Azure Web Role Shutdown (When and How?)

Question

When the Azure platform decides to shut down one of my web role instances, how is that accomplished?

For example, does it stop sending new requests, but allows the existing requests to complete? I cannot imagine that it just terminates active connections for routine maintenance. That would be highly disruptive and costly.

Any insight into this little black box would be great, especially if you know of an MSDN or Azure CAT link that goes into this.

Answer 1

The Fabric Controller will remove the instance from the load balancer so it receives no new requests. It will then proceed to a clean shutdown sequence, first shutting down ASP.NET through its regular life cycle (will may vary depending on whether your application is running under integrated or classic mode), waiting for the requests to end (for up to the duration specified in the shutdownTimeLimit property), then raising the RoleEnvironment.Stopping event and calling the role's OnStop method for cleanup. At last, the Job Object will be terminated.

References:

• Real World: Startup Lifecycle of a Windows Azure Role
• Overview of Building an Application that Runs in a Hosted Service
• RoleEnvironment.Stopping Event
• ASP.NET Application Life Cycle Overview for IIS 5.0 and 6.0
• ASP.NET Application Life Cycle Overview for IIS 7.0
• RoleEntryPoint.OnStop Method
• TerminateJobObject function
• Health Application Pool Settings
• Process Model Settings for an Application Pool