Why should i use a LoadBalancerProbe instead of subscribing to the RoleEnvironment.StatusCheck Event? - azure

Question

I was fiddling with the options azure provides to balance the load between multiple webroles.
I found three possible ways to do this.
the first would be to do nothing at all and let the default ( round robin) implementation do the job.
the second possibility would be to define a custom LoadBalancerProbe in the ServiceDefinitionFile, which i tried and did not get to work: From my understanding the custom aspx page is called each time a status check is performed on the role. Depending on the http response code the role changes its status to busy. - but this is never happening.
Also, i couldnt really find any examples for defining a custom LoadBalancingProbe.
Thus i looked for an alternative way to do this.
Now iam subscribing to the RoleEnvironment.StatusCheck Event, which allows me to implement some logic and depending on the results set the role state to busy and available.
My Questions:
1) Supposing the Custom LoadBalancerProbe works as described in the MSDN, what is the difference between subscribing to the StatusCheckEvent and using a custom probe?
2) Why does my custom load balancer probe not work ? - iam just testing with the azure emulator for now and iam well aware that traffic still gets routed to the webrole instances allthough they are set to busy in the emulator.
But my Custom Probe does not change the status of the webroleinstances at all.
Here is the very rudimentary code, which should - to my knowledge set the status of webrole instance_n_0 to busy.
public class LoadBalanceController : Controller
{
public ActionResult Index()
{
WebOperationContext woc = WebOperationContext.Current;
if(RoleEnvironment.CurrentRoleInstance.Id.ToLower().Contains("_0"))
{
woc.OutgoingResponse.StatusCode = System.Net.HttpStatusCode.ServiceUnavailable;
}else
{
woc.OutgoingResponse.StatusCode = System.Net.HttpStatusCode.OK;
}
return View(); //not relevant
}
Ive also configered my servicedefinitionfile and set a Route to redirect to this controller/action when calling the healthcheck.aspx defined in the custom probe.
<LoadBalancerProbes>
<LoadBalancerProbe name="WebRoleBalancerProbeHttp" protocol="http" path="healthcheck.aspx" intervalInSeconds="5" timeoutInSeconds="100"/>
</LoadBalancerProbes>
...
<InputEndpoint name="EndpointWeb" protocol="http" port="80" loadBalancerProbe="WebRoleBalancerProbeHttp"/>
The Route:
routes.MapRoute(
name: "HealhCheck",
url: "healthcheck.aspx",
defaults: new { controller = "LoadBalance", action = "Index", id = UrlParameter.Optional }
);

Answer 1

Not sure why the custom probe isn't working, but for the differences: The health-check event lets you announce whether an instance is available, but you don't have any flexibility in terms of how often this is called. Also, you can't launch a separate service that listens on a custom port (or port type).
You have much more flexibility with custom probes, since you can create any type of port listener to determine health, even a separate exe.
With Virtual Machines, this is the only method of health probes, since Virtual Machines don't have the guest agent running and don't provide the health-check event.

Answer 2

In your service definition file, you have marked your probe to be hosted on an http endpoint (and not HTTPS).
Is that the case with your web app as well ? Is it exposing that endpoint on HTTP and not on HTTPS ? If yes, then also check if there is any automatic redirection to HTTPS happening.
I think you have mostly setup everything properly. Here is a post that has some example code and another question from SO, where they were successful in setting it up (should provide some insight into the csdef file).
I agree with David Makogon's points about the differences between the two.