About opcua-lua
===============

``opcua-lua`` is Real Time Logic's OPC UA stack for Lua applications. It is
designed for systems where OPC UA connectivity must live close to the device,
gateway, web server, or embedded application instead of being isolated in a
large external service.

The stack supports the standard OPC UA Client/Server model and OPC UA PubSub
over MQTT. This means the same Lua application can expose an address space,
connect to another OPC UA server, publish selected values over MQTT, or consume
PubSub messages.


Why Lua
-------

Lua is small, embeddable, and fast to iterate with. In Real Time Logic products,
Lua also runs inside the Barracuda App Server environment used by `Mako Server
<https://makoserver.net/>`_, `Xedge
<https://realtimelogic.com/products/xedge/>`_, and `Xedge32
<https://realtimelogic.com/downloads/bas/ESP32/?bas=>`_. This makes it
possible to combine industrial automation, device logic, web APIs, dashboards,
and deployment scripts in one runtime.

The main benefits are:

**Lightweight embedded design**
  OPC UA functionality can run in constrained environments and edge devices
  without the footprint of many native desktop/server stacks.

**Rapid application development**
  Address-space logic, data sources, authentication callbacks, and PubSub
  workflows can be scripted and changed quickly.

**No native thread dependency**
  The client can use non-blocking cosocket mode, allowing asynchronous I/O
  without one operating-system thread per connection.

**Web and device integration**
  The same runtime can expose OPC UA data, serve web applications, and connect
  browser dashboards or cloud services.

**Client/Server and PubSub support**
  Applications can use browse/read/write/method calls when they need the OPC UA
  information model, and MQTT PubSub when they need message-based distribution.


Where it fits
-------------

``opcua-lua`` is a good fit when the OPC UA layer needs to be part of an
application instead of a separate industrial gateway process.

Common use cases include:

* Embedded devices that expose sensor or control data through OPC UA.
* Edge gateways that translate local device data into OPC UA and MQTT.
* `Mako Server <https://makoserver.net/>`_ applications that combine OPC UA
  with web APIs or browser-based operator views.
* `Xedge32 <https://realtimelogic.com/downloads/bas/ESP32/?bas=>`_
  applications that expose ESP32 device state through OPC UA.
* Prototypes where the information model, authentication, and data source logic
  are still changing.


What to read next
-----------------

Start with :doc:`opcua_overview` if OPC UA itself is new to you. Read
:doc:`pubsub/client_server_vs_pubsub` if you need to decide between a
browseable OPC UA server and MQTT PubSub messages.