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    .NET (server-side) SDK 5.x to 6.0 migration guide

    Read time: 10 minutes
    Last edited: Dec 07, 2022


    This topic explains how to adapt code that currently uses a 5.x version of the .NET server-side SDK to use version 6.0 or later.

    Before you migrate to 6.0, update to the latest 5.x version. Many of the changes that are mandatory in 6.0 were originally added in a 5.x version and made optional to use.

    If you update to the latest 5.x version, deprecation warnings appear in areas of your code that need to be changed for 6.0. You can then update them while still using 5.x, rather than migrating everything simultaneously.

    To learn more about updating to the latest 5.x version, visit the SDK's GitHub repository.

    Identifying .NET platforms for the 6.0 SDK

    The 6.x version of the SDK is compatible with the following .NET platform versions:

    • .NET 5.0 and higher.
    • .NET Framework 4.5.2 and higher.
    • .NET Core 2.1 and higher.
    • Any other runtime that supports the .NET Standard 2.0 API. However, even though Xamarin is compatible with .NET Standard 2.0, this SDK is not intended to be used with Xamarin. Use the client-side .NET SDK instead.

    LaunchDarkly no longer supports older .NET target frameworks, including .NET Standard 1.6, as is documented in the End of Life policy.

    There are some features that are only available in specific platform versions:

    The .NET build tools automatically load the most appropriate build of the SDK for whatever platform your application or library is targeted to.

    Using updated namespaces

    The namespace convention has changed. Instead of LaunchDarkly.Client, the main namespaces are now LaunchDarkly.Sdk and LaunchDarkly.Sdk.Server. Most of the class names have not changed, so you may be able to fix your using statements with a find and replace.

    Package names including the word "client" were confusing, because even though this library is a service client that makes requests to the LaunchDarkly service, we built it to use in a server-side context. Types that are specific to this server-side implementation are now in LaunchDarkly.Sdk.Server.

    The base LaunchDarkly.Sdk package contains types that are not specific to server-side .NET. They also exist in the client-side .NET SDK. When you view the SDK source code, notice that the base .Sdk namespace is implemented in the dotnet-sdk-common repository rather than dotnet-server-sdk.

    To learn more about the differences between SDKs, read Client-side and server-side SDKs.

    The full namespace schema is as follows:

    • Launchdarkly.Sdk

      • Provides: User, IUserBuilder, LdValue, EvaluationDetail, EvaluationReason
    • Launchdarkly.Sdk.Json

    • LaunchDarkly.Sdk.Server

      • Provides: Components, Configuration, LdClient, FeatureFlagsState
    • LaunchDarkly.Sdk.Server.Interfaces

      • Provides: types like IDataStore that are only used if you are writing a custom component. These were formerly in Launchdarkly.Client, so moving them makes the API much less cluttered.
      • It also provides interfaces like IFlagTracker that are available through LdClient, but are less commonly used.
    • LaunchDarkly.Sdk.Server.Integrations

      • Provides: the same types that were in Launchdarkly.Client.Integrations (added in 5.14.0), such as StreamingDataSourceBuilder. These are for configuring how the SDK connects with LaunchDarkly or other external services.

    Understanding changes to SDK configuration

    .NET SDK 5.14.0 added newer ways to use Configuration. Starting in version 6.0, those ways are mandatory. They are the only way to use Configuration.

    Instead of having many unrelated properties, each with their own ConfigurationBuilder method, most of the properties are now grouped into areas of functionality, each of which has its own builder class that is only available if you are using that functionality. For instance, if you use streaming mode, there are options you can set to control streaming mode, and if you use polling mode, you use a different builder that does not have the streaming options. Similarly, if you have disabled analytics events, the event-related options are not accessible.

    The basic areas of functionality are "data source" (polling, streaming, or file data), "data store" (memory or database), events, and networking.

    If your code already uses the newer model, you may only need to change the package names in your imports.

    Understanding changes to data source methods

    For each data source type, there is a factory method whose name ends in DataSource. These methods give you a builder object with methods for whatever options are appropriate. Pass that object to ConfigurationBuilder.DataSource.

