Deployment Modes

The OPC UA Device Support module can be configured to link and deploy the low-level OPC UA SDK (either open62541 or Unified Automation UASDK) using different strategies. These strategies are referred to as Deployment Modes.

The deployment mode is controlled by setting the OPEN62541_DEPLOY_MODE or UASDK_DEPLOY_MODE variable in the CONFIG_SITE.local file of the Device Support module.

This only applies to shared (dynamic) linking, as static linking always linkes all required Device Support and low-level functionality directly into the IOC binary.

Supported Modes

The following four modes are supported:

SYSTEM

The shared libraries of the SDK are expected to be in a system-standard location (e.g., /usr/lib or /usr/local/lib). The build system uses these libraries, and they must be present on the target system at runtime.

This option is most appropriate when the SDK libraries can be installed using the target system’s package manager.

PROVIDED

The shared libraries of the SDK are located in a specific directory defined by OPEN62541_SHRLIB_DIR or UASDK_SHRLIB_DIR. These are used during the build, and the target system’s runtime environment (e.g., LD_LIBRARY_PATH on Linux or PATH on Windows) must be configured to find them.

This option is most appropriate when the SDK libraries are compiled from sources and deployed to the same location on the target system.

INSTALL

The shared libraries of the SDK are copied (installed) into the Device Support module’s own library/binary directory during the build process. This makes the module more self-contained as it carries its own copies of the required SDK libraries. Under Linux, this will also require to configure the target system’s runtime environment.

This option is most appropriate under Windows, where keeping the DLLs next to the binary is the best way to ensure that these will be the ones used when the binary is run.

EMBED

The static library of the SDK is used to directly link the required functions into the opcua shared library. The SDK code becomes an integral part of libopcua.so (on Linux) or opcua.dll (on Windows). Consequently, the original SDK libraries are not required on the target system.

This option simplifies deployment (no low-level library needed on the target) at the cost of possibly using more memory (as other OPC UA clients cannot share the SDK library).

Recommendations

The suggested Deployment Mode depends on the operating system and the desired linking strategy for the EPICS application.

Windows

On Windows, the recommendation depends on the linkage chosen for the EPICS application:

Safer Dynamic Linking: INSTALL is preferred. This helps avoid “DLL hell” by ensuring that the necessary dependency libraries are copied to the application’s binary directory.
Simplicity: EMBED can be used for simplicity, particularly when the OPC UA Device Support is the only component on the system using that specific low-level library.

Linux

On Linux, the recommendation depends on how the low-level library is managed on the system:

System Packages: Use SYSTEM when the low-level library has been installed using the system’s package manager (such as apt or yum).
Custom Location: Use PROVIDED when the low-level library is deployed in a specific, non-standard location.
Simplicity: EMBED can be used for simplicity, particularly when the OPC UA Device Support is the only component on the system using that specific low-level library.