.env

NGROK_AUTH=My_auth_token

docker-compose.yaml

version: '3.7'
services:
    nginx:
        # some stuff
 
    ngrok:
        image: 'wernight/ngrok:latest'
        command: ['ngrok', 'start', '--all', '-authtoken=${NGROK_AUTH:?}']
        ports:
            -
                published: '4040'
                target: '4040'
                protocol: 'tcp'
                mode: 'host'
        volumes:
            -
                type: 'bind'
                source: './ngrok.yml'
                target: '/home/ngrok/.ngrok2/ngrok.yml'
                consistency: 'delegated'
                read_only: true
        tty: true
        container_name: 'ngrok'

ngrok.yml

region: 'eu'
log: 'stdout'
web_addr: '0.0.0.0:4040'
tunnels:
    my_app:
        proto: 'http'
        addr: 'nginx:80'
        bind_tls: false