    Here is an example:

    // 5.x model: setting custom options for streaming mode
    var config = Configuration.Builder("sdk-key-123abc")
    // 5.x model: specifying polling mode and setting custom polling options
    var config = Configuration.Builder("sdk-key-123abc")

    The default is to use streaming mode. Unlike the earlier model, you can no longer construct a meaningless configuration such as "use streaming mode, but set the polling interval to 1 minute" or "disable events, but set the flush interval to 10 seconds."

    Another data source option is the file-based data source. To learn more, read the API documentation for Launchdarkly.Sdk.Server.Integrations.FileData.

    Understanding changes to the data store

    The default data store is a simple in-memory cache. This is the same as earlier versions.

    If you want to use a persistent data store such as a database integration, you must call a DataStore factory method for that integration. This gives you a builder object with whatever options are appropriate for that database. Next, pass the object to Components.PersistentDataStore, a wrapper that provides caching options that are not specific to any one database but are built into the SDK. Put this into ConfigurationBuilder.DataStore.

    To learn more, read Persistent data stores.

    The following examples use the Redis integration:

    // 5.x model: use Redis, set custom Redis URI and key prefix, set cache TTL to 45 seconds
    var config = Configuration.Builder("sdk-key-123abc")
    .WithRedisUri(new Uri("redis://my-redis-host"))

    Understanding changes to events

    Analytics events are enabled by default. To customize their behavior, call Components.SendEvents() to get a builder object with event-related options, and then pass that object to ConfigurationBuilder.Events.

    To completely disable events, set ConfigurationBuilder.Events to Components.NoEvents.

    If you use private user attributes and are configuring private attributes for the entire SDK rather than for individual users, there is a new syntax based on the new UserAttribute type. This ensures that built-in attributes are not misspelled and helps to distinguish these parameters from other kinds of string parameters.

    Here is an example:

    // 5.x model: disabling events
    var config = Configuration.Builder("sdk-key-123abc")
    // 5.x model: customizing event behavior
    var config = Configuration.Builder("sdk-key-123abc")

    It is no longer possible to construct a meaningless configuration like "disable events, but set the flush interval to 10 seconds."

    Understanding changes to networking

    Options in this category affect how the SDK communicates with LaunchDarkly over HTTP/HTTPS, including connection timeout, proxy servers, and more. If you need to customize these, call Components.HttpConfiguration() to get a builder object, configure this builder, and then pass it to ConfigurationBuilder.Http.

    Some of the methods have changed slightly in terms of the type or number of parameters, and there is also a new method for specifying an HTTP proxy in your code rather than from an environment variable. More details are available in HttpConfigurationBuilder.

    Here is an example:

    // 5.x model: setting connection and read timeouts
    var config = Configuration.Builder("sdk-key-123abc")

    Understanding changes to EvaluationDetail and EvaluationReason

    The EvaluationDetail and EvaluationReason types, which were formerly in LaunchDarkly.Client, and are now in LaunchDarkly.Sdk, have been modified in the following ways:

    1. They are now structs rather than classes.
    2. EvaluationReason is no longer a base class with subclasses like EvaluationReason.Off for different reasons. Instead, it is always the same struct type, and you can distinguish one reason from another by looking at its properties such as Kind.
    3. EvaluationReason.RuleIndex is now an optional int? rather than an int. If it is not applicable (because the reason is not a rule match), the value of this property is now null. Previously, the special value of -1 was used to mean "not applicable."

    Understanding changes to add-on integration packages

    The Redis, Consul, and DynamoDB integrations have new major versions that are compatible with .NET SDK 6.0.

    The configuration syntax is available in Understanding changes to the data store.

    Understanding changes to logging

    Previously, the SDK used the Common.Logging framework, which provides adapters to various popular loggers. But writing the LaunchDarkly packages against such a third-party API causes inconvenience for any developer using LaunchDarkly who prefers a different framework. Also, Common.Logging is a relatively heavyweight solution for projects that may only have simple logging requirements.

    Starting in version 6.0, the SDK no longer has a built-in dependency on Common.Logging or on any other third-party logging framework. Instead it uses a new package, LaunchDarkly.Logging.

    The new package provides some basic built-in logging implementations suitable for simple applications, such as logging to the console.

