Fail to obtain connection between two Docker containers - docker

Question

I have an application that is divided in 2 parts: Frontend and Backend. My Frontend is a React JS application and my backend is a Java Spring boot application. This project is running in Docker, and there's 3 containers: frontend, backend and db (database). My problem is that I can't make my front and send any request to my backend container. Below is my Docker configuration files:
Docker-compose:
version: "3"
services:
db:
image: postgres:9.6
container_name: db
ports:
- "5433:5432"
environment:
- POSTGRES_PASSWORD=123
- POSTGRES_USER=postgres
- POSTGRES_DB=test
backend:
build:
context: ./backend
dockerfile: Dockerfile
container_name: backend
ports:
- "8085:8085"
depends_on:
- db
frontend:
container_name: frontend
build:
context: ./frontend
dockerfile: Dockerfile
expose:
- "80"
ports:
- "80:80"
links:
- backend
depends_on:
- backend
Dockerfile frontend:
# Stage 0, "build-stage", based on Node.js, to build and compile the frontend
FROM node:8.12.0 as build-stage
WORKDIR /app
COPY package*.json /app/
RUN yarn
COPY ./ /app/
RUN yarn run build
# Stage 1, based on Nginx, to have only the compiled app, ready for production with Nginx
FROM nginx
RUN rm -rf /usr/share/nginx/html/*
COPY --from=build-stage /app/build/ /usr/share/nginx/html
# Copy the default nginx.conf provided by tiangolo/node-frontend
COPY --from=build-stage /app/nginx.conf /etc/nginx/conf.d/default.conf
Dockerfile backend:
FROM openjdk:8
ADD /build/libs/reurb-sj-13-11-19.jar reurb-sj-13-11-19.jar
EXPOSE 8085
ENTRYPOINT ["java", "-jar", "reurb-sj-13-11-19.jar", "--app.db.host=
Is Frontend I've tried to send requests to these Ip's:
localhost:8085
172.18.0.3:8085
172.18.0.3
0.0.0.0:8085
When I try to send a request from Frontend, it "starts" and waits for about 10 seconds, then it returns with an error. The weird part is that my request doesn't return with any status.
PS.: I've read all internet and everyone said to put EXPOSE, PORTS and the LINKS (inside docker-compose), I've tried but still doesn't work.

Answer 1

You need to connect to backend:8085.
--
You shouldn't be using IP's to connect to your services but rather the service name listed in your docker-compose file.
Note: If using localhost, that refers to frontend container itself. Usually 0.0.0.0 is used to bind to all IP's or represent any IP address rather than connecting to a specific IP.
So in your front-end code, you need to use backend as the hostname (E.g., backend:8085).
It looks like you have already linked your services so networking shouldn't be an issue. My advice is to always test within the container using something such as:
docker-compose exec frontend bash
# You may need to install packages
ping backend
telnet backend 8085

Answer 2

I think it is worth mentioning that link is legacy and eventually will be removed.
Source: https://docs.docker.com/network/links/
Unless you really need it, you should create custom network for your app. Good documentation is here: https://docs.docker.com/compose/compose-file/#networks
And example:
version: "3"
services:
db:
image: postgres:9.6
container_name: db
ports:
- "5433:5432"
environment:
- POSTGRES_PASSWORD=123
- POSTGRES_USER=postgres
- POSTGRES_DB=test
networks:
- new
backend:
build:
context: ./backend
dockerfile: Dockerfile
container_name: backend
ports:
- "8085:8085"
depends_on:
- db
networks:
- new
frontend:
container_name: frontend
build:
context: ./frontend
dockerfile: Dockerfile
expose:
- "80"
ports:
- "80:80"
networks:
- new
depends_on:
- backend
networks:
new: