Docker - send http request from one container to another - reactjs

Question

I cannot send an HTTP request to backend container when I'm running app on AWS server production. However, when I'm running app locally I can make requests to backend just fine. For making requests I use fetch:
fetch('http://localhost:8000/something')
Here is how project structure looks like:
.
├── docker-compose.yml
|
├── backend
│   ├── Dockerfile
│   └── server.js
|
└── frontend
├── Dockerfile
├── package.json
├── public
│   └── index.html
└── src
   ├── components
   ├── data
   ├── index.js
   ├── routes.js
   ├── static
   ├── tests
   └── views
docker-compose.yml:
version: '3'
services:
frontend:
build:
context: .
dockerfile: frontend/Dockerfile
volumes:
- ./frontend:/frontend
ports:
- "80:5000"
links:
- backend
backend:
build:
context: .
dockerfile: backend/Dockerfile
volumes:
- ./backend:/backend
ports:
- "8000:8000"
Dockerfile in frontend:
FROM node:latest
RUN mkdir -p /frontend
WORKDIR /frontend
ADD . /frontend
VOLUME ["/frontend"]
EXPOSE 5000
CMD yarn && yarn build && yarn global add serve && serve -s build
Dockerfile in backend:
FROM node:latest
RUN mkdir -p /backend
WORKDIR /backend
ADD . /backend
VOLUME ["/backend"]
EXPOSE 8000
CMD yarn && yarn start
Can someone explain me what is wrong with my config? I'm very confused, because it works without any issues locally.

Answer 1

TLDR: Need to change the frontend code to call the current host instead of 'localhost'
The problem is your app is saying 'hey localhost' instead of 'hey VPS ip', when visiting from YOUR browser. You need to edit your frontend code to visit the current host you're visiting. That's why you're receiving a request on YOUR localhost server.
Instead of fetch("http:///localhost:8000/something") change it to fetch("http://"+location.host+":8000") (There are better ways, this gets it done).
Also note docker containers are a little different in terms of networking as well. A docker container doesn't really have a concept of 'localhost' the same way non docker container apps do. You have to use the VPS's IP/Local IP when making the call from server to server. A trick I use is to use docker's default docker0 bridge 172.17.0.1.
I tend to use networks over 'links' and actually cant comment fully on it, but when containers were on the same docker network, you could access the other container by using the container's name. This only works for server side code however, ie: node.js server -> node.js server/mongo db. Example mongodb connection would be mongodb://mongo_server:27017/mydatabase and mongo_server would resolve to the container's IP.
Another thing you'll possibly encounter when attempting to use the IP is your firewall, you would have to allow that particular ip/port in through your firewall as well.