An OPC UA Local Discovery Server (LDS) is a service that maintains a registry of the OPC UA servers available on the local network; clients can query it to find servers dynamically without knowing their URLs in advance.

The LDS workflow is simple: each server registers itself with the local LDS (typically on port 4840) and provides its URL, Application Description and supported Endpoints. The LDS keeps that list up to date through periodic heartbeats. A client then calls FindServers on the LDS to retrieve the registered server list, which enables a true plug-and-play experience where a new server on the network is immediately visible to all clients. Reference implementations exist in open source (open62541) and in commercial products (Unified Automation LDS).

Deploy an LDS on every site network even if you only have a handful of servers: it removes hard-coded URLs from your clients and dramatically simplifies day-2 operations such as server replacement or hostname changes.