Session handling in audience criteria

4 min

You can use the built-in Optimizely audience criteria without requiring session state on the server side by manually turning off ASP.NET session states. The audience system can autodetect if the session state was turned off and switches to a cookie-based approach for audience criteria that previously used sessions. You can also customize your storage of users' audience sessions.

RaiseStartSession

If the session is turned on, then the AspNet session start event raises the RaiseStartSession event. If the session is disabled, then the RaiseStartSession event is raised by HttpApplication AcquireRequestState event.

Session State

The session-based audience criterion saves its session state inside a session, cookie, or customized state storage. If the session is enabled and there is no registered custom storage, then it uses an HTTP session object as storage. If the session is disabled and there is no registered custom storage, then it uses an HTTP cookie as storage.

Turn on and off session state

The HTTP session object defaults if the AspNet session state mode is not Off. It can be changed explicitly by setting false the property EnableSession on the VisitorGroupOptions options.

Customize state storage

To customize storage, it is needed to implement the IStateStorage interface and register it.

This sample code shows customized state storage and turns the session state off.

internal class InMemoryStateStorage: IStateStorage {
  IDictionary<string, string> _states = new Dictionary<string, string>();
  public bool IsAvailable => true;
  public object Load(string key) {
    _states.TryGetValue(key, out string value);
    return value;
  }

  public void Save(string key, object value) {
    _states[key] = (string) value;
  }

  public void Delete(string key) {
    _states.Remove(key);
  }
}

and the custom state storage can be registered in IServiceCollection in the startup, like this:

public class Startup {
  public void ConfigureServices(IServiceCollection services) {
    services.Add<VisitorGroupOptions>((s) => new VisitorGroupOptions(), ServiceInstanceScope.Singleton);
    services.Configure<VisitorGroupOptions> (s => s.EnableSession = EnableSession);
    services.Add<IStateStorage>(s => new InMemoryStateStorage(), ServiceInstanceScope.Singleton);
  }
}