Feature flags - ConfigCat

ConfigCat is a feature flag service that allows to toggle features on or off after deploying code. It offers support for percentage rollouts, A/B testing, and feature variations. By integrating ConfigCat with the LeanCode CoreLibrary, you can effortlessly harness its feature-flag capabilities. For in-depth information about ConfigCat, explore the official documentation and the .NET SDK documentation.

Packages

Package	Link	Application in section
ConfigCat.Client		Client
LeanCode.ConfigCat		Configuration

Configuration

To incorporate ConfigCat into your LeanCode CoreLibrary-based application, follow the example below. This example showcases the usage of the AddConfigCat(...) method to register the ConfigCatClient:

public override void ConfigureServices(IServiceCollection services)
{
    // . . .

    services.AddConfigCat(
        sdkKey: null,
        flagOverridesFilePath: "YOUR_PATH/configcat.json",
        overrideBehaviour: OverrideBehaviour.LocalOnly);

    // . . .
}

Then you can define configcat.json file:

{
    "flags": {
        "SendEmployeeAssignedToAssignmentEmails": false,
    }
}

In the example above, ConfigCat is configured to retrieve feature flags directly from a configcat.json file specified in the flagOverridesFilePath argument, bypassing the ConfigCat CDN by using the OverrideBehaviour.LocalOnly setting. If you want to fetch values from the ConfigCat CDN, you must set the sdkKey and modify the overrideBehaviour argument with one of the following options:

public enum OverrideBehaviour
{
    //
    // Summary:
    //     When evaluating values, the SDK will not use feature
    //     flags and settings from the ConfigCat CDN, but it will
    //     use all feature flags and settings that are loaded from
    //     local-override sources.
    LocalOnly,
    //
    // Summary:
    //     When evaluating values, the SDK will use all feature
    //     flags and settings that are downloaded from the ConfigCat CDN,
    //     plus all feature flags and settings that are loaded from
    //     local-override sources. If a feature flag or a setting
    //     is defined both in the fetched and the local-override
    //     source then the local-override version will take precedence.
    LocalOverRemote,
    //
    // Summary:
    //     When evaluating values, the SDK will use all feature flags
    //     and settings that are downloaded from the ConfigCat CDN, plus
    //     all feature flags and settings that are loaded from local-override
    //     sources. If a feature flag or a setting is defined both in the
    //     fetched and the local-override source then the fetched version
    //     will take precedence.
    RemoteOverLocal
}

You can also explore the various IServiceCollection ConfigCat extensions to register ConfigCat according to your preferences.

Feature flags usage

After configuration, you can use feature flag defined above to modify behaviour of an application to not send EmployeeAssignedToAssignmentEmail email when employee has been assigned to assignment:

public class SendEmailToEmployeeOnEmployeeAssignedToAssignment
    : IConsumer<EmployeeAssignedToAssignment>
{
    private readonly IEmailSender emailSender;
    private readonly IRepository<Employee, EmployeeId> employees;
    private readonly IRepository<Assignment, AssignmentId> assignments;
    private readonly IConfigCatClient configCat;

    public SendEmailToEmployeeOnEmployeeAssignedToAssignment(
        IEmailSender emailSender,
        IRepository<Employee, EmployeeId> employees,
        IRepository<Assignment, AssignmentId> assignments,
        IConfigCatClient configCat)
    {
        this.emailSender = emailSender;
        this.employees = employees;
        this.assignments = assignments;
        this.configCat = configCat;
    }

    public async Task Consume(
        ConsumeContext<EmployeeAssignedToAssignment> context)
    {
        if (await configCat.GetValueAsync(
                key: "SendEmployeeAssignedToAssignmentEmails",
                defaultValue: false,
                cancellationToken: context.CancellationToken))
        {
            var msg = context.Message;

            var employee = await employees.FindAndEnsureExistsAsync(
                msg.EmployeeId,
                context.CancellationToken);

            var assignment = await assignments.FindAndEnsureExistsAsync(
                msg.AssignmentId,
                context.CancellationToken);

            await emailSender.SendEmployeeAssignedToAssignmentEmailAsync(
                employee,
                assignment,
                context.CancellationToken);
        }
    }
}