Feature Flags — The Deployment Superpower You Are Probably Not Using

public IActionResult GetDashboard()
{
    if (_flags.IsEnabled("new_dashboard", userId))
        return View("NewDashboard");

    return View("OldDashboard");
}

var context = new EvaluationContext
{
    UserId  = "user_9821",
    Plan    = "enterprise",
    Region  = "South India",
    City    = "Bengaluru",
    Country = "IN",
    Company = "Infoveave",
    Role    = "admin",
    Custom  = new Dictionary<string, string>
    {
        { "accountAge", "18months" }
    }
};

bool showFeature = _flags.IsEnabled("new_report_builder", context);

userId IS IN ["user_001", "user_002"]

region IS IN ["Karnataka", "Maharashtra"]

plan IS IN ["pro", "enterprise"]

company IS IN ["Infoveave", "TataConsultancy"]

plan IS "enterprise"
  AND region IS "South India"
  AND role IS "admin"
→ Only enterprise admins from South India see this feature

public bool IsInRollout(string userId, string flagKey, int percentage)
{
    string input = $"{userId}:{flagKey}";
    using var md5 = MD5.Create();
    byte[] hash  = md5.ComputeHash(Encoding.UTF8.GetBytes(input));
    int bucket   = Math.Abs(BitConverter.ToInt32(hash, 0)) % 100;
    return bucket < percentage;
}

// .NET — evaluate on the server, send decisions to frontend
var features = new {
    newReportBuilder = _flags.IsEnabled("new_report_builder", userId),
    advancedExport   = _flags.IsEnabled("advanced_export", userId)
};

// React — consume via context hook
const ReportPage = () => {
    const hasNewBuilder = useFeature("newReportBuilder");
    return hasNewBuilder ? <NewReportBuilder /> : <OldReportBuilder />;
};

// API — gate the endpoint too, not just the UI
[HttpPost("report/advanced")]
public IActionResult GenerateAdvancedReport()
{
    if (!_flags.IsEnabled("advanced_export", GetUserId()))
        return Forbid();
}

// Avoid — called twice
_flags.IsEnabled("new_dashboard", userId);
_flags.IsEnabled("new_dashboard", userId);

var featureCache = new Dictionary<string, bool>();

bool IsEnabledCached(string key, string userId)
{
    if (!featureCache.ContainsKey(key))
        featureCache[key] = _flags.IsEnabled(key, userId);

    return featureCache[key];
}

// Avoid — three round trips
var a = _flags.IsEnabled("A", userId);
var b = _flags.IsEnabled("B", userId);
var c = _flags.IsEnabled("C", userId);

// Prefer — one round trip
var features = _flags.GetAll(userId);
features["A"];
features["B"];
features["C"];