Change the port mapping to ${FRONTEND_PORT}:3000 so the container always uses 3000 internally but maps to a different host port.

backend/Dockerfile

@@ -10,5 +10,5 @@ WORKDIR /app
 COPY package*.json ./
 RUN npm ci --omit=dev
 COPY --from=base /app/dist ./dist
-EXPOSE 5001 
+EXPOSE 3001 
 CMD ["node", "dist/src/main.js"]

docker-compose.yml

@@ -47,6 +47,6 @@ services:
       UPLOAD_R2_WORKER_API: ${UPLOAD_R2_WORKER_API}
       R2_UPLOAD_API_KEY: ${R2_UPLOAD_API_KEY}
     ports:
-      - "${FRONTEND_PORT}:${FRONTEND_PORT}"
+      - "${FRONTEND_PORT}:3000"
     depends_on:
       - backend

frontend/Dockerfile

@@ -11,5 +11,5 @@ COPY package*.json ./
 RUN npm ci --omit=dev
 COPY --from=base /app/.next ./.next
 COPY --from=base /app/public ./public
-EXPOSE 5000
+EXPOSE 3000
 CMD ["npm", "start"]