Docker | Google Cloud - Fails when react start - reactjs

Question

I'm trying to dockerize a MERN stack but when the time comes when react has to start, the container exit with status 0.
This is the log error:
This is the structure of my project:
- project
- server
- api
api.yml
server.js
Dockerfile
- www
app.yml
Dockerfile
docker-compose.yml
The www folder contains the starter files the will be generate from npx create-react-app www.
The content of server/Dockerfile is:
FROM node:latest
RUN mkdir -p /usr/server
WORKDIR /usr/server
RUN npm install -g nodemon
EXPOSE 3000
CMD [ "npm", "start" ]
the content of www/Dockerfile is:
FROM node:latest
RUN mkdir -p /usr/www/src/app
WORKDIR /usr/www/src/app
EXPOSE 3000
CMD [ "npm", "start" ]
and, in the end the content of docker-compose.yml is:
version: '3.7'
services:
mongodb:
image: mongo
ports:
- 27017:27017
api:
build: ./server/
ports:
- "6200:6200"
volumes:
- ./server:/usr/server
depends_on:
- mongodb
www:
build: ./www/
ports:
- 3000:3000
volumes:
- ./www:/usr/www/src/app
depends_on:
- api
Now, in the title I mention Google Cloud, because I tried to distribute the different "server" and "www" parts in my production environment. The distribution of server works correctly butwww fails with this error:
The errors that are generated by Docker and Google Cloud seem very similar or am I wrong? Could it be a reaction problem or am I wrong in both cases?
I also leave the contents of the app.yaml andapi.yaml files.
app.yaml
runtime: nodejs
env: flex
# Only for developing
manual_scaling:
instances: 1
resources:
cpu: 1
memory_gb: 0.5
disk_size_gb: 10
handlers:
- url: /.*
static_files: build/index.html
upload: build/index.html
- url: /
static_dir: build
The content of the api.yaml file is the same as that of app.yaml but without the handlers section.