Using a clean Ubuntu 20.04 install:

1. Production instructions at /frappe/bench#docker-installation:

.env:
    ERPNEXT_VERSION=edge
    FRAPPE_VERSION=edge
    MARIADB_HOST=db.host.com
    MYSQL_ROOT_PASSWORD=<snip>
    SITES=my.hostname.com
    [email protected]

Install:
    # docker-compose     --project-name sensible     -f installation/docker-compose-common.yml     -f installation/docker-compose-erpnext.yml     -f installation/docker-compose-networks.yml     --project-directory installation up -d
    WARNING: The MYSQL_ROOT_PASSWORD variable is not set. Defaulting to a blank string.
    WARNING: The ERPNEXT_VERSION variable is not set. Defaulting to a blank string.
    WARNING: The SITES variable is not set. Defaulting to a blank string.
    WARNING: The LETSENCRYPT_EMAIL variable is not set. Defaulting to a blank string.
    WARNING: The MARIADB_HOST variable is not set. Defaulting to a blank string.
    WARNING: The FRAPPE_VERSION variable is not set. Defaulting to a blank string.
    ERROR: no such image: frappe/erpnext-worker:: invalid reference format

2. Production instructions at /frappe/frappe_docker/blob/develop/docs/single-bench.md:

.env:
    ERPNEXT_VERSION=edge
    FRAPPE_VERSION=edge
    MARIADB_HOST=db.host.com
    MYSQL_ROOT_PASSWORD=<snip>
    SITES=`my.hostname.com`
    SITE_NAME=my.hostname.com
    [email protected]
    DB_ROOT_USER=root
    ADMIN_PASSWORD=<snip>
    INSTALL_APPS=erpnext
    ENTRYPOINT_LABEL=traefik.http.routers.erpnext-nginx.entrypoints=websecure
    CERT_RESOLVER_LABEL=traefik.http.routers.erpnext-nginx.tls.certresolver=myresolver
    HTTPS_REDIRECT_RULE_LABEL=traefik.http.routers.http-catchall.rule=hostregexp(`{host:.+}`)
    HTTPS_REDIRECT_ENTRYPOINT_LABEL=traefik.http.routers.http-catchall.entrypoints=web
    HTTPS_REDIRECT_MIDDLEWARE_LABEL=traefik.http.routers.http-catchall.middlewares=redirect-to-https
    HTTPS_USE_REDIRECT_MIDDLEWARE_LABEL=traefik.http.middlewares.redirect-to-https.redirectscheme.scheme=https

Install:
    root@db-b ~/frappe_docker # docker-compose --project-name sensible up -d
    Creating network "sensible_default" with the default driver
    Creating sensible_redis-queue_1    ... done
    Creating sensible_redis-cache_1    ... done
    Creating sensible_mariadb_1        ... done
    Creating sensible_redis-socketio_1         ... done
    Creating sensible_traefik_1                ... done
    Creating sensible_erpnext-python_1         ... done
    Creating sensible_erpnext-nginx_1  ... done
    Creating sensible_erpnext-worker-long_1    ... done
    Creating sensible_erpnext-worker-default_1 ... done
    Creating sensible_erpnext-schedule_1       ... done
    Creating sensible_erpnext-worker-short_1   ... done
    Creating sensible_frappe-socketio_1        ... done
    Creating sensible_site-creator_1           ... done

I had great hope, but attempting to load in a web browser returns "Internal Server Error".

Fine, try Easy Install (/frappe/bench#easy-install-script) - this docker stuff is all to new for this old Unix hand.  Let's go back to basics:

    # python3 install.py --production
    Logs are saved under /tmp/logs/easy-install__2020-11-10__05-10.log
    W: GPG error: http://ams2.mirrors.digitalocean.com/mariadb/repo/10.4/ubuntu focal InRelease: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY F1656F24C74CD1D8
    E: The repository 'http://ams2.mirrors.digitalocean.com/mariadb/repo/10.4/ubuntu focal InRelease' is not signed.
    Traceback (most recent call last):
      File "install.py", line 467, in <module>
        install_prerequisites()
      File "install.py", line 149, in install_prerequisites
        run_os_command({
      File "install.py", line 141, in run_os_command
        returncode = subprocess.check_call(command, shell=True, stdout=log_stream, stderr=sys.stderr)
      File "/usr/lib/python3.8/subprocess.py", line 364, in check_call
        raise CalledProcessError(retcode, cmd)
    subprocess.CalledProcessError: Command 'sudo apt-get update' returned non-zero exit status 100.

One almost gets the sense this is an attempt to get users to buy the cloud hosted service and keep OSS as a ruse.