How to increase max_connection in official postgreSQL 10.0 docker image

run this docker-compose.yml

version: '2'
services:
  postgres:
    image: postgres:10.3-alpine
    command: postgres -c 'max_connections=200'
    environment:
      POSTGRES_DB: pgdb
      POSTGRES_PASSWORD: postgres
      POSTGRES_USER: postgres
    stdin_open: true
    tty: true
    ports:
    - 5432:5432/tcp

It is as simple as (you just override the default CMD with postgres -N 500):

docker run -d --name db postgres:10 postgres -N 500

You can check it using:

docker run -it --rm --link db:db postgres psql -h db -U postgres

show max_connections;

max_connections 
-----------------
500
(1 row)