args:

version: "3.9"
services:
  webapp:
    build:
      context: ./dir
      dockerfile: Dockerfile-alternate
      args:
        buildno: 1

See also

• docker-compose, docker-compose.yml: [services | volumes | networks | up | down | restart | logs | create | changelog | version | secrets | config | -v | -h | exec], docker-compose pull, Environment:, Docker-compose.yml examples, .env, release notes, expose: