Adapt WCF automatically to current resources?

Question

Is it possible to adapt a WCF service to the current resources, for example change the concurrent calls to a lower nr if the ram is low?

BestRegards

Answer 1

In fact, it's already the case since .net 4 (see blog post here). However, only the number of processor is important.

• MaxConcurrentSessions: default is 100 * ProcessorCount
• MaxConcurrentCalls: default is 16 * ProcessorCount
• MaxConcurrentInstances: default is the total of the above two, which follows the same pattern as before.

HTTP is a stateless protocol and it's recommanded to avoid using session on server side, for scalability. A typical front end server, consumme CPU and not memory (ScaleOut Vs ScaleUp).

However, WCF limits, aka WCF throttling is just a behavior. You add/edit this behavior at startup using a ServiceHost a custom ServiceHostFactory.

ServiceThrottlingBehavior throttle = new ServiceThrottlingBehavior();
throttle.MaxConcurrentCalls = /*what you want*/;
throttle.MaxConcurrentSessions = /*what you want*/;
throttle.MaxConcurrentInstances = /*what you want*/; 

ServiceHost host = new ServiceHost(typeof(TestService));    
// if host has behaviors, remove them.
if (host.Description.Behaviors.Count != 0)
{
   host.Description.Behaviors.Clear();
}
// add dynamically created throttle behavior
host.Description.Behaviors.Add(throttle);

//open host
host.Open();

You can achieve the same using a custom ServiceHostFactory.

<%@ ServiceHost Language="C#" Debug="true" Service="MyWebApplication.TestService"
                Factory="MyWebApplication.TestServiceHostFactory" %>