Docker Multi-container connection with docker compose - node.js

Question

I am trying to create a composition where two or more docker service can connect to each other in some way.
Here is my composition.
# docker-compose.yaml
version: "3.9"
services:
database:
image: "strapi-postgres:test"
restart: "always"
ports:
- "5435:5432"
project:
image: "strapi-project:test"
command: sh -c "yarn start"
restart: always
ports:
- "1337:1337"
env_file: ".env.project"
depends_on:
- "database"
links:
- "database"
Services
database
This is using a Image that is made with of Official Postgres Image.
Here is Dockerfile
FROM postgres:alpine
ENV POSTGRES_USER="root"
ENV POSTGRES_PASSWORD="password"
ENV POSTGRES_DB="strapi-postgres"
and using the default exposed port 5432 and forwarding to 5435 as defined in the Composition.
So the database service starts at some IPAddress that can be found using docker inspect.
project
This is a Image running a node application(strapi project configured to use postgres database).
Here is Dockerfile
FROM node:lts-alpine
WORKDIR /project
ADD package*.json .
ADD yarn.lock .
RUN npm install
COPY . .
RUN npm run build
EXPOSE 1337
and I am builing the Image using docker build. That gives me an Image with No Foreground Process.
Problems
When I was running the composition, the strapi-project container Exits with Error Code(0).
Solution: So I added command yarn start to run the Foreground Process.
As the project Starts it could not connect to database since it is trying to connect to 127.0.0.1:5432 (5432 since it should try to connect to the container port of database service and not 5435). This is not possible since this tries to connect to port 5432 inside the container strapi-project, which is not open for any process.
Solution: So I used the IPAddress that is found from the docker inspect and used that in a .env.project and passed this file to the project service of the Composition.
For Every docker compose up there is a incremental pattern(n'th time 172.17.0.2, n+1'th time 172.18.0.2, and so on) for the IPAddress of the Composition. So Everytime I run composition I need to edit the .env.project.
All of these are some hacky way to patch them together. I want some way to Create the Postgres database service to start first and then project to configure, connect, and to the database, start automatically.
Suggest me any edits, or other ways to configure them.

Answer 1

You've forgotten to put the CMD in your Dockerfile, which is why you get the "exited (0)" status when you try to run the container.
FROM node:lts-alpine
...
CMD yarn start
Compose automatically creates a Docker network and each service is accessible using its Compose container name as a host name. You never need to know the container-internal IP addresses and you pretty much never need to run docker inspect. (Other answers might suggest manually creating networks: or overriding container_name: and these are also unnecessary.)
You don't show where you set the database host name for your application, but an environment: variable is a common choice. If your database library doesn't already honor the standard PostgreSQL environment variables then you can reference them in code like process.env.PGHOST. Note that the host name will be different running inside a container vs. in your normal plain-Node development environment.
A complete Compose file might look like
version: "3.8"
services:
database:
image: "strapi-postgres:test"
restart: "always"
ports:
- "5435:5432"
project:
image: "strapi-project:test"
restart: always
ports:
- "1337:1337"
environment:
- PGHOST=database
env_file: ".env.project"
depends_on:
- "database"