Unpopular docker compose YAML template

docker-compose.yml

version: '3'

x-tpl-nginx-lb: &tpl-nginx-lb
  image: nginx:stable-alpine
  restart: unless-stopped
  expose: [ 80 ]
  entrypoint:
    - sh
    - -c
    - |
      cat << EOF > /etc/nginx/conf.d/default.conf
      map \$$http_upgrade \$$connection_upgrade {
        default upgrade;
        ''      close;
      }
      upstream backend {
        $$UPSTREAM_BACKEND
      }
      server  {
        listen 80;
        listen [::]:80;
        server_name _;
        location / {
          proxy_pass http://backend;
          proxy_set_header X-Infra-Forwarder-Host "$$HOSTNAME";
          proxy_set_header X-Infra-Forwarder-Request-ID \$$request_id;
          proxy_set_header X-Forwarded-Host \$$host;
          proxy_set_header X-Forwarded-For \$$proxy_add_x_forwarded_for;
          
          proxy_set_header X-Real-IP \$$remote_addr;
          proxy_set_header Host \$$host;
          proxy_set_header Upgrade \$$http_upgrade;
          proxy_set_header Connection \$$connection_upgrade;
          
          set_real_ip_from 192.168.60.0/24;
          set_real_ip_from 192.168.63.0/24;
          real_ip_header X-Real-IP;
          real_ip_recursive on;
        }
      }
      EOF
      /docker-entrypoint.sh "nginx" "-g" "daemon off;"



networks:
  infra-core:
    driver: bridge
    ipam:
      driver: default
      config:
        - subnet: 192.168.63.0/24
          gateway: 192.168.63.1
          

services:
  mimir-lb:
    <<: *tpl-nginx-lb
    environment:
      - |
        UPSTREAM_BACKEND=
        server mimir-1:8080;
        server mimir-2:8080;
    networks:
      - infra-core