Set network mode to achieve port binding at localhost.

docker-compose.yml

version: "3.5"
#$ docker run -d -p 6379:6379 redis
services:
  redis:
    image : redis
    ports:
      - "6379:6379"

  api_server:
    depends_on:
      - redis
    build:
      context: .
      dockerfile: api.Dockerfile
    environment:
      PORT: 8080
    ports:
      - "8080:8080"
    expose:
      - "8080"
    network_mode: host

  selam_server:
    build:
      context: .
      dockerfile: selam.Dockerfile
    environment:
      PORT: 15120
    ports:
      - "15120:15120/udp"
    expose:
      - "15120/udp"
    network_mode: host