Set KeepAlive to false when interacting with external hosts in a plug-in

Category: Performance

Impact potential: High

Symptoms

If a plug-in makes external web requests and is trying to use KeepAlive on a closed connection, the plug-in will ultimately fail to execute the web request. If the plug-in is registered:

• Synchronously, users may experience:

  • Unresponsive model-driven apps
  • Slow client interactions
  • The browser stops responding

• Asynchronously, plug-in executions may take an extended period of time before failing.

Guidance

1. In HTTP 1.1, all connections are considered persistent (KeepAlive is true) unless declared otherwise. Due to the fact that plug-ins run in isolation, the Sandbox service translates into them being short-lived executions that generally would not benefit from KeepAlive. To avoid problems with connecting to external services we recommend disabling KeepAlive within plug-ins. If your specific external service would benefit from using persistent sessions for performance reasons, actively send a KeepAlive at an interval of half the idle timeout (30 seconds) to keep the connection from closing.

The following examples show how to explicitly define KeepAlive to false based on the method you use to establish a connection to an external service:

• HttpWebRequest

  HttpWebRequest req = WebRequest.Create("https://www.contoso.com/api/stuff") as HttpWebRequest;
  
  if (req != null)
  {
      req.KeepAlive = false;
      HttpWebResponse response = (HttpWebResponse)req.GetResponse();
  }
  

• WebClient

  private string RequestString(Uri location)
  {
      using (var client = new MyWebClient())
      {
          return client.DownloadString(location);
      }
  }
  
  internal class MyWebClient : WebClient
  {
      // Overrides the GetWebRequest method and sets keep alive to false
      protected override WebRequest GetWebRequest(Uri address)
      {
          HttpWebRequest req = (HttpWebRequest)base.GetWebRequest(address);
          req.KeepAlive = false;
  
          return req;
      }
  }
  

• WCF ClientBase< T > Instance

  OrganizationServiceClient client = null;
  
  try
  {
      var address = new EndpointAddress("https://www.contoso.com/Custom.svc");
      var transport = new HttpsTransportBindingElement();
      transport.KeepAliveEnabled = false;
  
      var binding = new CustomBinding(transport);
  
      client = new OrganizationServiceClient(binding, address);
  
      WhoAmIResponse response = client.Execute(new WhoAmIRequest()) as WhoAmIResponse;
  }
  catch (Exception ex)
  {
      client.Abort();
  }
  finally
  {
      client.Close();
  }
  

• WCF ChannelFactory< TChannel > Static Method

  IRequestChannel channel = null;
  try
  {
      var address = new EndpointAddress("https://www.contoso.com/Custom.svc");
      var transport = new HttpsTransportBindingElement();
      transport.KeepAliveEnabled = false;
  
      var binding = new CustomBinding(transport);
  
      channel = ChannelFactory<IRequestChannel>.CreateChannel(binding, address);
  
      Message request = Message.CreateMessage(MessageVersion.Soap12, "some action", "message body");
      Message response = channel.Request(request);
  }
  catch (Exception ex)
  {
      channel.Abort();
  }
  finally
  {
      channel.Close();
  }
  

• WCF ChannelFactory< TChannel > Instance

  ChannelFactory<IRequestChannel> factory = null;
  IRequestChannel channel = null;
  try
  {
      var address = new EndpointAddress("https://www.contoso.com/Custom.svc");
      var transport = new HttpsTransportBindingElement();
      transport.KeepAliveEnabled = false;
  
      var binding = new CustomBinding(transport);
  
      factory = new ChannelFactory<IRequestChannel>(binding, address);
      channel = factory.CreateChannel();
  
      Message request = Message.CreateMessage(MessageVersion.Soap12, "some action", "message body");
      Message response = channel.Request(request);
  }
  catch (Exception ex)
  {
      channel.Abort();
      factory.Abort();
  }
  finally
  {
      channel.Close();
      factory.Close();
  }
  

Problematic patterns

In order to override the default value of KeepAlive for the non-WCF interactions, the approach should be taken to leverage HttpWebRequest to perform the interactions with the web server, but first setting the KeepAlive property to false.

