I’m doing a project that uses docker to create an app to send SMS via Twilio.
The project is build using Rails.
Right now, my docker-compose build 3 containers: Postgres, Prometheus and web-service.

Everything seems to work correctly, and I can access localhost:3000 (Web service to send SMS), localhost:9090 (prometheus, to see logs and stuff).

The issue is, my prometheus container is not accessing localhost:3000. I got 403 access denied, when trying on browser, inside prometheus app, and via internal prometheus docker shell – with wget pointing to localhost:3000

Dockerfile:

FROM ruby:2.7.5

# Update and install dependencies
RUN apt-get update -qq && apt-get install -y nodejs postgresql-client curl

# Install Yarn
RUN curl -sS https://dl.yarnpkg.com/debian/pubkey.gpg | apt-key add - 
    && echo "deb https://dl.yarnpkg.com/debian/ stable main" | tee /etc/apt/sources.list.d/yarn.list 
    && apt-get update && apt-get install -y yarn

# Clean up
RUN apt-get clean && rm -rf /var/lib/apt/lists/*

# Set the working directory inside the container
WORKDIR /app

# Add the `bin/` directory to the PATH
ENV PATH /app/bin:$PATH

# Copy the Gemfile and Gemfile.lock into the container
COPY Gemfile Gemfile.lock ./

# Install the correct version of Bundler
RUN gem install bundler:2.4.21

# Install gems
RUN bundle install --binstubs --jobs 20 --retry 5

# Copy the main application
COPY . /app

# Expose port 3000 to the outside
EXPOSE 3000

# Configure the main process to run when running the image
CMD ["sh", "-c", "bundle exec rails db:migrate && rails server -b '0.0.0.0'"]

docker-compose.yml

services:
  db:
    image: postgres
    volumes:
      - postgres_data:/var/lib/postgresql/data
    environment:
      POSTGRES_PASSWORD: password
      POSTGRES_USER: postgres
      POSTGRES_DB: my_name_sms_service
    ports:
      - "5432:5432"
    networks:
      - skynet

  web:
    build: .
    command: bash -c "rm -f tmp/pids/server.pid && bundle exec rails db:migrate && bundle exec rails s -p 3000 -b '0.0.0.0'"
    volumes:
      - .:/app
    ports:
      - "3000:3000"
    depends_on:
      - db
    environment:
      DATABASE_URL: postgres://postgres:password@db/my_name_sms_service
      TWILIO_ACCOUNT_SID: secret_key
      TWILIO_AUTH_TOKEN: secret_key
      TWILIO_PHONE_NUMBER: secret_phone
    networks:
      - skynet

  prometheus:
    image: prom/prometheus
    volumes:
      - ./prometheus.yml:/etc/prometheus/prometheus.yml
    ports:
      - "9090:9090"
    networks:
      - skynet

networks:
  skynet:

volumes:
  postgres_data:

Here’s how it appears:

enter image description here

Any clue?

Tried several different configurations for Dockerfile and docker-compose.
Created a network so all containers share it.
tried to add bypasses inside metrics_controller:

protect_from_forgery with: :null_session
skip_before_action :verify_authenticity_token