Ability to add multiple modbus hubs

OK, just got to test this as well. It works great. I can finally delete my second instance of Hass and run all in a single container. Thanks @PtP.

Here is the corrected custom_component modbus1.py:

"""
Support for Modbus.

For more details about this component, please refer to the documentation at
https://home-assistant.io/components/modbus/
"""
import logging
import threading

import voluptuous as vol

import homeassistant.helpers.config_validation as cv
from homeassistant.const import (
    EVENT_HOMEASSISTANT_START, EVENT_HOMEASSISTANT_STOP,
    CONF_HOST, CONF_METHOD, CONF_PORT, CONF_TYPE, CONF_TIMEOUT, ATTR_STATE)

DOMAIN = 'modbus1'

REQUIREMENTS = ['pymodbus==1.3.1']

# Type of network
CONF_BAUDRATE = 'baudrate'
CONF_BYTESIZE = 'bytesize'
CONF_STOPBITS = 'stopbits'
CONF_PARITY = 'parity'

SERIAL_SCHEMA = {
    vol.Required(CONF_BAUDRATE): cv.positive_int,
    vol.Required(CONF_BYTESIZE): vol.Any(5, 6, 7, 8),
    vol.Required(CONF_METHOD): vol.Any('rtu', 'ascii'),
    vol.Required(CONF_PORT): cv.string,
    vol.Required(CONF_PARITY): vol.Any('E', 'O', 'N'),
    vol.Required(CONF_STOPBITS): vol.Any(1, 2),
    vol.Required(CONF_TYPE): 'serial',
    vol.Optional(CONF_TIMEOUT, default=3): cv.socket_timeout,
}

ETHERNET_SCHEMA = {
    vol.Required(CONF_HOST): cv.string,
    vol.Required(CONF_PORT): cv.positive_int,
    vol.Required(CONF_TYPE): vol.Any('tcp', 'udp', 'rtuovertcp'),
    vol.Optional(CONF_TIMEOUT, default=3): cv.socket_timeout,
}


CONFIG_SCHEMA = vol.Schema({
    DOMAIN: vol.Any(SERIAL_SCHEMA, ETHERNET_SCHEMA)
}, extra=vol.ALLOW_EXTRA)


_LOGGER = logging.getLogger(__name__)

SERVICE_WRITE_REGISTER = 'write_register'
SERVICE_WRITE_COIL = 'write_coil'

ATTR_ADDRESS = 'address'
ATTR_UNIT = 'unit'
ATTR_VALUE = 'value'

SERVICE_WRITE_REGISTER_SCHEMA = vol.Schema({
    vol.Required(ATTR_UNIT): cv.positive_int,
    vol.Required(ATTR_ADDRESS): cv.positive_int,
    vol.Required(ATTR_VALUE): vol.All(cv.ensure_list, [cv.positive_int])
})

SERVICE_WRITE_COIL_SCHEMA = vol.Schema({
    vol.Required(ATTR_UNIT): cv.positive_int,
    vol.Required(ATTR_ADDRESS): cv.positive_int,
    vol.Required(ATTR_STATE): cv.boolean
})

HUB = None


def setup(hass, config):
    """Set up Modbus component."""
    # Modbus connection type
    client_type = config[DOMAIN][CONF_TYPE]

    # Connect to Modbus network
    # pylint: disable=import-error

    if client_type == 'serial':
        from pymodbus.client.sync import ModbusSerialClient as ModbusClient
        client = ModbusClient(method=config[DOMAIN][CONF_METHOD],
                              port=config[DOMAIN][CONF_PORT],
                              baudrate=config[DOMAIN][CONF_BAUDRATE],
                              stopbits=config[DOMAIN][CONF_STOPBITS],
                              bytesize=config[DOMAIN][CONF_BYTESIZE],
                              parity=config[DOMAIN][CONF_PARITY],
                              timeout=config[DOMAIN][CONF_TIMEOUT])
    elif client_type == 'rtuovertcp':
        from pymodbus.client.sync import ModbusTcpClient as ModbusClient
        from pymodbus.transaction import ModbusRtuFramer as ModbusFramer
        client = ModbusClient(host=config[DOMAIN][CONF_HOST],
                              port=config[DOMAIN][CONF_PORT],
                              framer=ModbusFramer,
                              timeout=config[DOMAIN][CONF_TIMEOUT])
    elif client_type == 'tcp':
        from pymodbus.client.sync import ModbusTcpClient as ModbusClient
        client = ModbusClient(host=config[DOMAIN][CONF_HOST],
                              port=config[DOMAIN][CONF_PORT],
                              timeout=config[DOMAIN][CONF_TIMEOUT])
    elif client_type == 'udp':
        from pymodbus.client.sync import ModbusUdpClient as ModbusClient
        client = ModbusClient(host=config[DOMAIN][CONF_HOST],
                              port=config[DOMAIN][CONF_PORT],
                              timeout=config[DOMAIN][CONF_TIMEOUT])
    else:
        return False

    global HUB
    HUB = ModbusHub(client)

    def stop_modbus(event):
        """Stop Modbus service."""
        HUB.close()

    def start_modbus(event):
        """Start Modbus service."""
        HUB.connect()
        hass.bus.listen_once(EVENT_HOMEASSISTANT_STOP, stop_modbus)

