Prisma inside Docker container cannot connect to Postgres on host machine (Can't reach database server at "123:5432"), but psql works inside container

I’m deploying a Node.js + Prisma backend using Docker on my VPS.
PostgreSQL is NOT in Docker — it runs directly on the VPS host (Ubuntu).
My backend is running inside Docker using docker compose.

DB_USER=vloq

DB_PASSWORD=******

DB_HOST=host.docker.internal

DB_PORT=5432

DB_NAME=furnix-staging

DATABASE_URL="postgresql://${DB_USER}:${DB_PASSWORD}@${DB_HOST}:${DB_PORT}/${DB_NAME}"

Since the DB runs on the host machine, I correctly use

✅ What works

From inside the running Docker container, I can install PostgreSQL client and successfully connect:

docker exec -it furnix-backend sh

apk add postgresql-client

psql -h host.docker.internal -U vloq -d furnix-staging

❌ What fails

Prisma inside the backend container throws:

PrismaClientInitializationError:

Can't reach database server at `123:5432`

Important:
123 is NOT in my .env.
It looks like Prisma is reading an old or wrong DATABASE_URL.

Docker logs show:

Can't reach database server at `123:5432`

Even though .env says:

host.docker.internal

❓ What I suspect

• Docker image may be caching the old .env

• DATABASE_URL may not be passed correctly by docker-compose

• Prisma may not see environment variables correctly during runtime

• docker compose up -d --build does not reload .env

docker-compose.yml

services:
  furnix-backend:
    build: .
    container_name: furnix-backend
    restart: always
    ports:
      - "7778:7777"
    env_file:
      - .env
    environment:
      NODE_ENV: production
    command: ["node", "dist/server.js"]

✔️ What I already tried

• Rebuilt without cache:

  docker compose down

  docker compose build --no-cache

  docker compose up -d

  Verified .env on host — it is correct.

  Verified DB connectivity from inside container.

  Verified Prisma works locally.

❓ My Question

Why is Prisma inside the Docker container still trying to connect to:

123:5432

even though:

DB_HOST=host.docker.internal

is set correctly in .env, and psql from inside the container can connect successfully?

How can I ensure Docker / Prisma loads the correct .env so DATABASE_URL resolves properly?