docker-compose nested values sample

docker-compose.yml

version: '3.5'

x-env: &env-common
  COMMON_VALUE: "my-common-value"

x-service: &service-common
  network_mode: host
  environment:
    <<: *env-common

services:

  env:
    <<: *service-common
    image: "alpine"
    command: "env"

  env-with-custom:
    <<: *service-common
    image: "alpine"
    command: "env"
    environment:
      <<: *env-common
      CUSTOM_VALUE: my-custom-value