    Here is an example of configuring the .NET SDK to send log output to the console, and to enable only log messages of Warn level or higher:

    using LaunchDarkly.Logging;
    using LaunchDarkly.Sdk.Server;
    var config = Configuration.Builder("sdk-key-123abc")

    It also has an adapter system for connecting it to other logging frameworks. If you use .NET Core, the built-in adapter that sends log output to the .NET Core logging framework is Microsoft.Extensions.Logging:

    var config = Configuration.Builder("sdk-key-123abc")

    Other adapters are defined in separate packages whose source code is in the dotnet-logging-adapters repository. For instance, if you add the package LaunchDarkly.Logging.Log4net, you can configure the SDK to send log output to log4net like this:

    var config = Configuration.Builder("sdk-key-123abc")

    The SDK's use of logger names has also changed. Most logging frameworks allow you to use logger names to configure different filtering rules for different kinds of messages, so if you have been using that feature you may need to adjust your configuration.

    Previously, most of the SDK's log output used the logger name LaunchDarkly.Client.LdClient, but some of it used the names of other classes such as Launchdarkly.Client.StreamProcessor. These class names were implementation details that were subject to change, so there was not a well-defined set of logger names.

    Starting in version 6.0, the SDK uses the following logger names:

    • Launchdarkly.Sdk: general messages that do not fall into any other categories
    • Launchdarkly.Sdk.DataSource: messages related to how the SDK obtains feature flag data-- normally this means messages about the streaming connection to LaunchDarkly, but if you use polling mode or file data instead, those will be logged under this name too
    • Launchdarkly.Sdk.DataStore: messages related to how feature flag data is stored-- for instance, database errors if you are using a database integration
    • Launchdarkly.Sdk.Evaluation: messages related to feature flag evaluation
    • Launchdarkly.Sdk.Events: messages related to analytics event processing

    The use of log levels has also changed. Previously, many kinds of I/O errors, such a network failure when the SDK was trying to make a streaming connection or sending events to LaunchDarkly, were logged at Error level. This could cause an unwanted amount of noise from monitoring systems, because such errors were often due to temporary problems that the SDK could recover from without intervention.

    Starting in version 6.0, if the SDK gets a network error that might interfere with receiving feature flag data from LaunchDarkly, it first logs it at the Warn level. It retries the connection as usual, and reports the problem again at the more serious Error level only if it remains unable to get a successful connection for a full minute. You can change that interval with LoggingConfigurationBuilder.

    Using the Relay Proxy

    There are two ways you can configure the SDK to use the Relay Proxy:

    • proxy mode, connecting to it via HTTP/HTTPS as if it were the LaunchDarkly service.
    • daemon mode, receiving flag data only through a database.

    The configuration syntax for both proxy mode and daemon mode has changed in the 6.x SDK.

    Here's how:

    // proxy mode
    var relayUri = new Uri("http://my-relay-host:8000");
    var config = Configuration.Builder("sdk-key-123abc")
    .EventsUri(relayUri) // if you want to proxy events
    // daemon mode with a Redis database
    var config = Configuration.Builder("sdk-key-123abc")
    RedisComponents.RedisFeatureStore().WithUri(new Uri("redis://my-redis-host"))

    Converting objects to or from JSON data

    You might want to convert LaunchDarkly SDK classes such as User, LdValue, or FeatureFlagsState into JSON if you are passing them to front-end JavaScript code. Less commonly, you might want to convert them from JSON. The SDK provides ways to do both.

    First, you can use the serialize and deserialize methods in LaunchDarkly.Sdk.Json.LdJsonSerialization to quickly convert things to or from JSON strings.

    Second, the System.Text.Json API (available on all platforms except .NET Framework 4.5.x) will correctly convert these types.

    Third, if you prefer to use the popular Newtonsoft Json.NET framework, read the following section.


    Previously, the SDK used Json.NET for all of its JSON operations, and defined custom encodings for types like FeatureFlagsState using that framework's JsonConverter API. That meant that if you wanted to convert one of those types to JSON with Json.NET, it worked automatically.

    However, there were problems with having a Json.NET dependency in the SDK. There are many versions of the Newtonsoft.Json package, so there could be version conflicts if an application was using both the LaunchDarkly .NET SDK and a different version of Json.NET. Another problem was that Json.NET has some nonstandard behaviors, such as automatically converting strings to dates, and could be customized globally in ways that could interfere with the SDK. Also, using the standard reflection-based serialization/deserialization mechanism in Json.NET is less efficient than other approaches.

