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Configuration Builders

ConfigurationBuilders are a feature of the full .Net Framework that were introduced in .Net 4.7.1. You can read about the concept in this blog post. While the framework for executing configuration injection now exists in .Net as of 4.7.1 with that feature, the framework does not ship with any pre-made builders in box. The goal of this project is for Microsoft to provide a basic set of Configuration Builders that should make it easy for developers to leverage this feature in their apps. They are also intended to address some of the basic dynamic/non-local configuration needs of applications as they move into a container and cloud focused environment.

The set of builders produced here are styled as "Key/Value Config Builders." The architecture of ConfigurationBuilder in the framework is actually quite flexible and can be leveraged to handle a great number of unique situations. To keep things as easy and as broadly applicable as possible though, this project focuses on simple key/value scenarios.

For more information about Configuration Builders and the features and builders in this project in particular, please refer to the docs linked here:

V3 Updates:

  • ⚠️ Breaking Change - Expand mode is gone. It has been replaced by Token mode.#TODO verify link (and #enabled and #charmap link)
  • Utils.MapPath - This was somewhat broken in ASP.Net scenarios previously. It should now reliably go against Server.MapPath() in ASP.Net scenarios. It has also been updated to fall back against the directory of the config file being processed when resolving the app root in the case of a Configuration object being created by ConfigurationManager.OpenConfiguration* API's rather than being part of a fully-initialized runtime configuration stack.
  • Json use has migrated to use System.Text.Json instead of Newtonsoft.Json.
  • The Azure Config Builders have been updated to require a newer minimum version of Azure.Identity by default which allows for more methods of connecting to Azure, such as User-Assigned Managed Identity, or Client Certificate-based via environment variables. An overload named GetCredential has also been added for users who need something more custom than upgrading Azure.Identity can easily provide.
  • Added RecursionGuard to help detect and prevent situations where a ConfigurationBuilder accessing values from a ConfigurationSection other than the one which it is currently processing could result in stack overflow.
  • optional attribute is obsolete => enabled attribute which provides more versatility. (The optional attribute is still parsed and recognized in the absence of the newer enabled attribute, but builders should migrate to use the new attribute name when possible. Installation scripts should try to handle this automatically.)
  • Character Mapping - Some config builders have had an internal mapping of characters that might exist in keys in the config file but are illegal in keys at the source. As more scenarios come to light and individual prefrences are not always unanimous, V3 instead adds the charMap attribute to allow this character mapping to work with all KeyValueConfigBuilders and to be handled in an easily configurable manner.

V2 Updates:

  • Azure App Configuration Support - There is a new builder for drawing values from the new Azure App Configuration service.
  • ConfigBuilder Parameters from AppSettings - This has been one of the most asked for features of these config builders. With V2, it is now possible to read initialization parameters for config builders from appSettings. Read more about it here.
  • Lazy Initialization - As part of the work to enable pulling config parameters from appSettings, these key/value configuration builders now support a lazy initialization model. Things that must happen immediately can be left in the existing Initialize(name, config) method, or builders can leverage the new LazyInitialize(name, config) method for things that can happen just before retrieving values. All builders in this project have been updated to be lazy whenever possible.
  • Updateable Keys - Builders can now massage key names before inserting into config. The AzureKeyVaultConfigBuilder has been updated to use this feature to allow embedding 'version' tags in key names instead of applying a single 'version' tag to the builder. (Note: This is seperate from, and performed after prefix stripping.)
  • [[Obsolete]] This has been superceded by the enabled tag. (Base Optional Tag - The optional tag that some of the builders in this project employed in V1 has been moved into the base class and is now available on all key/value config builders.)
  • Escaping Expanded Values - It is possible to xml-escape inserted values in ExpandToken(as of V3) mode now using the new escapeExpandedValues attribute.
  • Section Handlers - This feature allows users to develop extensions that will apply key/value config to sections other than appSettings and connectionStrings if desired. Read more about this feature in the Section Handlers segment below.

How to contribute

Information on contributing to this repo is in the Contributing Guide.

Blog Posts

Announcing .NET 4.7.1 Tools for the Cloud
.Net Framework 4.7.1 ASP.NET and Configuration features
Modern Configuration for ASP.NET 4.7.1 with ConfigurationBuilders
Service-to-service authentication to Azure Key Vault using .NET