version: '3'
services:
  container_1:
    image: image_2_name:tag
    ports:
     - host_port:container_port
    environment:
     - ENV_VAR_1=val1
     - ENV_VAR_2=val2 
  container_2:
    image: image_2_name:tag
    ports:
     - host_port:container_port
    environment:
     - ENV_VAR_1=val1