doesn't use ports at all, see https://en.wikipedia.org/wiki/Ping_(networking_utility)