High-Level Intrinsic Configuration

Introduction

Many parameters of the software can be configured externally, without you having to write a specific code for it. The external configuration can be provided by multiple means, e.g. settings file (such as appsettings.json), environment variables, or Azure App configuration, and the functionality for it is already built-in to the components. This feature belongs to High-Level Configuration, and allows tweaking of component parameters for experiments, testing, and in production. Its main benefit is that the component parameters can be changed without somebody having to implement the code for it first, and/or without having to change and rebuild the application (which may come really handy if rebuilding the application is not an option for you, e.g. in many restricted production environments).

Where the configuration is read from (the "configuration providers") is determined by the default settings for your application host. For the usual hosts, these defaults are described here:

• In ASP.NET Core: Configuration in ASP.NET Core (Microsoft).
• In .NET console apps: Configuration in .NET (Microsoft).

Since this is a standard mechanism used by software libraries and applications, you will be able to place the configuration settings for QuickOPC component alongside with configuration settings for other parts of the software.

By far, the most commonly used configuration provider will probably the JSON configuration provider, and you will place your configuration data into the appsettings.json or appsettings.Environment.json file (e.g. appsettings.Production.json).

Where is this used?

For example:

• Intrinsic Component Configuration

Error Handling

All errors that occur when the components read their parameters using the intrinsic configuration mechanism are silently ignored. This behavior was chosen because the reading of the configuration happens at time that is generally unpredictable to the developers (such as inside the static constructors of the components), and exceptions thrown at unpredictable place would have potential to crash the application. When an error occurs, the configuration may be read just partially.

Changing the Configuration Providers

If your application requires a set of configuration providers different from the default, you can configure them differently through IHostBuilder interface by accessing the result value of StaticHost.GetHostBuilder() (StaticHost is in the OpcLabs.BaseLib.Extensions.Hosting namespace).

Of course, changing the configuration providers *does* require a code change; the configuration providers cannot be changed externally on an application that is already built.

Some applications built with QuickOPC already add configuration providers over those that are available by default. For example, the OpcCmd Utility adds the INI and XML configuration providers, and you can therefore use configuration files like these in the examples below with the OpcCmd utility.

Example: Adding and using the INI configuration provider

For example, to support a possibility to configure component parameters by key pairs from INI files, reference the Microsoft.Extensions.Configurations.Ini NuGet package, and add the following code at the beginning of your program:

StaticHost.GetHostBuilder().ConfigureAppConfiguration((hostingContext, config) =>
{
    IHostEnvironment hostEnvironment = hostingContext.HostingEnvironment;
    config
        .AddIniFile("appsettings.ini", optional: true, reloadOnChange: false)
        .AddIniFile($"appsettings.{hostEnvironment.EnvironmentName}.ini",
            optional: true, reloadOnChange: false);
});

The contents of the INI file which corresponds to the JSON example given earlier is as follows:

[OpcLabs.EasyOpc.UA.EasyUAClient:InstanceParameters:GdsEndpointDescriptor]
UrlString="opc.tcp://opcua.demo-this.com:58810/GlobalDiscoveryServer"

Example: Adding and using the XML configuration provider

For example, to support a possibility to configure component parameters by elements read from XML files, reference the Microsoft.Extensions.Configurations.Xml NuGet package, and add the following code at the beginning of your program:

StaticHost.GetHostBuilder().ConfigureAppConfiguration((hostingContext, config) =>
{
    IHostEnvironment hostEnvironment = hostingContext.HostingEnvironment;
    config
        .AddXmlFile("appsettings.xml", optional: true, reloadOnChange: false)
        .AddXmlFile($"appsettings.{hostEnvironment.EnvironmentName}.xml",
            optional: true, reloadOnChange: false);
});

The contents of the XML file which corresponds to the JSON example given earlier is as follows:

<?xml version="1.0" encoding="utf-8" ?>
<configuration>
  <OpcLabs.EasyOpc.UA.EasyUAClient>
    <InstanceParameters>
      <GdsEndpointDescriptor>
        <UrlString>opc.tcp://opcua.demo-this.com:58810/GlobalDiscoveryServer</UrlString>
      </GdsEndpointDescriptor>
    </InstanceParameters>
  </OpcLabs.EasyOpc.UA.EasyUAClient>
</configuration>