Does Azure Cloud Service Load Balancer take Role Status into account?

0
votes

Here's my scenario:

I have an Azure Cloud Service that runs a "hefty" .NET WCF project. The heftiness comes in with the startup tasks, as we cache a large amount of data into memory to make the project run quickly.

We're have some logic to override the OnStart method of the RoleInstance to perform this caching, so the instance doesn't return as "Ready" until all of this caching is completed.

When we deploy our service, we have 2 instances (so theyre on separate Fault\Update domains).

To that scenario I have 2 questions:

  1. When we deploy an update or Microsoft performs maintenance against one of these managed VM's, does the Azure Load Balancer take the role state into account and not route traffic to it until it's in a "Ready" state?

  2. For the aforementioned Load Balancer, do I have to configure anything for the cloud service to balance between the multiple instances? I was always under the impression that Microsoft managed that for you.. this way if you scale out to N role instances, the cloud service will take into account the number if instances and assign load accordingly.

Thanks!

1
azure

1 Answers

1
votes

It is handled for you. The load balancer probe communicates with the guest agent on each VM which only returns an HTTP 200 once the role is in the Ready state. However, if you’re using a web role and running w3wp.exe on it, the load balancer is not able to detect any failures like HTTP 500 responses that it may generate.

In that case, you’d need to insert an appropriate LoadBalancerProbe section in your .csdef file and also properly handle the OnStop event. This article describes the default load balancer behaviour in more detail, as well as how to customise it.