    Starting in version 6.0, the SDK no longer uses Json.NET. Instead, it uses the System.Text.Json API, except on platforms where that API is not available (.NET Framework 4.5.x), in which case it uses a custom implementation. This removes the potential for package version conflicts, and also is significantly more efficient in terms of memory usage when the SDK is encoding or decoding JSON.

    However, this means that if you want to convert LaunchDarkly SDK types such as FeatureFlagsState to JSON, you can't simply call Newtonsoft.Json.JsonConvert.SerializeObject and get correct results, because Json.NET does not know about the custom serializers for these types in the SDK.

    If you want to make Json.NET work correctly with these types, you must add the package LaunchDarkly.CommonSdk.JsonNet, and then create Json.NET's JsonSerializerSettings as follows:

    var settings = new JsonSerializerSettings
    Converters = new List<JsonConverter>

    You can then use settings in any call to JsonConvert.SerializeObject or JsonConvert.DeserializeObject, or use it globally by modifying JsonConvert.DefaultSettings, and Json.NET will correctly handle the LaunchDarkly SDK types.

    Alternately, if you would rather not install this extra package, you can use LaunchDarkly.Sdk.Json.LdJsonSerialization and add an extra step to convert the JSON string to Json.NET's JRaw type:

    struct ValuesBeingPassedToJavaScriptCode
    public JRaw User;
    ValuesBeingPassedToJavaScriptCode CreateValuesForJavaScript(User user)
    var userJson = new JRaw(LdJsonSerialization.SerializeObject(user));
    return new ValuesBeingPassedToJavaScriptCode { User = userJson };

    Implementing custom components

    Most applications use either the default in-memory storage or one of the database integrations LaunchDarkly provides (Consul, DynamoDB, Redis), but the data store interface (formerly called "feature store") has always been public so developers can write their own integrations.

    Starting in .NET SDK 6.0, this model has been changed to make it easier to implement database integrations. The basic concepts are the same: the SDK defines its own "data kinds", such as feature flags and user segments. The data store must provide a way to add and update items of any of these kinds, without knowing anything about their properties except the key and version.

    The main changes are:

    • Caching is handled by the SDK, not by the store implementation. Now you only need to implement the lower-level operations of adding or updating data.
    • The SDK serializes and deserializes the data, so the store operates only on strings.
    • Data structures have been simplified to avoid the use of generics and maps.

    The interface for "data source" components that receive feature flag data, either from LaunchDarkly or from some other source, such as a file, has also changed slightly to use the new data store model.

    To learn more, read the API documentation for the IPersistentDataStore and IDataSource interfaces. You may also want to review the source code for one of the LaunchDarkly database integrations, such as Redis, to learn how it changed from the previous major version.

    Miscellaneous API changes

    Here are several changes to names and types that do not affect the basic functionality of the SDK, but were changed for consistency.

    • The Initialized() method of LdClient is now a read-only property, Initialized, instead of a method.
    • The IConfigurationBuilder interface has been replaced by the concrete class ConfigurationBuilder.
    • The ILdClient interface is now in LaunchDarkly.Sdk.Server.Interfaces instead of the main namespace.

    Understanding what was deprecated

    All types and methods that were marked as deprecated/obsolete in the last 5.x release have been removed from the 6.0 release. If you were using these with a recent version previously, you should already have received deprecation warnings at compile time, with suggestions about their recommended replacements.

    Understanding new functionality

    The 6.0 release also includes new features as described in the release notes.

    These include:

    • You can tell the SDK to notify you whenever a feature flag's configuration has changed with LdClient.FlagTracker. To learn more, read Subscribing to flag changes.
    • You can monitor the status of the SDK's connection to LaunchDarkly services with LdClient.DataSourceStatusProvider.
    • You can monitor the status of a persistent data store (for instance, to get caching statistics, or to be notified if the store's availability changes due to a database outage) with LdClient.DataStoreStatusProvider.
    • You can configure the SDK's use of different logging levels depending on the duration of a service outage with ConfigurationBuilder.Logging and LoggingConfigurationBuilder.

    To learn more, read the API documentation for these classes and methods.