Prometheus behind Nginx with CORS enabled

docker-compose.yml

version: '2'

services:
  prometheus:
    container_name: prometheus
    image: bitnami/prometheus:latest
    volumes:
      - ./prometheus.yml:/opt/bitnami/prometheus/conf/prometheus.yml
    ports:
      - "9090:9090"
    environment:
      FOO: 'bar'
      
  nginx:
    image: nginx:latest
    container_name: nginx
    volumes:
      - ./reverse_proxy.conf:/etc/nginx/conf.d/default.conf
    ports:
      - "9091:9091"
    links:
     - prometheus

prometheus.yml

# Just the demo prometheus config file that scrapes itself
global:
  scrape_interval:     15s # By default, scrape targets every 15 seconds.

  # Attach these labels to any time series or alerts when communicating with
  # external systems (federation, remote storage, Alertmanager).
  external_labels:
    monitor: 'codelab-monitor'

# A scrape configuration containing exactly one endpoint to scrape:
# Here it's Prometheus itself.
scrape_configs:
  # The job name is added as a label `job=<job_name>` to any timeseries scraped from this config.
  - job_name: 'prometheus'

    # Override the global default and scrape targets from this job every 5 seconds.
    scrape_interval: 5s

    static_configs:
      - targets: ['localhost:9090']

reverse_proxy.conf

server {
  listen 9091;
  server_name nginx;

  add_header 'Access-Control-Allow-Origin' 'http://localhost:1234';
  add_header 'Access-Control-Allow-Credentials' 'true';
  add_header 'Access-Control-Allow-Headers' 'Authorization,Accept,Origin,DNT,X-CustomHeader,Keep-Alive,User-Agent,X-Requested-With,If-Modified-Since,Cache-Control,Content-Type,Content-Range,Range';
  add_header 'Access-Control-Allow-Methods' 'GET,POST,OPTIONS,PUT,DELETE,PATCH';

  location / {
    proxy_hide_header 'Access-Control-Allow-Origin';
    proxy_pass http://prometheus:9090/;
  }
}