        # Register services for modbus
        hass.services.register(
            DOMAIN, SERVICE_WRITE_REGISTER, write_register,
            schema=SERVICE_WRITE_REGISTER_SCHEMA)
        hass.services.register(
            DOMAIN, SERVICE_WRITE_COIL, write_coil,
            schema=SERVICE_WRITE_COIL_SCHEMA)

    def write_register(service):
        """Write modbus registers."""
        unit = int(float(service.data.get(ATTR_UNIT)))
        address = int(float(service.data.get(ATTR_ADDRESS)))
        value = service.data.get(ATTR_VALUE)
        if isinstance(value, list):
            HUB.write_registers(
                unit,
                address,
                [int(float(i)) for i in value])
        else:
            HUB.write_register(
                unit,
                address,
                int(float(value)))

    def write_coil(service):
        """Write modbus coil."""
        unit = service.data.get(ATTR_UNIT)
        address = service.data.get(ATTR_ADDRESS)
        state = service.data.get(ATTR_STATE)
        HUB.write_coil(unit, address, state)

    hass.bus.listen_once(EVENT_HOMEASSISTANT_START, start_modbus)

    return True


class ModbusHub(object):
    """Thread safe wrapper class for pymodbus."""

    def __init__(self, modbus_client):
        """Initialize the modbus hub."""
        self._client = modbus_client
        self._lock = threading.Lock()

    def close(self):
        """Disconnect client."""
        with self._lock:
            self._client.close()

    def connect(self):
        """Connect client."""
        with self._lock:
            self._client.connect()

    def read_coils(self, unit, address, count):
        """Read coils."""
        with self._lock:
            kwargs = {'unit': unit} if unit else {}
            return self._client.read_coils(
                address,
                count,
                **kwargs)

    def read_input_registers(self, unit, address, count):
        """Read input registers."""
        with self._lock:
            kwargs = {'unit': unit} if unit else {}
            return self._client.read_input_registers(
                address,
                count,
                **kwargs)

    def read_holding_registers(self, unit, address, count):
        """Read holding registers."""
        with self._lock:
            kwargs = {'unit': unit} if unit else {}
            return self._client.read_holding_registers(
                address,
                count,
                **kwargs)

    def write_coil(self, unit, address, value):
        """Write coil."""
        with self._lock:
            kwargs = {'unit': unit} if unit else {}
            self._client.write_coil(
                address,
                value,
                **kwargs)

    def write_register(self, unit, address, value):
        """Write register."""
        with self._lock:
            kwargs = {'unit': unit} if unit else {}
            self._client.write_register(
                address,
                value,
                **kwargs)

    def write_registers(self, unit, address, values):
        """Write registers."""
        with self._lock:
            kwargs = {'unit': unit} if unit else {}
            self._client.write_registers(
                address,
                values,
                **kwargs)

And the custom_component/sensor modbus1.py:

"""
Support for Modbus Register sensors.

For more details about this platform, please refer to the documentation at
https://home-assistant.io/components/sensor.modbus/
"""
import logging
import struct

import voluptuous as vol

import custom_components.modbus1 as modbus
from homeassistant.const import (
    CONF_NAME, CONF_OFFSET, CONF_UNIT_OF_MEASUREMENT, CONF_SLAVE,
    CONF_STRUCTURE)
from homeassistant.helpers.entity import Entity
from homeassistant.helpers import config_validation as cv
from homeassistant.components.sensor import PLATFORM_SCHEMA

_LOGGER = logging.getLogger(__name__)

DEPENDENCIES = ['modbus1']

CONF_COUNT = 'count'
CONF_REVERSE_ORDER = 'reverse_order'
CONF_PRECISION = 'precision'
CONF_REGISTER = 'register'
CONF_REGISTERS = 'registers'
CONF_SCALE = 'scale'
CONF_DATA_TYPE = 'data_type'
CONF_REGISTER_TYPE = 'register_type'

REGISTER_TYPE_HOLDING = 'holding'
REGISTER_TYPE_INPUT = 'input'

DATA_TYPE_INT = 'int'
DATA_TYPE_UINT = 'uint'
DATA_TYPE_FLOAT = 'float'
DATA_TYPE_CUSTOM = 'custom'

