How to Stop single Instance/VM of WebRole/WorkerRole

Question

We have a VM say SampleVM depoyed & running on Azure Environment and on the same we have created 2 instances One is WebRole & other is WorkerRole running onto Slot staging.

My prob is I am able to Start/Stop SampleVM through powershell command but How can I Start/Stop a single instance(WebRole or WorkerRole) running on a SampleVM.

However when I stop SampleVM then both the Instance also stopped but I want to stop only one Instance/VM i.e. WebRole Or WorkerRole.

Please provide some powershell command with the argument pass to Stop/Start a single instance

Answer 1

Good answer by Gaurav, but I wanted to add a bit more detail, as I think there may be a bit of confusion around web and worker roles. Each role is a definition for a group of virtual machines that do the same thing, as constructed by you (you don't deal with the OS - you just kickstart your app, and Azure takes care of the VM itself).

When a Cloud Service is running, there will be a minimum of one instance of each role type. So in your case, running both a web role and worker role, you'll have at least two VMs running.

If you choose to scale out your web role to, say, 3 instances, and then decide to dial it back to 2 instances, you cannot choose which one to shut down; this is taken care of by Azure's fabric. Remember that each instance of a role is running identical code, and Azure load-balances traffic to your role instances (through external endpoints that you define). The only thing you need to worry about is shutdown. You have approx. 5 minutes to clean up any running processes (and you can easily take a particular instance out of the load balancer during shutdown, since you receive a Stopping() event).

You cannot shut down an entire role (e.g. all instances of a role) within a cloud service (so... you can't take down your worker role instances while leaving your web role instances running). If that's a requirement, then you can always consider running your web role in one Cloud Service and worker role in another Cloud Service. If they use queues to pass data, everything will still work as before. If the web role instances need direct access to worker role instances, you could put both Cloud Services into a Virtual Network.

One more thing to consider: You don't have to have separate roles. If cost is a factor, you can run all your code in your web role. Takes little work to spin up additional processes / threads in your web role, during OnStart() - remember that role instances are full Windows Server virtual machines; run whatever you want. With a single role definition, scaling is a bit coarse: Everything is scaled together. With separate roles, you can fine-tune your scaling (much more important when building larger systems).

Answer 2

David's broader points about how to model your PaaS service are all correct. But to add to it, there is a new Service Management API that has just been released called Delete Role Instance which will let you delete a specific instance of a role - http://msdn.microsoft.com/en-us/library/windowsazure/dn469418.aspx. This functionality is brand new to allow you to choose which instance to delete instead of being subject to the default fabric behavior that David describes (always deleting the last instance).

Answer 3

Simple answer is that as of today, you can't stop a single instance of your web/worker role. When you stop a role, all instances are stopped. You could remove instances from your role but again you can't specify which particular instance you want to remove. See @kwill's answer below.

You may also find following links useful for deleting specific role instances:

http://gauravmantri.com/2013/10/16/a-new-version-of-windows-azure-service-management-api-is-available-with-delete-specific-role-instances-and-more-goodies/

https://github.com/richorama/Two10.Azure.SelfDestruct