The following examples show the problematic pattern based on the method you use to establish a connection to an external service:

Warning

These patterns should be avoided.

• HttpWebRequest

  WebRequest request = WebRequest.Create("https://www.contoso.com/api/stuff");
  //KeepAlive not explicitly defined as true.  However, default behavior is KeepAlive = true.
  HttpWebResponse response = (HttpWebResponse)request.GetResponse();
  response.Close();
  

• WebClient

  using (var client = new WebClient())
  {
      string url = "https://www.contoso.com/api/stuff";
      //KeepAlive not explicitly defined as true.  However, default behavior is KeepAlive = true.
      string result = client.DownloadString(url);
  }
  

• WCF ClientBase< T > Instance

  OrganizationServiceClient client = null;
  
  try
  {
      var address = new EndpointAddress("https://www.contoso.com/Custom.svc");
      var binding = new BasicHttpsBinding();
      //KeepAlive not explicitly defined as true.  However, default behavior is KeepAlive = true.
      client = new OrganizationServiceClient(binding, address);
  
      WhoAmIResponse response = client.Execute(new WhoAmIRequest()) as WhoAmIResponse;
  }
  catch (Exception ex)
  {
      client.Abort();
  }
  finally
  {
      client.Close();
  }
  

• WCF ChannelFactory< TChannel > Static Method

  IRequestChannel channel = null;
  try
  {
      var address = new EndpointAddress("https://www.contoso.com/Custom.svc");
      var binding = new BasicHttpsBinding();
      //KeepAlive not explicitly defined as true.  However, default behavior is KeepAlive = true.
  
      channel = ChannelFactory<IRequestChannel>.CreateChannel(binding, address);
  
      Message request = Message.CreateMessage(MessageVersion.Soap12, "some action", "message body");
      Message response = channel.Request(request);
  }
  catch (Exception ex)
  {
      channel.Abort();
  }
  finally
  {
      channel.Close();
  }
  

• WCF ChannelFactory< TChannel > Instance

  ChannelFactory<IRequestChannel> factory = null;
  IRequestChannel channel = null;
  try
  {
      var address = new EndpointAddress("https://www.contoso.com/Custom.svc");
      var binding = new BasicHttpsBinding();
      //KeepAlive not explicitly defined as true.  However, default behavior is KeepAlive = true.
  
      factory = new ChannelFactory<IRequestChannel>(binding, address);
      channel = factory.CreateChannel();
  
      Message request = Message.CreateMessage(MessageVersion.Soap12, "some action", "message body");
      Message response = channel.Request(request);
  }
  catch (Exception ex)
  {
      channel.Abort();
      factory.Abort();
  }
  finally
  {
      channel.Close();
      factory.Close();
  }
  

Additional information

Plug-ins interacting with external services may experience abnormally increased execution times. The problem is due to the (KeepAlive property) of HTTP requests issued to external web servers. If the KeepAlive property is set to true or not defined at all (default behavior is true) the Sandbox client on the server could continue to try and use a persistent session even though the session has become expired due to network device configuration. The cause of the extended execution time is due to the network retrying the request until the connection is, ultimately, reset.

Important

This affects all code that initiates HTTP Requests to a web server using System.Net.WebClient, System.Net.WebRequest or System.Net.HttpWebRequest as well as Windows Communications Foundation (WCF) client communications using an HTTP transport binding directly or indirectly via ChannelFactory<TChannel> or ClientBase<T>.

This behavior is transparent to end users and traditional logging as the execution is due to network delays. If the plug-in was registered as a synchronous event, users could experience intermittent performance issues during those registered operations which could cause unresponsiveness of model-driven apps. If the plug-in is registered asynchronously, the issue would only be observed by reviewing execution times of the plug-in and seeing the execution taking longer than normal or expected.

See also

Sample: Web access from a sandboxed plug-in
Load Balancing (WCF)
HttpTransportBindingElement.KeepAliveEnabled Property
HttpWebRequest.KeepAlive Property