PLATFORM_SCHEMA = PLATFORM_SCHEMA.extend({
    vol.Required(CONF_REGISTERS): [{
        vol.Required(CONF_NAME): cv.string,
        vol.Required(CONF_REGISTER): cv.positive_int,
        vol.Optional(CONF_REGISTER_TYPE, default=REGISTER_TYPE_HOLDING):
            vol.In([REGISTER_TYPE_HOLDING, REGISTER_TYPE_INPUT]),
        vol.Optional(CONF_COUNT, default=1): cv.positive_int,
        vol.Optional(CONF_REVERSE_ORDER, default=False): cv.boolean,
        vol.Optional(CONF_OFFSET, default=0): vol.Coerce(float),
        vol.Optional(CONF_PRECISION, default=0): cv.positive_int,
        vol.Optional(CONF_SCALE, default=1): vol.Coerce(float),
        vol.Optional(CONF_SLAVE): cv.positive_int,
        vol.Optional(CONF_DATA_TYPE, default=DATA_TYPE_INT):
            vol.In([DATA_TYPE_INT, DATA_TYPE_UINT, DATA_TYPE_FLOAT,
                    DATA_TYPE_CUSTOM]),
        vol.Optional(CONF_STRUCTURE): cv.string,
        vol.Optional(CONF_UNIT_OF_MEASUREMENT): cv.string
    }]
})


def setup_platform(hass, config, add_devices, discovery_info=None):
    """Set up the Modbus sensors."""
    sensors = []
    data_types = {DATA_TYPE_INT: {1: 'h', 2: 'i', 4: 'q'}}
    data_types[DATA_TYPE_UINT] = {1: 'H', 2: 'I', 4: 'Q'}
    data_types[DATA_TYPE_FLOAT] = {1: 'e', 2: 'f', 4: 'd'}

    for register in config.get(CONF_REGISTERS):
        structure = '>i'
        if register.get(CONF_DATA_TYPE) != DATA_TYPE_CUSTOM:
            try:
                structure = '>{}'.format(data_types[
                    register.get(CONF_DATA_TYPE)][register.get(CONF_COUNT)])
            except KeyError:
                _LOGGER.error("Unable to detect data type for %s sensor, "
                              "try a custom type.", register.get(CONF_NAME))
                continue
        else:
            structure = register.get(CONF_STRUCTURE)

        try:
            size = struct.calcsize(structure)
        except struct.error as err:
            _LOGGER.error(
                "Error in sensor %s structure: %s",
                register.get(CONF_NAME), err)
            continue

        if register.get(CONF_COUNT) * 2 != size:
            _LOGGER.error(
                "Structure size (%d bytes) mismatch registers count "
                "(%d words)", size, register.get(CONF_COUNT))
            continue

        sensors.append(ModbusRegisterSensor(
            register.get(CONF_NAME),
            register.get(CONF_SLAVE),
            register.get(CONF_REGISTER),
            register.get(CONF_REGISTER_TYPE),
            register.get(CONF_UNIT_OF_MEASUREMENT),
            register.get(CONF_COUNT),
            register.get(CONF_REVERSE_ORDER),
            register.get(CONF_SCALE),
            register.get(CONF_OFFSET),
            structure,
            register.get(CONF_PRECISION)))

    if not sensors:
        return False
    add_devices(sensors)


class ModbusRegisterSensor(Entity):
    """Modbus register sensor."""

    def __init__(self, name, slave, register, register_type,
                 unit_of_measurement, count, reverse_order, scale, offset,
                 structure, precision):
        """Initialize the modbus register sensor."""
        self._name = name
        self._slave = int(slave) if slave else None
        self._register = int(register)
        self._register_type = register_type
        self._unit_of_measurement = unit_of_measurement
        self._count = int(count)
        self._reverse_order = reverse_order
        self._scale = scale
        self._offset = offset
        self._precision = precision
        self._structure = structure
        self._value = None

    @property
    def state(self):
        """Return the state of the sensor."""
        return self._value

    @property
    def name(self):
        """Return the name of the sensor."""
        return self._name

    @property
    def unit_of_measurement(self):
        """Return the unit of measurement."""
        return self._unit_of_measurement

    def update(self):
        """Update the state of the sensor."""
        if self._register_type == REGISTER_TYPE_INPUT:
            result = modbus.HUB.read_input_registers(
                self._slave,
                self._register,
                self._count)
        else:
            result = modbus.HUB.read_holding_registers(
                self._slave,
                self._register,
                self._count)
        val = 0

        try:
            registers = result.registers
            if self._reverse_order:
                registers.reverse()
        except AttributeError:
            _LOGGER.error("No response from modbus slave %s, register %s",
                          self._slave, self._register)
            return
        byte_string = b''.join(
            [x.to_bytes(2, byteorder='big') for x in registers]
        )
        val = struct.unpack(self._structure, byte_string)[0]
        self._value = format(
            self._scale * val + self._offset, '.{}f'.format(self._precision))

Let us know when you post on GitHub so we can support the fixed implementation of multiple modbus or to update the Home Assistant documentation, if we can only add a modbus1.py!